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C++ Programming Code Examples

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Use find the search an element in deque

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/* Use find the search an element in deque */ #include <iostream> #include <cassert> #include <deque> #include <algorithm> // For find using namespace std; int main() { int x[5] = {1, 2, 3, 4, 5}; deque<int> deque1(&x[0], &x[5]); // Search for the first occurrence deque<int>::iterator where = find(deque1.begin(), deque1.end(), 1); cout << *where << endl; return 0; } /* 1 */
Algorithm Library find() Function in C++
C++ find() function is part of the standard library function which tries to find the first occurrence of the specified range of element where the range starts with first range to last range and that iterator encounters the first element, compares for the value which must be equal after all possible comparisons and if no element is found it returns the last element. For making all the comparisons it makes use of the operator = for comparison. If find() function performs any unnecessary action it throws exceptions that are not required by the programmer. Find value in range. Returns an iterator to the first element in the range [first,last) that compares equal to val. If no such element is found, the function returns last. The function uses operator== to compare the individual elements to val.
Syntax for find() Function in C++
template <class InputIterator, class T> InputIterator find (InputIterator first, InputIterator last, const T& val);
first
Input iterator to the initial position.
last
Input iterator to the final position. Input iterators to the initial and final positions in a sequence. The range searched is [first,last), which contains all the elements between first and last, including the element pointed by first but not the element pointed by last.
val
Value to compare the elements. Value to search for in the range. T shall be a type supporting comparisons with the elements pointed by InputIterator using operator== (with the elements as left-hand side operands, and val as right-hand side). Function returns an iterator to the first element in the range that compares equal to val. If no elements match, the function returns last. If element found it returns an iterator pointing to the first occurrence of the element otherwise returns last. Throws exception if either element comparison or an operation on an iterator throws exception. Please note that invalid parameters cause undefined behavior. Any find() function defined should have a proper standard library for inclusion otherwise it will throw an unwanted exception saying that this member or method is not present with the designated standard library for the function which means incompatibility of function with the standard library. Advantages of C++ algorithm library find() function: • find() function as part of the standard library can be used by the programmers for searching elements at the time of comparison with the first and last element within a specified range. • The iterator pointing to the first or the last element can enhance or manipulate the entire traversal process as all the elements present are with the index were retrieving the value is important for comparisons and other operations. • It enhances the reusability of the code base as it not important to design and define a function again and again wherever required we can call the find function and the task becomes simplified as it will be already present within the standard library. • Testing of individual functions becomes easy as the scope for re-writing function becomes simplified. • The division of the program makes the view of the codebase clear and understandable by the programmers to write a new and enhanced form of code.
Complexity
Up to linear in the distance between first and last: Compares elements until a match is found.
Data races
Some (or all) of the objects in the range [first,last) are accessed (once at most).
Exceptions
Throws if either an element comparison or an operation on an iterator throws. Note that invalid arguments cause undefined behavior.
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/* algorithm library find() function in C++ language */ #include <iostream> #include <vector> #include <algorithm> using namespace std; int main(void) { int val = 5; vector<int> v = {1, 2, 3, 4, 5}; auto result = find(v.begin(), v.end(), val); if (result != end(v)) cout << "Vector contains element " << val << endl; val = 15; result = find(v.begin(), v.end(), val); if (result == end(v)) cout << "Vector doesn't contain element " << val << endl; 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 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; }
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 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; }
Namespaces in C++ Language
Consider a situation, when we have two persons with the same name, jhon, in the same class. Whenever we need to differentiate them definitely we would have to use some additional information along with their name, like either the area, if they live in different area or their mother's or father's name, etc. Same situation can arise in your C++ applications. For example, you might be writing some code that has a function called xyz() and there is another library available which is also having same function xyz(). Now the compiler has no way of knowing which version of xyz() function you are referring to within your code. A namespace is designed to overcome this difficulty and is used as additional information to differentiate similar functions, classes, variables etc. with the same name available in different libraries. Using namespace, you can define the context in which names are defined. In essence, a namespace defines a scope.
Defining a Namespace
A namespace definition begins with the keyword namespace followed by the namespace name as follows:
namespace namespace_name { // code declarations }
To call the namespace-enabled version of either function or variable, prepend (::) the namespace name as follows:
name::code; // code could be variable or function.
Using Directive
You can also avoid prepending of namespaces with the using namespace directive. This directive tells the compiler that the subsequent code is making use of names in the specified namespace.
Discontiguous Namespaces
A namespace can be defined in several parts and so a namespace is made up of the sum of its separately defined parts. The separate parts of a namespace can be spread over multiple files. So, if one part of the namespace requires a name defined in another file, that name must still be declared. Writing a following namespace definition either defines a new namespace or adds new elements to an existing one:
namespace namespace_name { // code declarations }
Nested Namespaces
Namespaces can be nested where you can define one namespace inside another name space as follows:
namespace namespace_name1 { // code declarations namespace namespace_name2 { // code declarations } }
• Namespace is a feature added in C++ and not present in C. • A namespace is a declarative region that provides a scope to the identifiers (names of the types, function, variables etc) inside it. • Multiple namespace blocks with the same name are allowed. All declarations within those blocks are declared in the named scope. • Namespace declarations appear only at global scope. • Namespace declarations can be nested within another namespace. • Namespace declarations don't have access specifiers. (Public or private) • No need to give semicolon after the closing brace of definition of namespace. • We can split the definition of namespace over several units.
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/* namespaces in C++ language */ // A C++ code to demonstrate that we can define // methods outside namespace. #include <iostream> using namespace std; // Creating a namespace namespace ns { void display(); class happy { public: void display(); }; } // Defining methods of namespace void ns::happy::display() { cout << "ns::happy::display()\n"; } void ns::display() { cout << "ns::display()\n"; } // Driver code int main() { ns::happy obj; ns::display(); obj.display(); 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; }
#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; }


Randomly select pivot value from the subpart of the array. Partition that subpart so that the values left of the 'pivot' are smaller and to the right are greater from the pivot. And consider
In C++ language, The mode is the maximum of the "count of occurrence" of the different data element. This algorithm is beneficial for large dataset with high repetition frequency