# std::count() in C++ STL

std::count() returns the number of occurrences of an element in a given range. Returns the number of elements in the range [first, last) that compare equal to val.

If the val is not found at any occurrence then it returns 0(Integer value).

// Returns count of occurrences of value in // range [begin, end] int count(Iterator first, Iterator last, T &val) first, last : Input iterators to the initial and final positions of the sequence of elements. val : Value to match

Complexity It’s order of complexity O(n). Compares once each element with a particular value. Counting occurrences in an array.

## CPP

 `// C++ program for count in C++ STL for` `// array` `#include ` `using` `namespace` `std;`   `int` `main()` `{` `    ``int` `arr[] = { 3, 2, 1, 3, 3, 5, 3 };` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]);` `    ``cout <<`   `        ``"  Number of times 3 appears : "` `    ``<< count(arr, arr + n, 3);`   `    ``return` `0;` `}`

Output

`  Number of times 3 appears : 4`

Time complexity: O(n)

Here n is size of array.

Auxiliary Space: O(1)

As constant extra space is used.

Counting occurrences in a vector.

## CPP

 `// C++ program for count in C++ STL for` `// a vector` `#include ` `using` `namespace` `std;`   `int` `main()` `{` `    ``vector<``int``> vect{ 3, 2, 1, 3, 3, 5, 3 };` `    ``cout << ``"Number of times 3 appears : "` `         ``<< count(vect.begin(), vect.end(), 3);`   `    ``return` `0;` `}`

Output

`Number of times 3 appears : 4`

Time complexity: O(n)

Here n is size of vector.

Auxiliary Space: O(1)

As constant extra space is used.

Counting occurrences in a string.

## CPP

 `// C++ program for the count in C++ STL` `// for a string` `#include ` `using` `namespace` `std;`   `int` `main()` `{` `    ``string str = ``"geeksforgeeks"``;`   `    ``cout << ``"Number of times 'e' appears : "` `         ``<< count(str.begin(), str.end(), ``'e'``);`   `    ``return` `0;` `}`

Output

`Number of times 'e' appears : 4`

Time complexity: O(n)

Here n is the length of string.

Auxiliary Space: O(1)

As constant extra space is used.

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