# C++ <algorithm> - count() Function

The C++ algorithm::count function returns the number of occurrences of specified value val in the range [first, last).

### Syntax

template <class InputIterator, class T>
typename iterator_traits<InputIterator>::difference_type
count (InputIterator first,
InputIterator last,
const T& val);

### Parameters

 first Specify initial position of the input iterator. The range used is [first,last). last Specify final position of the input iterator. The range used is [first,last). val Specify the value to be counted.

### Return Value

Returns number of occurrences of val in the range [first, last).

### Time Complexity

Linear i.e, Θ(n).

### Example:

In the example below, the algorithm::count function is used to find out the number of occurrences of specified value in the given vector.

#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

int main (){
vector<int> vec{10, 20, 30, 10, 10, 20, 50};

//find out the number of occurrences of 10
int retval1 = count(vec.begin(), vec.end(), 10);
cout<<"Number of occurrences of 10: "<<retval1<<endl;

//find out the number of occurrences of 20
int retval2 = count(vec.begin(), vec.end(), 20);
cout<<"Number of occurrences of 20: "<<retval2;

return 0;
}

The output of the above code will be:

Number of occurrences of 10: 3
Number of occurrences of 20: 2

❮ C++ <algorithm> Library

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