# C++ Algorithm Library - count_if() Function

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## Description

The C++ function std::algorithm::count_if() returns the number of occurrences of value from range that satisfies condition.

## Declaration

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

### C++98

```template <class InputIterator, class Predicate>
typename iterator_traits<InputIterator>::difference_type
count_if (InputIterator first, InputIterator last, UnaryPredicate pred);
```

## Parameters

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

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

• pred − Unary predicate which takes an argument and returns bool.

## Return value

Returns the number of elements in the range for which pred returns true.

## Exceptions

Throws an exception if either predicate 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_if() function.

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

using namespace std;

bool predicate(int n) {
return (n > 3);
}

int main(void) {
vector<int> v = {1, 2, 3, 4, 5};
int cnt;

cnt = count_if(v.begin(), v.end(), predicate);

cout << "There are " << cnt << " numbers are greater that 3." << endl;

return 0;
}
```

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

```There are 2 numbers are greater that 3.
```
algorithm.htm