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Vectors in C++ Programming Language

Vectors in C++ Language

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.

Declaration for Vectors in C++

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.

Initialization for Vectors in C++

// Vector initialization method 1 // Initializer list vector<int> vector1 = {1, 2, 3, 4, 5};

We are initializing the vector by providing values directly to the vector. vector1 is initialized with values 1, 2, 3, 4, 5.

// Vector initialization method 2 vector<int> vector3(5, 12);

Here, 5 is the size of the vector and 8 is the value. This code creates an int vector with size 5 and initializes the vector with the value of 8. So, the vector is equivalent to

vector<int> vector2 = {8, 8, 8, 8, 8};

The vector class provides various methods to perform different operations on vectors. Add Elements to a Vector: To add a single element into a vector, we use the push_back() function. It inserts an element into the end of the vector. Access Elements of a Vector: In C++, we use the index number to access the vector elements. Here, we use the at() function to access the element from the specified index. Change Vector Element: We can change an element of the vector using the same at() function. Delete Elements from C++ Vectors: To delete a single element from a vector, we use the pop_back() function. In C++, the vector header file provides various functions that can be used to perform different operations on a vector. • size(): returns the number of elements present in the vector. • clear(): removes all the elements of the vector. • front(): returns the first element of the vector. • back(): returns the last element of the vector. • empty(): returns 1 (true) if the vector is empty. • capacity(): check the overall size of a vector. Vector iterators are used to point to the memory address of a vector element. In some ways, they act like pointers.

Syntax for Vector Iterators in C++

vector<T>::iterator iteratorName;

We can initialize vector iterators using the begin() and end() functions. The begin() function returns an iterator that points to the first element of the vector. The end() function points to the theoretical element that comes after the final element of the vector.

/* Vectors in C++ language */ // C++ program to illustrate the capacity function in vector #include <iostream> #include <vector> using namespace std; int main() { vector<int> myvector; for (int i = 1; i <= 5; i++) myvector.push_back(i); cout << "Size : " << myvector.size(); cout << "\nCapacity : " << myvector.capacity(); cout << "\nMax_Size : " << myvector.max_size(); // resizes the vector size to 4 myvector.resize(4); // prints the vector size after resize() cout << "\nSize : " << myvector.size(); // checks if the vector is empty or not if (myvector.empty() == false) cout << "\nVector is not empty"; else cout << "\nVector is empty"; // Shrinks the vector myvector.shrink_to_fit(); cout << "\nVector elements are: "; for (auto it = myvector.begin(); it != myvector.end(); it++) cout << *it << " "; return 0; }

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Print all combination of a given length from the given array. Return if the currLen is more than the "required length". If currLen is equal to required length then "Print the sequence".

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