C++ Programming Code Examples

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. • 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.

copy() function is used to copy items from one iterator to another iterator with a specific range. We can define the start and end position of the source and it will copy all items in this rage to a different destination. To use copy() function, we need to include <bits/stdc+.h> or header file. It copies all the elements pointed by first and last. first element is included in the output but last is not. output is the start position of the final result iterator. It returns one iterator to the end of the destination range where elements have been copied. It is an input iterator to the first element of the range, where the element itself is included in the range. It is an input iterator to the last element of the range, where the element itself is not included in the range. Input iterators to the initial and final positions in a sequence to be copied. The range used 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. It is an output iterator to the first element of the new container in which the elements are copied. Output iterator to the initial position in the destination sequence. This shall not point to any element in the range [first,last). Function returns an iterator to the end of the destination range where elements have been copied. Linear in the distance between first and last: Performs an assignment operation for each element in the range. The objects in the range [first,last) are accessed (each object is accessed exactly once). The objects in the range between result and the returned value are modified (each object is modified exactly once). Throws if either an element assignment or an operation on iterators throws. Note that invalid arguments cause undefined behavior.

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. 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. Constant No changes 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. No-throw guarantee: this member function never throws exceptions. The copy construction or assignment of the returned iterator is also guaranteed to never throw.

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. 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 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.

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. A namespace definition begins with the keyword namespace followed by the namespace name as follows: To call the namespace-enabled version of either function or variable, prepend (::) the namespace name as follows: 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. 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: Namespaces can be nested where you can define one namespace inside another name space as follows: • 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.

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. Type of the elements. Aliased as member type deque::value_type. 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. • 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 • 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.

#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. 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. 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.

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. 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. Constant No changes The container is accessed. No contained elements are accessed: concurrently accessing or modifying them is safe. No-throw guarantee: this member function never throws exceptions.

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. 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). Constant No changes 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. 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).

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. 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). Constant 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. The container is modified. No existing elements are accessed (although see iterator validity above). 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.

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. initializes variables and is executed only once. if true, the body of for loop is executed, if false, the for loop is terminated. 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.

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). 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. Constant No changes 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. No-throw guarantee: this member function never throws exceptions. The copy construction or assignment of the returned iterator is also guaranteed to never throw.

Get string length. Returns the length of the C string str. C++ strlen() is an inbuilt function that is used to calculate the length of the string. It is a beneficial method to find the length of the string. The strlen() function is defined under the string.h header file. The strlen() takes a null-terminated byte string str as its argument and returns its length. The length does not include a null character. If there is no null character in the string, the behavior of the function is undefined. a string passed to this function, whose length needs to be found. Here str is the string variable of whose we have to find the length. It takes one parameter which is a pointer that points to the null-terminated byte string. The string is terminated by a null character. If a null character does not terminate it, then the behavior is undefined. It returns an integer giving the length of the passed string. Function returns the length of string. While calculating the total length of a String, the character at the first index is counted as 1 and not 0, i.e. one-based index . The function strlen returns the total number of characters actually present in the char[] and not the total number of character it can hold.

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. 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). Constant No changes. 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. No-throw guarantee: this member function never throws exceptions. The copy construction or assignment of the returned iterator is also guaranteed to never throw.

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. 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). Constant No changes 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. No-throw guarantee: this member function never throws exceptions. The copy construction or assignment of the returned iterator is also guaranteed to never throw.