# C++ Algorithm Library - count() Function

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## Description

The C++ function std::algorithm::count() returns the number of occurrences of value in range. This function uses operator == for comparison.

## Declaration

Following is the declaration for std::algorithm::count() function form std::algorithm header.

### C++98

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

## Parameters

• first − Input iterators to the initial positions of the searched sequence.

• last − Input iterators to the final positions of the searched sequence.

• val − Value to search for in the range.

## Return value

Returns the number of elements in the range of first to last.

## Exceptions

Throws an exception if either element assignment or an operation on an iterator throws exception.

Please note that invalid parameters cause undefined behavior.

## Time complexity

Linear in the distance between first to last.

## Example

The following example shows the usage of std::algorithm::count() function.

```#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main(void) {
vector<int> v = {1, 3, 3, 3, 3};
int cnt;

cnt = count(v.begin(), v.end(), 3);

cout << "Number 3 occurs " << cnt << " times." << endl;

return 0;
}
```

Let us compile and run the above program, this will produce the following result −

```Number 3 occurs 4 times.
```
algorithm.htm