C++ Vectors

• In C++, vectors are used to store elements of similar data types. However, unlike arrays, the size of a vector can grow dynamically. That is, we can change the size of the vector during the execution of a program as per our requirements.
• Vectors are part of the C++ Standard Template Library. To use vectors, we need to include the vector header file in our program.

Vector Declaration :-

std::vector<T> vector_name;        

The type parameter <T> specifies the type of the vector. It can be any primitive data type such as int, char, float, etc.

vector<int> num;        

Here, num is the name of the vector. we have not specified the size of the vector during the declaration. This is because the size of a vector can grow dynamically so it is not necessary to define it.

Member Functions of Vectors in C++

A Vector container in STL provides us with various useful functions.

1. Modifiers
2. Iterators
3. Capacity

Modifiers

1. push_back(): The function pushes the elements into a vector from the back. If the type of object passed as a parameter in the push_back() is not same as that of the vector an exception is thrown.
2. assign(): It assigns a new value to the vector elements by replacing old ones.
3. pop_back(): The pop_back() function is used to pop or remove elements from a vector from the back. It reduces the size of the vector by one element.
4. insert(): This function inserts new elements before the element before the position pointed by the iterator. We can also pass a third argument count, that counts the number of times the element is to be inserted before the pointed position.
5. erase(): erase() function is used to remove elements from a container from the sp
6. swap(): swap() function is used to swap the contents of one vector with another vector of the same type. Sizes may differ.
7. clear(): clear() function is used to remove all the elements of the vector container

Iterators

1. begin(): This function returns an iterator pointing to the first element in the vector.
2. end(): The end() function returns an iterator pointing to the last element in the vector.

Capacity

1. size(): This function returns the number of elements in the vector.
2. max_size(): The max_size() function returns the maximum number of elements that the vector can hold.
3. capacity(): The capacity() function returns the size of the storage space currently allocated to the vector expressed as number of elements based on the memory allocated to the vector.
4. resize(): This function resizes the container so that it contains ‘n’ elements. If the current size of the vector is greater than n then the back elements are removed from the vector and id the current size is smaller than n then extra elements are inserted at the back of the vector.
5. empty(): Returns whether the container is empty, it return true if vector is empty else returns false.

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