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C++ Programming Code Examples

C++ > Visual C++ 5.0 Standard C++ Library Code Examples

Returns a const iterator which points just beyond the last object in the container.

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Returns a const iterator which points just beyond the last object in the container. end Header <deque> const_iterator end()const Returns a const iterator which points just beyond the last object in the container. If the container is empty, the result is undefined. iterator end() Returns an iterator which points just beyond the last object in the container. If the container is empty, the result is undefined. Sample #include <deque> #include <iostream> int main() { //default constructor std::deque<int> c1 ; //create deque with 10 copies of 4 std::deque<int> c2(10, 4) ; //copy constructor std::deque<int> c3(c2) ; int ai[] = {0, 1, 2, 3, 4, 5} ; int i ; std::deque<int> c4 ; //get_allocator std::deque<int>::allocator_type a1 = c4.get_allocator() ; //push_back for(i = 0; i < 5; i++) c4.push_back(ai[i]) ; //range copy constructor std::deque<int> c5(c4.begin(), c4.end()) ; //begin, end std::cout << "c4 (using begin, end) = " ; std::deque<int>::iterator Iter ; for(Iter = c4.begin(); Iter != c4.end(); Iter++) std::cout << *Iter << ", " ; std::cout << std::endl ; //rbegin, rend std::cout << "c4 (using rbegin, rend) = " ; std::deque<int>::reverse_iterator RevIter ; for(RevIter = c4.rbegin(); RevIter != c4.rend(); RevIter++) std::cout << *RevIter << ", " ; std::cout << std::endl ; //assign c2.assign(c5.begin(), c5.begin() + 3) ; c1.assign(10, 4) ; //at std::cout << "third element in c1 = " << c1.at(3) << std::endl ; //operator[] std::cout << "c4[3] = " << c4[3] << std::endl ; //back std::cout << "last element in c2 = " << c2.back() << std::endl ; //front std::cout << "first element in c2 = " << c2.front() << std::endl ; //size std::cout << "number of elements in c2 = " << c2.size() << std::endl ; //max_size std::cout << "max number of elements c2 can hold using current allocator = " << c2.max_size() << std::endl ; //erase c3.erase(c3.begin(), c3.begin() + 4) ; //clear c2.clear() ; //empty if (c2.empty() == true) std::cout << "c2 is now empty" << std::endl ; //resize c2.resize(10, 30) ; std::cout << "number of elements in c2 = " << c2.size() << std::endl ; std::cout << "last element in c2 = " << c2.back() << std::endl ; std::cout << "first element in c2 = " << c2.front() << std::endl ; //push_front c2.push_front(25) ; std::cout << "first element in c2 = " << c2.front() << std::endl ; //pop_back c2.pop_back() ; std::cout << "last element in c2 = " << c2.back() << std::endl ; //pop_front c2.pop_front() ; std::cout << "first element in c2 = " << c2.front() << std::endl ; //swap c3.swap(c2) ; std::cout << "number of elements in c3 = " << c3.size() << std::endl ; std::cout << "last element in c3 = " << c3.back() << std::endl ; std::cout << "first element in c3 = " << c3.front() << std::endl ; //insert c1.insert(c1.begin(), 20) ; c1.insert(c1.begin()+1, 4, 10) ; c1.insert(c1.begin()+2, c5.begin(), c5.end()) ; std::cout << "c1 = " ; for(Iter = c1.begin(); Iter != c1.end(); Iter++) std::cout << *Iter << ", " ; std::cout << std::endl ; return 0 ; } Program Output c4 (using begin, end) = 0, 1, 2, 3, 4, c4 (using rbegin, rend) = 4, 3, 2, 1, 0, third element in c1 = 4 c4[3] = 3 last element in c2 = 2 first element in c2 = 0 number of elements in c2 = 3 max number of elements c2 can hold using current allocator = 1073741823 c2 is now empty number of elements in c2 = 10 last element in c2 = 30 first element in c2 = 30 first element in c2 = 25 last element in c2 = 30 first element in c2 = 30 number of elements in c3 = 9 last element in c3 = 30 first element in c3 = 30 c1 = 20, 10, 0, 1, 2, 3, 4, 10, 10, 10, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
Deque Library operator[] Index in C++
Access element. Returns a reference to the element at position n in the deque container. This operator is used to reference the element present at position given inside the operator. It is similar to the at() function, the only difference is that the at() function throws an out-of-range exception when the position is not in the bounds of the size of deque, while this operator causes undefined behavior. A similar member function, deque::at, has the same behavior as this operator function, except that deque::at is bound-checked and signals if the requested position is out of range by throwing an out_of_range exception.
Syntax for Deque operator[] Index in C++
#include <deque> reference operator[] (size_type n); const_reference operator[] (size_type n) const;
n
Position of an element in the container. Notice that the first element has a position of 0 (not 1). Member type size_type is an unsigned integral type. Function returns the element at the specified position in the container. Member types reference and const_reference are the reference types to the elements of the container (see deque member types).
Complexity
Constant
Iterator validity
No changes
Data races
The container is accessed (neither the const nor the non-const versions modify the container). Element n is potentially accessed or modified. Concurrently accessing or modifying other elements is safe.
Exception safety
If the container size is greater than n, the function never throws exceptions (no-throw guarantee). Otherwise, the behavior is undefined (which may include throwing).
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/* C++ Deque operator[] function is used to access the element at specified position pos. If position pos is greater than the size of container then it returns a value 0. */ /* Access element from Deque by operator[] code example */ // deque::operator[] example: reversing order #include <iostream> #include <deque> int main () { std::deque<int> mydeque (10); // 10 zero-initialized elements std::deque<int>::size_type sz = mydeque.size(); // assign some values: for (unsigned i=0; i<sz; i++) mydeque[i]=i; // reverse order of elements using operator[]: for (unsigned i=0; i<sz/2; i++) { int temp; temp = mydeque[sz-1-i]; mydeque[sz-1-i]=mydeque[i]; mydeque[i]=temp; } // print content: std::cout << "mydeque contains:"; for (unsigned i=0; i<sz; i++) std::cout << ' ' << mydeque[i]; std::cout << '\n'; return 0; }
Deque Library empty() Function in C++
Test whether container is empty. Returns whether the deque container is empty (i.e. whether its size is 0). empty() function is used to check if the deque container is empty or not. This is an inbuilt function from C++ Standard Template Library(STL). This function belongs to the <deque> header file. The function either returns true or false, depending on whether the deque is empty or not. This function does not modify the container in any way. To clear the content of a deque container, see deque::clear.
Syntax for Deque empty() Function in C++
#include <deque> bool empty() const noexcept;
Function takes no parameter. Function returns true if the container size is 0, false otherwise.
Complexity
Constant
Iterator validity
No changes
Data races
The container is accessed. No contained elements are accessed: concurrently accessing or modifying them is safe.
Exception safety
No-throw guarantee: this member function never throws exceptions.
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/* deque::empty() is an inbuilt function in C++ STL which is declared in <deque> header file. deque::empty() checks whether the given deque container is empty(size is 0) or not, and returns true value if the container associated with the function is empty and false if the container is not empty. */ /* Test whether container is empty by deque::empty() function code example */ #include <deque> #include <iostream> using namespace std; int main(){ int product = 1; deque<int> Deque; //inserting elements to a deque using push_back() function Deque.push_back(10); Deque.push_back(20); Deque.push_back(30); Deque.push_back(40); Deque.push_back(50); //traversing deque while it willn't gets empty using empty() function while(!Deque.empty()){ product = product * Deque.front(); Deque.pop_front(); } //check if deque is empty or not if(Deque.empty()){ cout<<"Deque is empty and hence product is : "<<product; } else { cout<<"Deque is not empty "; } return 0; }
For Loop Statement in C++
In computer programming, loops are used to repeat a block of code. For example, when you are displaying number from 1 to 100 you may want set the value of a variable to 1 and display it 100 times, increasing its value by 1 on each loop iteration. When you know exactly how many times you want to loop through a block of code, use the for loop instead of a while loop. A for loop is a repetition control structure that allows you to efficiently write a loop that needs to execute a specific number of times.
Syntax of For Loop Statement in C++
for (initialization; condition; update) { // body of-loop }
initialization
initializes variables and is executed only once.
condition
if true, the body of for loop is executed, if false, the for loop is terminated.
update
updates the value of initialized variables and again checks the condition. A new range-based for loop was introduced to work with collections such as arrays and vectors.
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/* For Loop Statement in C++ Language */ // C++ program to find the sum of first n natural numbers // positive integers such as 1,2,3,...n are known as natural numbers #include <iostream> using namespace std; int main() { int num, sum; sum = 0; cout << "Enter a positive integer: "; cin >> num; for (int i = 1; i <= num; ++i) { sum += i; } cout << "Sum = " << sum << endl; return 0; }
Iterators in C++ Language
Iterators are just like pointers used to access the container elements. Iterators are one of the four pillars of the Standard Template Library or STL in C++. An iterator is used to point to the memory address of the STL container classes. For better understanding, you can relate them with a pointer, to some extent. Iterators act as a bridge that connects algorithms to STL containers and allows the modifications of the data present inside the container. They allow you to iterate over the container, access and assign the values, and run different operators over them, to get the desired result.
Syntax for Iterators in C++
<ContainerType> :: iterator; <ContainerType> :: const_iterator;
• Iterators are used to traverse from one element to another element, a process is known as iterating through the container. • The main advantage of an iterator is to provide a common interface for all the containers type. • Iterators make the algorithm independent of the type of the container used. • Iterators provide a generic approach to navigate through the elements of a container. Operator (*) : The '*' operator returns the element of the current position pointed by the iterator. Operator (++) : The '++' operator increments the iterator by one. Therefore, an iterator points to the next element of the container. Operator (==) and Operator (!=) : Both these operators determine whether the two iterators point to the same position or not. Operator (=) : The '=' operator assigns the iterator. Iterators can be smart pointers which allow to iterate over the complex data structures. A Container provides its iterator type. Therefore, we can say that the iterators have the common interface with different container type. The container classes provide two basic member functions that allow to iterate or move through the elements of a container: begin(): The begin() function returns an iterator pointing to the first element of the container. end(): The end() function returns an iterator pointing to the past-the-last element of the container. Input Iterator: An input iterator is an iterator used to access the elements from the container, but it does not modify the value of a container. Operators used for an input iterator are: Increment operator(++), Equal operator(==), Not equal operator(!=), Dereference operator(*). Output Iterator: An output iterator is an iterator used to modify the value of a container, but it does not read the value from a container. Therefore, we can say that an output iterator is a write-only iterator. Operators used for an output iterator are: Increment operator(++), Assignment operator(=). Forward Iterator: A forward iterator is an iterator used to read and write to a container. It is a multi-pass iterator. Operators used for a Forward iterator are: Increment operator(++), Assignment operator(=), Equal operator(=), Not equal operator(!=). Bidirectional iterator: A bidirectional iterator is an iterator supports all the features of a forward iterator plus it adds one more feature, i.e., decrement operator(--). We can move backward by decrementing an iterator. Operators used for a Bidirectional iterator are: Increment operator(++), Assignment operator(=), Equal operator(=), Not equal operator(!=), Decrement operator(--). Random Access Iterator: A Random Access iterator is an iterator provides random access of an element at an arbitrary location. It has all the features of a bidirectional iterator plus it adds one more feature, i.e., pointer addition and pointer subtraction to provide random access to an element. Following are the disadvantages of an iterator: • If we want to move from one data structure to another at the same time, iterators won't work. • If we want to update the structure which is being iterated, an iterator won?t allow us to do because of the way it stores the position. • If we want to backtrack while processing through a list, the iterator will not work in this case. Following are the advantages of an iterator: • Ease in programming: It is convenient to use iterators rather than using a subscript operator[] to access the elements of a container. If we use subscript operator[] to access the elements, then we need to keep the track of the number of elements added at the runtime, but this would not happen in the case of an iterator. • Code Reusability: A code can be reused if we use iterators. In the above example, if we replace vector with the list, and then the subscript operator[] would not work to access the elements as the list does not support the random access. However, we use iterators to access the elements, then we can also access the list elements. • Dynamic Processing: C++ iterators provide the facility to add or delete the data dynamically.
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/* Iterators in C++ language */ // C++ code to demonstrate the working of next() and prev() #include<iostream> #include<iterator> // for iterators #include<vector> // for vectors using namespace std; int main() { vector<int> ar = { 1, 2, 3, 4, 5 }; // Declaring iterators to a vector vector<int>::iterator ptr = ar.begin(); vector<int>::iterator ftr = ar.end(); // Using next() to return new iterator // points to 4 auto it = next(ptr, 3); // Using prev() to return new iterator // points to 3 auto it1 = prev(ftr, 3); // Displaying iterator position cout << "The position of new iterator using next() is : "; cout << *it << " "; cout << endl; // Displaying iterator position cout << "The position of new iterator using prev() is : "; cout << *it1 << " "; cout << endl; return 0; }
Deque Library pop_front() Function in C++
Delete first element. Removes the first element in the deque container, effectively reducing its size by one. This destroys the removed element. The C++ deque::pop_front function is used to delete the first element of the deque. Every deletion of element results into reducing the container size by one unless the deque is empty. Removes the first element of the container. If there are no elements in the container, the behavior is undefined. Iterators and references to the erased element are invalidated. If the element is the last element in the container, the past-the-end iterator is also invalidated. Other references and iterators are not affected.
Syntax for Deque pop_front() Function in C++
#include <deque> void pop_front();
This function does not accept any parameter. This function does not return any value.
Complexity
Constant
Iterator validity
The iterators, pointers and references referring to the removed element are invalidated. Iterators, pointers and references referring to other elements that have not been removed are guaranteed to keep referring to the same elements they were referring to before the call.
Data races
The container is modified. The first element is modified. Concurrently accessing or modifying other elements is safe (although see iterator validity above).
Exception safety
If the container is not empty, the function never throws exceptions (no-throw guarantee). Otherwise, the behavior is undefined.
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/* deque pop_front() function is used to pop or remove elements from a deque from the front. The value is removed from the deque from the beginning, and the container size is decreased by 1. */ /* Delete first element by std::deque::pop_front function code example */ #include <iostream> #include <deque> using namespace std; int main (){ deque<int> MyDeque{100, 200, 300, 400, 500, 600}; deque<int>::iterator it; //deletes first element of the deque MyDeque.pop_front(); //deletes next first element of the deque MyDeque.pop_front(); cout<<"The deque contains:"; for(it = MyDeque.begin(); it != MyDeque.end(); ++it) cout<<" "<<*it; return 0; }
Deque Library at() Function in C++
Access element. Returns a reference to the element at position n in the deque container object. The function automatically checks whether n is within the bounds of valid elements in the container, throwing an out_of_range exception if it is not (i.e., if n is greater or equal than its size). This is in contrast with member operator[], that does not check against bounds. Returns a reference to the element at position n in the deque container object. The difference between this member function and member operator function operator[] is that deque::at signals if the requested position is out of range by throwing an out_of_range exception.
Syntax for Deque at() Function in C++
#include <deque> reference at (size_type n); const_reference at (size_type n) const;
n
Position of an element in the container. If this is greater than the deque size, an exception of type out_of_range is thrown. Notice that the first element has a position of 0 (not 1). Member type size_type is an unsigned integral type. Function returns the element at the specified position in the container. If the deque object is const-qualified, the function returns a const_reference. Otherwise, it returns a reference. Member types reference and const_reference are the reference types to the elements of the container (see deque member types).
Complexity
Constant
Iterator validity
No changes
Data races
The container is accessed (neither the const nor the non-const versions modify the container). Element n is potentially accessed or modified by the caller. Concurrently accessing or modifying other elements is safe.
Exception safety
Strong guarantee: if an exception is thrown, there are no changes in the container. It throws out_of_range if n is out of bounds.
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/* The C++ function std::deque::at() returns a reference to the element present at location n in the deque. */ /* access the element at specified position pos by Deque at() function code example. */ #include <iostream> #include <deque> int main () { std::deque<unsigned> mydeque (10); // 10 zero-initialized unsigneds // assign some values: for (unsigned i=0; i<mydeque.size(); i++) mydeque.at(i)=i; std::cout << "mydeque contains:"; for (unsigned i=0; i<mydeque.size(); i++) std::cout << ' ' << mydeque.at(i); std::cout << '\n'; return 0; }
Deque Library resize() Function in C++
Change size. Resizes the container so that it contains n elements. C++ Deque resize() function changes the size of the deque container to the size given in the argument. If n is smaller than the current container size, the content is reduced to its first n elements, removing those beyond (and destroying them). If n is greater than the current container size, the content is expanded by inserting at the end as many elements as needed to reach a size of n. If val is specified, the new elements are initialized as copies of val, otherwise, they are value-initialized. Notice that this function changes the actual content of the container by inserting or erasing elements from it.
Syntax for Deque resize() Function in C++
#include <deque> void resize (size_type n); void resize (size_type n, const value_type& val);
n
New container size, expressed in number of elements. Member type size_type is an unsigned integral type.
val
Object whose content is copied to the added elements in case that n is greater than the current container size. If not specified, the default constructor is used instead. Member type value_type is the type of the elements in the container, defined in deque as an alias of the first template parameter (T). This function does not return any value. In case of growth, the storage for the new elements is allocated using the container's allocator, which may throw exceptions on failure (for the default allocator, bad_alloc is thrown if the allocation request does not succeed).
Complexity
Linear on the number of elements inserted/erased (constructions/destructions).
Iterator validity
In case the container shrinks, all iterators, pointers and references to elements that have not been removed remain valid after the resize and refer to the same elements they were referring to before the call. If the container expands, all iterators are invalidated, but existing pointers and references remain valid, referring to the same elements they were referring to before.
Data races
The container is modified. Removed elements are modified (see iterator validity above).
Exception safety
If n is less than or equal to the size of the container, the function never throws exceptions (no-throw guarantee). Otherwise, if an exception is thrown, the container is left with a valid state (basic guarantee): Constructing elements or allocating storage may throw.
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/* The C++ function std::deque::resize() changes the size of deque. If n is smaller than current size then extra elements are destroyed. If n is greater than current container size then new elements are inserted at the end of deque. If val is specified then new elements are initialed with val. */ /* change the size of the deque container to the size given in the argument by Deque resize() function code example. */ #include <bits/stdc++.h> using namespace std; int main() { deque<int> dq = { 10, 20, 30, 40, 50 }; cout << "Size before resize " << dq.size() << "\n"; // Prints the deque elements cout << "The contents of deque :"; for (auto it = dq.begin(); it != dq.end(); ++it) cout << *it << " "; cout << endl; // resize to 7 dq.resize(7); // // Prints the deque elements after resize() cout << "Size after resize " << dq.size() << "\n"; cout << "The contents of deque :"; for (auto it = dq.begin(); it != dq.end(); ++it) cout << *it << " "; return 0; }
Deque Library push_front() Function in C++
Insert element at beginning. Inserts a new element at the beginning of the deque container, right before its current first element. The content of val is copied (or moved) to the inserted element. This effectively increases the container size by one. deque::push_front() is an inbuilt function in C++ STL which is declared in header file. deque::push_front() is used to push/insert an element at the front or at the beginning of the deque container making the pushed/inserted element as the first element of the deque. This function accepts one argument, that is, the element which is to be pushed/inserted at the beginning.
Syntax for Deque push_front() Function in C++
#include <deque> void push_front (const value_type& val); void push_front (value_type&& val);
val
Value to be copied (or moved) to the inserted element. Member type value_type is the type of the elements in the container, defined in deque as an alias of its first template parameter (T). This function does not return any value. The storage for the new elements is allocated using the container's allocator, which may throw exceptions on failure (for the default allocator, bad_alloc is thrown if the allocation request does not succeed).
Complexity
Constant
Iterator validity
All iterators related to this container are invalidated. Pointers and references to elements in the container remain valid, referring to the same elements they were referring to before the call.
Data races
The container is modified. No existing elements are accessed (although see iterator validity above).
Exception safety
Strong guarantee: if an exception is thrown, there are no changes in the container. If allocator_traits::construct is not supported with val as argument, it causes undefined behavior.
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/* push_front() function is used to push elements into a deque from the front. The new value is inserted into the deque at the beginning, before the current first element and the container size is increased by 1. */ // CPP program code example to illustrate application of push_front() function #include <deque> #include <iostream> using namespace std; int main() { int count = 0; deque<int> mydeque; mydeque.push_front(1); mydeque.push_front(2); mydeque.push_front(3); mydeque.push_front(4); mydeque.push_front(5); mydeque.push_front(6); while (!mydeque.empty()) { count++; mydeque.pop_front(); } cout << count; return 0; }
Deque Library rbegin() Function in C++
Return reverse iterator to reverse beginning. Returns a reverse iterator pointing to the last element in the container (i.e., its reverse beginning). Reverse iterators iterate backwards: increasing them moves them towards the beginning of the container. rbegin points to the element right before the one that would be pointed to by member end. Notice that unlike member deque::back, which returns a reference to this same element, this function returns a reverse random access iterator.
Syntax for Deque rbegin() Function in C++
#include <deque> reverse_iterator rbegin() noexcept; const_reverse_iterator rbegin() const noexcept;
This function does not accept any parameter. Function returns a reverse iterator to the reverse beginning of the sequence container. If the deque object is const-qualified, the function returns a const_reverse_iterator. Otherwise, it returns a reverse_iterator. Member types reverse_iterator and const_reverse_iterator are reverse random access iterator types (pointing to an element and to a const element, respectively). See deque member types.
Complexity
Constant
Iterator validity
No changes
Data races
The container is accessed (neither the const nor the non-const versions modify the container). No contained elements are accessed by the call, but the iterator returned can be used to access or modify elements. Concurrently accessing or modifying different elements is safe.
Exception safety
No-throw guarantee: this member function never throws exceptions. The copy construction or assignment of the returned iterator is also guaranteed to never throw.
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/* The C++ deque::rbegin function returns the reverse iterator pointing to the last element of the deque. A reverse iterator iterates in backward direction and increasing it results into moving to the beginning of the deque container. Similarly, decreasing a reverse iterator results into moving to the end of the deque container. Please note that, Unlike the deque::back function, which returns a direct reference to the last element, it returns the reverse iterator pointing to the same element of the deque. */ /* Return reverse iterator to reverse beginning by deque rbegin() function code example */ #include <iostream> #include <deque> using namespace std; int main (){ deque<string> MyDeque{"Alpha","Coding","Skills"}; deque<string>::reverse_iterator rit; rit = MyDeque.rbegin(); cout<<*rit<<" "; rit++; cout<<*rit<<" "; rit++; cout<<*rit<<" "; return 0; }
Deque Library assign() Function in C++
Assign container content. Assigns new contents to the deque container, replacing its current contents, and modifying its size accordingly. The deque::assign() is a built-in function in C++ STL which is used to assign values to the same or different deque container. On being called more than once in the same program, the function destroys the values of the previous elements and re-assigns new set of elements to the container. In the range version (1), the new contents are elements constructed from each of the elements in the range between first and last, in the same order. In the fill version (2), the new contents are n elements, each initialized to a copy of val. In the initializer list version (3), the new contents are copies of the values passed as initializer list, in the same order. If there are changes in storage, the internal allocator is used (through its traits). It is also used to destroy all existing elements, and to construct the new ones. Any elements held in the container before the call are destroyed and replaced by newly constructed elements (no assignments of elements take place).
Syntax for Deque assign() Function in C++
#include <deque> //range (1) template <class InputIterator> void assign (InputIterator first, InputIterator last); //fill (2) void assign (size_type n, const value_type& val); //initializer list (3) void assign (initializer_list<value_type> il);
first, last
Input iterators to the initial and final positions in a sequence. The range used is [first,last), which includes all the elements between first and last, including the element pointed by first but not the element pointed by last. The function template argument InputIterator shall be an input iterator type that points to elements of a type from which value_type objects can be constructed.
n
New size for the container. Member type size_type is an unsigned integral type.
val
Value to fill the container with. Each of the n elements in the container will be initialized to a copy of this value. Member type value_type is the type of the elements in the container, defined in deque as an alias of its first template parameter (T).
il
An initializer_list object. The compiler will automatically construct such objects from initializer list declarators. Member type value_type is the type of the elements in the container, defined in deque as an alias of its first template parameter (T). This function does not return any value.
Complexity
Linear in initial and final sizes (destructions, constructions).
Iterator validity
All iterators, pointers and references related to this container are invalidated.
Data races
All copied elements are accessed. The container is modified. All contained elements are modified.
Exception safety
Basic guarantee: if an exception is thrown, the container is in a valid state. If allocator_traits::construct is not supported with the appropriate arguments for the element constructions, or if the range specified by [first,last) is not valid, it causes undefined behavior.
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/* Deque is a double ended queue. In C++, deque::assign() is an inbuilt function which is used to assign the new value to the deque container. Every time this function is called it assigns a new value to the deque container by replacing the existing values and changing the size allocated accordingly. */ /* assign new contents to the deque container by deque::assign() function code example */ #include <bits/stdc++.h> using namespace std; int main() { deque<int> dq; // assign 5 values of 10 each dq.assign(5, 10); cout << "The deque elements: "; for (auto it = dq.begin(); it != dq.end(); it++) cout << *it << " "; deque<int> dq1; // assigns all elements from // the second position to deque1 dq1.assign(dq.begin() + 1, dq.end()); cout << "\nThe deque1 elements: "; for (auto it = dq1.begin(); it != dq1.end(); it++) cout << *it << " "; return 0; }
Deque Library max_size() Function in C++
Function returns the maximum number of elements that the deque container can hold. The deque::max_size() is a built-in function in C++ STL which returns the maximum number of elements that a deque container can hold. This is the maximum potential size the container can reach due to known system or library implementation limitations, but the container is by no means guaranteed to be able to reach that size: it can still fail to allocate storage at any point before that size is reached.
Syntax for Deque max_size() Function in C++
#include <deque> size_type max_size() const noexcept;
It does not contain any parameter. Function returns the maximum number of elements a deque container can hold as content. Member type size_type is an unsigned integral type.
Complexity
Constant
Iterator validity
No changes
Data races
The container is accessed. No contained elements are accessed: concurrently accessing or modifying them is safe.
Exception safety
No-throw guarantee: this member function never throws exceptions.
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/* The C++ deque::max_size function returns the maximum size the deque can reach. The function returns the maximum potential size the deque can reach due to known system or library implementation limitations. */ /* get maximum size of the deque by deque max_size() function code example */ #include <iostream> #include <deque> using namespace std; int main (){ deque<int> MyDeque{10, 20, 30, 40, 50}; deque<int>::iterator it; cout<<"The deque contains:"; for(it = MyDeque.begin(); it != MyDeque.end(); ++it) cout<<" "<<*it; cout<<"\nDeque size is: "<<MyDeque.size()<<"\n"; cout<<"Maximum size of the Deque: "<<MyDeque.max_size()<<"\n"; return 0; }
main() Function in C++
A program shall contain a global function named main, which is the designated start of the program in hosted environment. main() function is the entry point of any C++ program. It is the point at which execution of program is started. When a C++ program is executed, the execution control goes directly to the main() function. Every C++ program have a main() function.
Syntax for main() Function in C++
void main() { ............ ............ }
void
void is a keyword in C++ language, void means nothing, whenever we use void as a function return type then that function nothing return. here main() function no return any value.
main
main is a name of function which is predefined function in C++ library. In place of void we can also use int return type of main() function, at that time main() return integer type value. 1) It cannot be used anywhere in the program a) in particular, it cannot be called recursively b) its address cannot be taken 2) It cannot be predefined and cannot be overloaded: effectively, the name main in the global namespace is reserved for functions (although it can be used to name classes, namespaces, enumerations, and any entity in a non-global namespace, except that a function called "main" cannot be declared with C language linkage in any namespace). 3) It cannot be defined as deleted or (since C++11) declared with C language linkage, constexpr (since C++11), consteval (since C++20), inline, or static. 4) The body of the main function does not need to contain the return statement: if control reaches the end of main without encountering a return statement, the effect is that of executing return 0;. 5) Execution of the return (or the implicit return upon reaching the end of main) is equivalent to first leaving the function normally (which destroys the objects with automatic storage duration) and then calling std::exit with the same argument as the argument of the return. (std::exit then destroys static objects and terminates the program). 6) (since C++14) The return type of the main function cannot be deduced (auto main() {... is not allowed). 7) (since C++20) The main function cannot be a coroutine.
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/* simple code example by main() function in C++ */ #include <iostream> using namespace std; int main() { int day = 4; switch (day) { case 1: cout << "Monday"; break; case 2: cout << "Tuesday"; break; case 3: cout << "Wednesday"; break; case 4: cout << "Thursday"; break; case 5: cout << "Friday"; break; case 6: cout << "Saturday"; break; case 7: cout << "Sunday"; break; } return 0; }
Deque Library clear() Function in C++
Clear content. Removes all elements from the deque (which are destroyed), leaving the container with a size of 0. The C++ function std::deque::clear() destroys the deque by removing all elements from the deque and sets size of deque to zero. Erases all elements from the container. After this call, size() returns zero. Invalidates any references, pointers, or iterators referring to contained elements. Any past-the-end iterators are also invalidated.
Syntax for Deque clear() Function in C++
#include<deque> void clear() noexcept;
This function does not accept any parameter. This function does not return any value.
Complexity
Linear in size (destructions).
Iterator validity
All iterators, pointers and references related to this container are invalidated.
Data races
The container is modified. All contained elements are modified.
Exception safety
No-throw guarantee: this member function never throws exceptions.
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/* C++ Deque clear() function removes all the elements from the deque and the size of the deque is reduced to zero. */ /* remove all the elements from the deque by clear() function code example */ #include<iostream> #include<deque> using namespace std; int main() { deque<int> first; deque<int>::iterator itr; cout<<"Content of first deque:"; first.push_back(1); first.push_back(2); first.push_back(3); for(itr=first.begin();itr!=first.end();++itr) cout<<*itr<<" "; cout<<'\n'; first.clear(); cout<<"Now,Content of first deque:"; first.push_back(4); first.push_back(5); first.push_back(6); for(itr=first.begin();itr!=first.end();++itr) cout<<*itr<<" "; return 0; }
Deque Library push_back() Function in C++
Add element at the end. Adds a new element at the end of the deque container, after its current last element. The content of val is copied (or moved) to the new element. This effectively increases the container size by one. push_back() function is used to push elements into a deque from the back. The new value is inserted into the deque at the end, before the current last element and the container size is increased by 1.
Syntax for Deque push_back() Function in C++
#include <deque> void push_back (const value_type& val); void push_back (value_type&& val);
val
Value to be copied (or moved) to the new element. Member type value_type is the type of the elements in the container, defined in deque as an alias of its first template parameter (T). This function does not return any value. The storage for the new elements is allocated using the container's allocator, which may throw exceptions on failure (for the default allocator, bad_alloc is thrown if the allocation request does not succeed).
Complexity
Constant
Iterator validity
All iterators related to this container are invalidated. Pointers and references to elements in the container remain valid, referring to the same elements they were referring to before the call.
Data races
The container is modified. No existing elements are accessed (although see iterator validity above).
Exception safety
Strong guarantee: if an exception is thrown, there are no changes in the container. If allocator_traits::construct is not supported with val as argument, it causes undefined behavior.
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/* C++ Deque push_back() function adds a new element at the end of the deque container and the size of the container is increased by one. */ // C++ code example to demonstrate the working of deque push_back( ) function #include<iostream.h> #include<deque.h> Using namespace std; int main ( ){ // initializing the deque Deque<int> deque = { 71, 75, 73, 76, 77 }; // print the deque cout<< " Deque: "; for( auto x = deque.begin( ); x != deque.end( ); ++x) cout<< *x << " "; // defining the push_backt( ) function deque.push_back(78); // printing new deque after inserting new element for( x = deque.begin( ); x != deque.end( ); ++x) cout<< " " << *x; return 0; }
Deque Library begin() Function in C++
Return iterator to beginning. Returns an iterator pointing to the first element in the deque container. Notice that, unlike member deque::front, which returns a reference to the first element, this function returns a random access iterator pointing to it. If the container is empty, the returned iterator value shall not be dereferenced. deque::begin() is an inbuilt function in C++ STL which is declared in header file. deque::begin() returns an iterator which is referencing to the first element of the deque container associated with the function. Both begin() and end() are used to iterate through the deque container.
Syntax for Deque begin() Function in C++
#include <deque> iterator begin() noexcept; const_iterator begin() const noexcept;
This function does not accept any parameter. Function returns an iterator to the beginning of the sequence container. If the deque object is const-qualified, the function returns a const_iterator. Otherwise, it returns an iterator. Member types iterator and const_iterator are random access iterator types (pointing to an element and to a const element, respectively).
Complexity
Constant
Iterator validity
No changes.
Data races
The container is accessed (neither the const nor the non-const versions modify the container). No contained elements are accessed by the call, but the iterator returned can be used to access or modify elements. Concurrently accessing or modifying different elements is safe.
Exception safety
No-throw guarantee: this member function never throws exceptions. The copy construction or assignment of the returned iterator is also guaranteed to never throw.
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/* returns an iterator pointing to the first element in the deque container by std::deque::begin function code example. */ // CPP program to illustrate implementation of end() function #include <deque> #include <iostream> using namespace std; int main() { // declaration of deque container deque<int> mydeque{ 1, 2, 3, 4, 5 }; // using end() to print deque for (auto it = mydeque.begin(); it != mydeque.end(); ++it) cout << ' ' << *it; return 0; }
Deque Library front() Function in C++
Access first element. Returns a reference to the first element in the deque container. The C++ function std::deque::front() returns a reference to the first element of the deque. Unlike member deque::begin, which returns an iterator to this same element, this function returns a direct reference. Calling this function on an empty container causes undefined behavior.
Syntax for Deque front() Function in C++
#include <deque> reference front(); const_reference front() const;
No parameter is required. Function returns a reference to the first element in the deque container. If the deque object is const-qualified, the function returns a const_reference. Otherwise, it returns a reference. Member types reference and const_reference are the reference types to the elements of the container (see deque member types).
Complexity
Constant
Iterator validity
No changes
Data races
The container is accessed (neither the const nor the non-const versions modify the container). The first element is potentially accessed or modified by the caller. Concurrently accessing or modifying other elements is safe.
Exception safety
If the container is not empty, the function never throws exceptions (no-throw guarantee). Otherwise, it causes undefined behavior.
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/* front() is used to reference the first element of the deque container. This function can be used to fetch the first element of a deque. This is an inbuilt function from C++ Standard Template Library(STL). This function belongs to the <deque> header file. */ /* Access first element by std::deque::front function code example */ #include <iostream> #include <deque> using namespace std; int main (){ deque<int> MyDeque{10, 20, 30, 40, 50}; cout<<"The first element of MyDeque is: "; cout<<MyDeque.front(); cout<<"\n\nAdd 100 to the first element of the MyDeque.\n"; MyDeque.front() = MyDeque.front() + 100; cout<<"Now, The first element of MyDeque is: "; cout<<MyDeque.front(); return 0; }
Deque Library pop_back() Function in C++
Delete last element. Removes the last element in the deque container, effectively reducing the container size by one. pop_back() function is used to pop or remove elements from a deque from the back. The value is removed from the deque from the end, and the container size is decreased by 1. This destroys the removed element.
Syntax for Deque pop_back() Function in C++
#include <deque> void pop_back();
This function does not accept any parameter. This function does not return any value.
Complexity
Constant
Iterator validity
The end iterator and any iterator, pointer and reference referring to the removed element are invalidated. Iterators, pointers and references referring to other elements that have not been removed are guaranteed to keep referring to the same elements they were referring to before the call.
Data races
The container is modified. The last element is modified. Concurrently accessing or modifying other elements is safe (although see iterator validity above).
Exception safety
If the container is not empty, the function never throws exceptions (no-throw guarantee). Otherwise, the behavior is undefined.
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/* The C++ deque::pop_back function is used to delete the last element of the deque. Every deletion of element results into reducing the container size by one unless the deque is empty. */ /* Delete last element by deque pop_back() function code example */ #include <iostream> #include <deque> using namespace std; int main (){ deque<int> MyDeque{100, 200, 300, 400, 500, 600}; deque<int>::iterator it; //deletes last element of the deque MyDeque.pop_back(); //deletes next last element of the deque MyDeque.pop_back(); cout<<"The deque contains:"; for(it = MyDeque.begin(); it != MyDeque.end(); ++it) cout<<" "<<*it; return 0; }
Deque Library rend() Function in C++
Return reverse iterator to reverse end. Returns a reverse iterator pointing to the theoretical element preceding the first element in the deque container (which is considered its reverse end). The deque::rend() is an inbuilt function in C++ STL which returns a reverse iterator which points to the position before the beginning of the deque (which is considered its reverse end). The range between deque::rbegin and deque::rend contains all the elements of the deque container (in reverse order).
Syntax for Deque rend() Function in C++
#include <deque> reverse_iterator rend() noexcept; const_reverse_iterator rend() const noexcept;
This function does not accept any parameter. Function returns a reverse iterator to the reverse end of the sequence container. If the deque object is const-qualified, the function returns a const_reverse_iterator. Otherwise, it returns a reverse_iterator. Member types reverse_iterator and const_reverse_iterator are reverse random access iterator types (pointing to an element and to a const element, respectively). See deque member types.
Complexity
Constant
Iterator validity
No changes
Data races
The container is accessed (neither the const nor the non-const versions modify the container). No contained elements are accessed by the call, but the iterator returned can be used to access or modify elements. Concurrently accessing or modifying different elements is safe.
Exception safety
No-throw guarantee: this member function never throws exceptions. The copy construction or assignment of the returned iterator is also guaranteed to never throw.
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/* The C++ deque::rend function returns the reverse iterator pointing to the element preceding the first element (reversed past-the-last element) of the deque. A reverse iterator iterates in backward direction and increasing it results into moving to the beginning of the deque container. Similarly, decreasing a reverse iterator results into moving to the end of the deque container. */ /* Return reverse iterator to reverse end by deque rend() function code example */ #include <iostream> #include <deque> using namespace std; int main(void) { deque<int> d = {1, 2, 3, 4, 5}; cout << "Contents of deque are" << endl; for (auto it = d.rend() - 1; it >= d.rbegin(); --it) cout << *it << endl; return 0; }
If Else Statement in C++
In computer programming, we use the if statement to run a block code only when a certain condition is met. An if statement can be followed by an optional else statement, which executes when the boolean expression is false. There are three forms of if...else statements in C++: • if statement, • if...else statement, • if...else if...else statement,
Syntax for If Statement in C++
if (condition) { // body of if statement }
The if statement evaluates the condition inside the parentheses ( ). If the condition evaluates to true, the code inside the body of if is executed. If the condition evaluates to false, the code inside the body of if is skipped.
Syntax for If...Else Statement
if (condition) { // block of code if condition is true } else { // block of code if condition is false }
The if..else statement evaluates the condition inside the parenthesis. If the condition evaluates true, the code inside the body of if is executed, the code inside the body of else is skipped from execution. If the condition evaluates false, the code inside the body of else is executed, the code inside the body of if is skipped from execution. The if...else statement is used to execute a block of code among two alternatives. However, if we need to make a choice between more than two alternatives, we use the if...else if...else statement.
Syntax for If...Else...Else If Statement in C++
if (condition1) { // code block 1 } else if (condition2){ // code block 2 } else { // code block 3 }
• If condition1 evaluates to true, the code block 1 is executed. • If condition1 evaluates to false, then condition2 is evaluated. • If condition2 is true, the code block 2 is executed. • If condition2 is false, the code block 3 is executed. There can be more than one else if statement but only one if and else statements. In C/C++ if-else-if ladder helps user decide from among multiple options. The C/C++ if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the C else-if ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.
Syntax for If Else If Ladder in C++
if (condition) statement 1; else if (condition) statement 2; . . else statement;
Working of the if-else-if ladder: 1. Control falls into the if block. 2. The flow jumps to Condition 1. 3. Condition is tested. If Condition yields true, goto Step 4. If Condition yields false, goto Step 5. 4. The present block is executed. Goto Step 7. 5. The flow jumps to Condition 2. If Condition yields true, goto step 4. If Condition yields false, goto Step 6. 6. The flow jumps to Condition 3. If Condition yields true, goto step 4. If Condition yields false, execute else block. Goto Step 7. 7. Exits the if-else-if ladder. • The if else ladder statement in C++ programming language is used to check set of conditions in sequence. • This is useful when we want to selectively executes one code block(out of many) based on certain conditions. • It allows us to check for multiple condition expressions and execute different code blocks for more than two conditions. • A condition expression is tested only when all previous if conditions in if-else ladder is false. • If any of the conditional expression evaluates to true, then it will execute the corresponding code block and exits whole if-else ladder.
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/* If Else Statement in C++ Language */ #include <iostream> using namespace std; int main () { // local variable declaration: int a = 100; // check the boolean condition if( a < 20 ) { // if condition is true then print the following cout << "a is less than 20;" << endl; } else { // if condition is false then print the following cout << "a is not less than 20;" << endl; } cout << "value of a is : " << a << endl; return 0; }
Deque Library get_allocator() Function in C++
Get allocator. Returns a copy of the allocator object associated with the deque object. public member function std::deque::get_allocator gets allocator. deque::get_allocator() is a built in function in C++ STL which is used to get allocator of container deque.
Syntax for Deque get_allocator() Function in C++
#include <deque> allocator_type get_allocator() const noexcept;
This function does not accept any parameter. Function returns the allocator. Member type allocator_type is the type of the allocator used by the container, defined in deque as an alias of its second template parameter (Alloc).
Complexity
Constant
Iterator validity
No changes
Data races
The container is accessed. No contained elements are accessed: concurrently accessing or modifying them is safe.
Exception safety
No-throw guarantee: this member function never throws exceptions. Copying any instantiation of the default allocator is also guaranteed to never throw.
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/* The C++ deque::get_allocator function returns a copy of allocator object associated with the given deque. */ /* Get allocator by deque get_allocator function code example */ #include <iostream> #include <deque> using namespace std; int main (){ deque<int> MyDeque; int *p; //allocate array with a memory to store 5 //elements using deque's allocator p = MyDeque.get_allocator().allocate(5); //construct values in-place on the array for(int i=0; i<5; i++) MyDeque.get_allocator().construct(&p[i], 100*(i+1)); cout<<"The allocated array contains: "; for(int i=0; i<5; i++) cout<<p[i]<<" "; //destroy and deallocate the array for(int i=0; i<5; i++) MyDeque.get_allocator().destroy(&p[i]); MyDeque.get_allocator().deallocate(p,5); return 0; }
Deque Library insert() Function in C++
Insert elements. The deque container is extended by inserting new elements before the element at the specified position. This effectively increases the container size by the amount of elements inserted. C++ Deque insert() function inserts new element just before the specified position pos and the size of the container increases by the number of elements are inserted. Insertion of an element can be done either from front or from the back. Double-ended queues are designed to be efficient performing insertions (and removals) from either the end or the beginning of the sequence. Insertions on other positions are usually less efficient than in list or forward_list containers. The parameters determine how many elements are inserted and to which values they are initialized:
Syntax for Deque insert() Function in C++
#include <deque> //single element (1) iterator insert (const_iterator position, const value_type& val); //fill (2) iterator insert (const_iterator position, size_type n, const value_type& val); //range (3) template <class InputIterator> iterator insert (const_iterator position, InputIterator first, InputIterator last); //move (4) iterator insert (const_iterator position, value_type&& val); //initializer list (5) iterator insert (const_iterator position, initializer_list<value_type> il);
position
Position in the container where the new elements are inserted. iterator is a member type, defined as a random access iterator type that points to elements.
val
Value to be copied (or moved) to the inserted elements. Member type value_type is the type of the elements in the container, defined in deque as an alias of its first template parameter (T).
n
Number of elements to insert. Each element is initialized to a copy of val. Member type size_type is an unsigned integral type.
first, last
Iterators specifying a range of elements. Copies of the elements in the range [first,last) are inserted at position (in the same order). Notice that the range includes all the elements between first and last, including the element pointed by first but not the one pointed by last. The function template argument InputIterator shall be an input iterator type that points to elements of a type from which value_type objects can be constructed.
il
An initializer_list object. Copies of these elements are inserted at position (in the same order). These objects are automatically constructed from initializer list declarators. Member type value_type is the type of the elements in the container, defined in deque as an alias of its first template parameter (T). Function returns an iterator that points to the first of the newly inserted elements. Member type iterator is a random access iterator type that points to elements. The storage for the new elements is allocated using the container's allocator, which may throw exceptions on failure (for the default allocator, bad_alloc is thrown if the allocation request does not succeed).
Complexity
Linear on the number of elements inserted (copy/move construction). Plus, depending on the particular library implemention, up to an additional linear in the number of elements between position and one of the ends of the deque.
Iterator validity
If the insertion happens at the beginning or the end of the sequence, all iterators related to this container are invalidated, but pointers and references remain valid, referring to the same elements they were referring to before the call. If the insertion happens anywhere else in the deque, all iterators, pointers and references related to this container are invalidated.
Data races
The container is modified. If the insertion happens at the beginning or the end of the sequence, no contained elements are accessed (although see iterator validity above). If it happens anywhere else, it is not safe to concurrently access elements.
Exception safety
If the operation inserts a single element at the begin or the end, there are no changes in the container in case of exception (strong guarantee). Otherwise, the container is guaranteed to end in a valid state (basic guarantee). If allocator_traits::construct is not supported with the appropriate arguments for the element constructions, or if an invalid position or range is specified, it causes undefined behavior.
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/* insert new elements before the element at the specified position by deque::insert function code example. */ #include <iostream> #include <deque> using namespace std; int main (){ deque<int> deque1 = {10, 20, 30}; deque<int> deque2 = {10, 20, 30}; deque<int> deque3 = {10, 20, 30}; deque<int> deque4 = {100, 200, 300}; deque<int>::iterator it; //single element version it = deque1.begin(); deque1.insert(it + 2, 55); //fill version - fill 3 new elements at specified location it = deque2.begin(); deque2.insert(it + 2, 3, 55); //range version it = deque3.begin(); deque3.insert(it+2, deque4.begin(), deque4.end()); cout<<"deque1 contains: "; for(it = deque1.begin(); it != deque1.end(); ++it) cout<<*it<<" "; cout<<"\ndeque2 contains: "; for(it = deque2.begin(); it != deque2.end(); ++it) cout<<*it<<" "; cout<<"\ndeque3 contains: "; for(it = deque3.begin(); it != deque3.end(); ++it) cout<<*it<<" "; return 0; }
Deque Library erase() Function in C++
Erase elements. Removes from the deque container either a single element (position) or a range of elements ([first,last)). C++ Deque erase() function removes the element from the specified position or range and this effectively reduces the size of the deque by the number of elements removed. This effectively reduces the container size by the number of elements removed, which are destroyed. Double-ended queues are designed to be efficient removing (and inserting) elements at either the end or the beginning of the sequence. Removals on other positions are usually less efficient than in list or forward_list containers.
Syntax for Deque erase() Function in C++
#include <deque> iterator erase (const_iterator position ); iterator erase (const_iterator first, const_iterator last );
position
Iterator pointing to a single element to be removed from the deque. Member types iterator and const_iterator are random access iterator types that point to elements.
first, last
Iterators specifying a range within the deque] to be removed: [first,last). i.e., the range includes all the elements between first and last, including the element pointed by first but not the one pointed by last. Member types iterator and const_iterator are random access iterator types that point to elements. Function returns an iterator pointing to the new location of the element that followed the last element erased by the function call. This is the container end if the operation erased the last element in the sequence. Member type iterator is a random access iterator type that points to elements.
Complexity
Linear on the number of elements erased (destructions). Plus, depending on the particular library implemention, up to an additional linear time on the number of elements between position and one of the ends of the deque.
Iterator validity
If the erasure operation includes the last element in the sequence, the end iterator and the iterators, pointers and references referring to the erased elements are invalidated. If the erasure includes the first element but not the last, only those referring to the erased elements are invalidated. If it happens anywhere else in the deque, all iterators, pointers and references related to the container are invalidated.
Data races
The container is modified. If the erasure happens at the beginning or the end of the sequence, only the erased elements are modified (although see iterator validity above). If it happens anywhere else, it is not safe to access or modify elements.
Exception safety
If the removed elements include the first or the last element in the container, no exceptions are thrown (no-throw guarantee). Otherwise, the container is guaranteed to end in a valid state (basic guarantee): Copying or moving elements while relocating them may throw. Invalid ranges produce undefined behavior.
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/* deque erase() function is used to remove the element from the container at specified position and in a range. This function reduces the size of the deque container by the number of elements removed. Deque containers are efficient in removing or inserting the elements at the beginning or at the end of the deque container. */ /* remove elements from a container from the specified position or range by deque erase() function code example. */ #include <deque> #include <iostream> using namespace std; int main() { deque<int> mydeque{ 1, 2, 3, 4, 5, 6, 7, 8, 9 }; deque<int>::iterator i; i = mydeque.begin(); while (i != mydeque.end()) { if (*i % 2 == 0) /* Not a good idea to erase inside loop, if you delete last element, mydeque.end() cannot be found resulting in infinite loop */ mydeque.erase(i); i++; } // Printing the deque for (auto it = mydeque.begin(); it != mydeque.end(); ++it) cout << ' ' << *it; return 0; }
Deque in C++ Language
deque (usually pronounced like "deck") is an irregular acronym of double-ended queue. Double-ended queues are sequence containers with dynamic sizes that can be expanded or contracted on both ends (either its front or its back). Specific libraries may implement deques in different ways, generally as some form of dynamic array. But in any case, they allow for the individual elements to be accessed directly through random access iterators, with storage handled automatically by expanding and contracting the container as needed. Therefore, they provide a functionality similar to vectors, but with efficient insertion and deletion of elements also at the beginning of the sequence, and not only at its end. But, unlike vectors, deques are not guaranteed to store all its elements in contiguous storage locations: accessing elements in a deque by offsetting a pointer to another element causes undefined behavior. Both vectors and deques provide a very similar interface and can be used for similar purposes, but internally both work in quite different ways: While vectors use a single array that needs to be occasionally reallocated for growth, the elements of a deque can be scattered in different chunks of storage, with the container keeping the necessary information internally to provide direct access to any of its elements in constant time and with a uniform sequential interface (through iterators). Therefore, deques are a little more complex internally than vectors, but this allows them to grow more efficiently under certain circumstances, especially with very long sequences, where reallocations become more expensive. For operations that involve frequent insertion or removals of elements at positions other than the beginning or the end, deques perform worse and have less consistent iterators and references than lists and forward lists.
Syntax for Deque in C++
#include <deque> template < class T, class Alloc = allocator<T> > class deque;
T
Type of the elements. Aliased as member type deque::value_type.
Alloc
Type of the allocator object used to define the storage allocation model. By default, the allocator class template is used, which defines the simplest memory allocation model and is value-independent. Aliased as member type deque::allocator_type. Sequence: Elements in sequence containers are ordered in a strict linear sequence. Individual elements are accessed by their position in this sequence. Dynamic array: Generally implemented as a dynamic array, it allows direct access to any element in the sequence and provides relatively fast addition/removal of elements at the beginning or the end of the sequence. Allocator-aware: The container uses an allocator object to dynamically handle its storage needs.
Initialize a Deque in C++
// method 1: initializer list deque<int> deque1 = {1, 2, 3, 4, 5}; // method 2: uniform initialization deque<int> deque2 {1, 2, 3, 4, 5};
Deque Member Types
• value_type T (First template parameter) • allocator_type Alloc (Second template parameter), default: allocator<value_type> • reference value_type& • const_reference const value_type& • pointer Alloc::pointer, default: value_type* • const_pointer Alloc::const_pointer, default: value_type* • iterator a random access iterator to value_type • const_iterator a random access iterator to const value_type • reverse_iterator reverse_iterator <iterator> • const_reverse_iterator reverse_iterator <const_iterator> • difference_type ptrdiff_t • size_type size_t
C++ Deque Functions
• deque() Construct a deque object. • ~deque() Destroys container by deallocating container memory. • operator=() Assign content to a deque. • empty() Checks whether the deque is empty or not. • size() Returns the length of the deque in terms of bytes. • max_size() Returns the maximum length of the deque. • resize() Changes the size of the deque by specified number of elements. • shrink_to_fit() Reduces the capacity of the deque equal to fit its size. • at() Access an element of the deque. • operator[]() Access an element of the deque. • front() Access first element of the deque. • back() Access last element of the deque. • begin() Returns iterator pointing to the first element of the deque. • end() Returns iterator pointing to the past-the-last element of the deque. • rbegin() Returns reverse iterator to the last element of the deque. • rend() Returns reverse iterator to the element preceding the first element of the deque. • cbegin() Returns const_iterator pointing to the first element of the deque. • cend() Returns const_iterator pointing to the past-the-last element of the deque. • crbegin() Returns const_reverse_iterator to the last element of the deque. • crend() Returns const_reverse_iterator to the element preceding the first element of the deque. • assign() Assign deque content. • clear() Clears all elements of the deque. • pop_front() Deletes first element of the deque. • push_front() Adds a new element at the beginning of the deque. • pop_back() Deletes last element of the deque. • push_back() Adds a new element at the end of the deque. • insert() Insert elements in the deque. • erase() Deletes either a single element or range of elements from a deque. • emplace() Constructs and inserts a new element at specified position in the deque • emplace_front() Constructs and inserts a new element at the beginning of the deque. • emplace_back() Constructs and inserts a new element at the end of the deque. • swap() Exchanges elements between two deques. • get_allocator() Return a copy of allocator object associated with the deque. • operator == Checks whether two deques are equal or not. • operator != Checks whether two deques are unequal or not. • operator < Checks whether the first deque is less than the other or not. • operator > Checks whether the first deque is greater than the other or not. • operator <= Checks whether the first deque is less than or equal to the other or not. • operator >= Checks whether the first deque is greater than or equal to the other or not. • swap() Exchanges elements between two deques.
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/* In C++, the STL deque is a sequential container that provides the functionality of a double-ended queue data structure. */ #include <iostream> #include <deque> using namespace std; // function prototype void display_deque(deque<int>); int main() { // uniform initialization deque<int> deque1 {1, 2, 3, 4, 5}; cout << "deque1 = "; // display elements of deque1 for (int num : deque1) { cout << num << ", "; } return 0; }
Deque Library swap() Function in C++
Swap content. Exchanges the content of the container by the content of x, which is another deque object containing elements of the same type. Sizes may differ. After the call to this member function, the elements in this container are those which were in x before the call, and the elements of x are those which were in this. All iterators, references and pointers remain valid for the swapped objects. Notice that a non-member function exists with the same name, swap, overloading that algorithm with an optimization that behaves like this member function.
Syntax for Deque swap() Function in C++
#include <deque> void swap (deque& x);
x
Another deque container of the same type (i.e., instantiated with the same template parameters, T and Alloc) whose content is swapped with that of this container. This function does not return any value. Whether the container allocators are also swapped is not defined, unless in the case the appropriate allocator trait indicates explicitly that they shall propagate.
Complexity
Constant
Iterator validity
All iterators, pointers and references referring to elements in both containers remain valid, and are now referring to the same elements they referred to before the call, but in the other container, where they now iterate. Note that the end iterators do not refer to elements and may be invalidated.
Data races
Both the container and x are modified. No contained elements are accessed by the call (although see iterator validity above).
Exception safety
If the allocators in both containers compare equal, or if their allocator traits indicate that the allocators shall propagate, the function never throws exceptions (no-throw guarantee). Otherwise, it causes undefined behavior.
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/* C++ Deque swap() function exchanges the content of a given deque with the deque passed in the parameter of same type. */ /* exchange the contents of the first deque with another by std::deque::swap() function code example. */ #include <deque> #include <iostream> using namespace std; int main() { // deque container declaration deque<int> mydeque1{ 1, 2, 3, 4 }; deque<int> mydeque2{ 3, 5, 7, 9 }; // using swap() function to swap elements of deques mydeque1.swap(mydeque2); // printing the first deque cout << "mydeque1 = "; for (auto it = mydeque1.begin(); it < mydeque1.end(); ++it) cout << *it << " "; // printing the second deque cout << endl << "mydeque2 = "; for (auto it = mydeque2.begin(); it < mydeque2.end(); ++it) cout << *it << " "; return 0; }
Deque Library back() Function in C++
Access last element. Returns a reference to the last element in the container. The C++ function std::deque::back() returns a reference to the last element of the deque. Calling this function on empty causes undefined behavior. Unlike member deque::end, which returns an iterator just past this element, this function returns a direct reference. Calling this function on an empty container causes undefined behavior.
Syntax for Deque back() Function in C++
#include <deque> reference back(); const_reference back() const;
It does not contain any parameter. Function returns a reference to the last element in the deque container. If the deque object is const-qualified, the function returns a const_reference. Otherwise, it returns a reference. Member types reference and const_reference are the reference types to the elements of the container (see deque member types).
Complexity
Constant
Iterator validity
No changes
Data races
The container is accessed (neither the const nor the non-const versions modify the container). The last element is potentially accessed or modified by the caller. Concurrently accessing or modifying other elements is safe.
Exception safety
If the container is not empty, the function never throws exceptions (no-throw guarantee). Otherwise, it causes undefined behavior.
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/* back() function is used to reference the last element of the deque container. This function can be used to fetch the first element from the back of a deque. This function can be used to fetch the first element of a deque. This is an inbuilt function from C++ Standard Template Library(STL). This function belongs to the <deque> header file. */ /* Access last element by std::deque::back function code example */ // CPP program code example to illustrate application Of front() and back() function #include <deque> #include <iostream> using namespace std; int main() { deque<int> mydeque; mydeque.push_back(4); mydeque.push_back(3); mydeque.push_back(2); mydeque.push_back(1); // deque becomes 1, 2, 3, 4, if (mydeque.front() > mydeque.back()) { cout << mydeque.front() - mydeque.back(); } else if (mydeque.front() < mydeque.back()) { cout << mydeque.back() - mydeque.front(); } else cout << "0"; }
Iterator Library reverse_iterator in C++
This class reverses the direction in which a bidirectional or random-access iterator iterates through a range. A copy of the original iterator (the base iterator) is kept internally and used to reflect the operations performed on the reverse_iterator: whenever the reverse_iterator is incremented, its base iterator is decreased, and vice versa. A copy of the base iterator with the current state can be obtained at any time by calling member base. Notice however that when an iterator is reversed, the reversed version does not point to the same element in the range, but to the one preceding it. This is so, in order to arrange for the past-the-end element of a range: An iterator pointing to a past-the-end element in a range, when reversed, is pointing to the last element (not past it) of the range (this would be the first element of the reversed range). And if an iterator to the first element in a range is reversed, the reversed iterator points to the element before the first element (this would be the past-the-end element of the reversed range).
Syntax for reverse_iterator in C++
#include <iterator> template <class Iterator> class reverse_iterator;
Iterator
A bidirectional iterator type. Or a random-access iterator, if an operator that requires such a category of iterators is used.
Member types
• iterator_type Iterator Iterator's type • iterator_category iterator_traits<Iterator>::iterator_category Preserves Iterator's category • value_type iterator_traits<Iterator>::value_type Preserves Iterator's value type • difference_type iterator_traits<Iterator>::difference_type Preserves Iterator's difference type • pointer iterator_traits<Iterator>::pointer Preserves Iterator's pointer type • reference iterator_traits<Iterator>::reference Preserves Iterator's reference type
Member functions
• (constructor) Constructs reverse_iterator object (public member function ) • base Return base iterator (public member function ) • operator* Dereference iterator (public member function ) • operator+ Addition operator (public member function ) • operator++ Increment iterator position (public member function ) • operator+= Advance iterator (public member function ) • operator- Subtraction operator (public member function ) • operator-- Decrease iterator position (public member function ) • operator-= Retrocede iterator (public member function ) • operator-> Dereference iterator (public member function ) • operator[] Dereference iterator with offset (public member function )
Non-member function overloads
• relational operators Relational operators for reverse_iterator (function template ) • operator+ Addition operator (function template ) • operator- Subtraction operator (function template )
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/* std::reverse_iterator is an iterator adaptor that reverses the direction of a given iterator. In other words, when provided with a bidirectional iterator, std::reverse_iterator produces a new iterator that moves from the end to the beginning of the sequence defined by the underlying bidirectional iterator. */ /* Constructs reverse_iterator object by std::reverse_iterator */ #include <iostream> #include <iterator> template<typename T, size_t SIZE> class Stack { T arr[SIZE]; size_t pos = 0; public: T pop() { return arr[--pos]; } Stack& push(const T& t) { arr[pos++] = t; return *this; } // we wish that looping on Stack would be in LIFO order // thus we use std::reverse_iterator as an adaptor to existing iterators // (which are in this case the simple pointers: [arr, arr+pos) auto begin() { return std::reverse_iterator(arr + pos); } auto end() { return std::reverse_iterator(arr); } }; int main() { Stack<int, 8> s; s.push(5).push(15).push(25).push(35); for(int val: s) { std::cout << val << ' '; } }
Deque Library size() Function in C++
Return size. Returns the number of elements in the deque container. deque::size() is an inbuilt function in C++ STL which is declared in header file. deque::size() returns the size of the deque container associated with the function. If the container has no elements then the function returns 0. size() function is used to return the size of the deque container or the number of elements in the deque container. This is an inbuilt function from C++ Standard Template Library(STL). This function belongs to the <deque> header file. The function either returns a number demonstrating the total elements the deque holds at that instance.
Syntax for Deque size() Function in C++
#include <deque> size_type size() const noexcept;
This function does not accept any parameter. Function returns the number of elements in the container. Member type size_type is an unsigned integral type.
Complexity
Constant
Iterator validity
No changes
Data races
The container is accessed. No contained elements are accessed: concurrently accessing or modifying them is safe.
Exception safety
No-throw guarantee: this member function never throws exceptions.
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/* C++ Deque size() function determines the number of elements present in the deque container. */ // CPP program code example to demonstrate implementation of Deque size() function #include <deque> #include <iostream> using namespace std; // Driver Code int main() { int sum = 0; deque<int> mydeque; mydeque.push_back(1); mydeque.push_back(8); mydeque.push_back(3); mydeque.push_back(6); mydeque.push_back(2); // deque becomes 1, 8, 3, 6, 2 cout << mydeque.size(); return 0; }
Deque Library end() Function in C++
Return iterator to end. Returns an iterator referring to the past-the-end element in the deque container. The past-the-end element is the theoretical element that would follow the last element in the deque container. It does not point to any element, and thus shall not be dereferenced. Because the ranges used by functions of the standard library do not include the element pointed by their closing iterator, this function is often used in combination with deque::begin to specify a range including all the elements in the container. If the container is empty, this function returns the same as deque::begin. deque::end() is an inbuilt function in C++ STL which is declared in<deque> header file. deque::end() returns an iterator which is referencing next to the last element of the deque container associated with the function. Both begin() and end() are used to iterate through the deque container.
Syntax for Deque end() Function in C++
#include <deque> iterator end() noexcept; const_iterator end() const noexcept;
This function does not accept any parameter. Function returns an iterator to the element past the end of the sequence. If the deque object is const-qualified, the function returns a const_iterator. Otherwise, it returns an iterator. Member types iterator and const_iterator are random access iterator types (pointing to an element and to a const element, respectively).
Complexity
Constant
Iterator validity
No changes
Data races
The container is accessed (neither the const nor the non-const versions modify the container). No contained elements are accessed by the call, but the iterator returned can be used to access or modify elements. Concurrently accessing or modifying different elements is safe.
Exception safety
No-throw guarantee: this member function never throws exceptions. The copy construction or assignment of the returned iterator is also guaranteed to never throw.
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/* returns a random access iterator which points to the last element of the deque by std::deque::end() function code example. */ // CPP program to illustrate implementation of end() function #include <deque> #include <iostream> using namespace std; int main() { // declaration of deque container deque<int> mydeque{ 1, 2, 3, 4, 5 }; // using end() to print deque for (auto it = mydeque.begin(); it != mydeque.end(); ++it) cout << ' ' << *it; return 0; }
#include Directive in C++
#include is a way of including a standard or user-defined file in the program and is mostly written at the beginning of any C/C++ program. This directive is read by the preprocessor and orders it to insert the content of a user-defined or system header file into the following program. These files are mainly imported from an outside source into the current program. The process of importing such files that might be system-defined or user-defined is known as File Inclusion. This type of preprocessor directive tells the compiler to include a file in the source code program.
Syntax for #include Directive in C++
#include "user-defined_file"
Including using " ": When using the double quotes(" "), the preprocessor access the current directory in which the source "header_file" is located. This type is mainly used to access any header files of the user's program or user-defined files.
#include <header_file>
Including using <>: While importing file using angular brackets(<>), the the preprocessor uses a predetermined directory path to access the file. It is mainly used to access system header files located in the standard system directories. Header File or Standard files: This is a file which contains C/C++ function declarations and macro definitions to be shared between several source files. Functions like the printf(), scanf(), cout, cin and various other input-output or other standard functions are contained within different header files. So to utilise those functions, the users need to import a few header files which define the required functions. User-defined files: These files resembles the header files, except for the fact that they are written and defined by the user itself. This saves the user from writing a particular function multiple times. Once a user-defined file is written, it can be imported anywhere in the program using the #include preprocessor. • In #include directive, comments are not recognized. So in case of #include <a//b>, a//b is treated as filename. • In #include directive, backslash is considered as normal text not escape sequence. So in case of #include <a\nb>, a\nb is treated as filename. • You can use only comment after filename otherwise it will give error.
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/* using #include directive in C language */ #include <stdio.h> int main() { /* * C standard library printf function * defined in the stdio.h header file */ printf("I love you Clementine"); printf("I love you so much"); printf("HappyCodings"); return 0; }


C++ program, "using iteration", implements the list of elements removed from the queue in first in first out mode using a Linked list. A linked list is an ordered set of data elements,
To convert a number from "hexadecimal" into equivalent decimal format "in C++", enter the hexadecimal number to convert it to decimal to display the equivalent value in "decimal" as