# C++ Algorithm Library - generate_n() Function

## Description

The C++ function std::algorithm::generate_n() assigns the value returned by successive calls to gen to the first n elements of the sequence pointed by the first.

## Declaration

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

### C++11

```template <class OutputIterator, class Size, class Generator>
OutputIterator generate_n (OutputIterator first, Size n, Generator gen);
```

## Parameters

• first − Output iterator to the initial position.

• n − Number of values to generate.

• gen − Generator function that is called with no arguments and returns some value.

## Return value

Returns an an iterator which points to the element that follows the last element whose value has been generated.

## Exceptions

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

Please note that invalid parameters cause undefined behavior.

Linear.

## Example

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

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

using namespace std;

int main(void) {
int arr = {0, 0, 0, 0, 0, -100};

/* assign value to only first 5 elements */
auto it = generate_n(arr, 5, rand);

cout << "First five random numbers are" << endl;

for (int i = 0; i < 10; ++i)
cout << arr[i] << endl;

cout << endl;

cout << "Iterator points to " << *it << endl;

return 0;
}
```

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

```First five random numbers are
1804289383
846930886
1681692777
1714636915
1957747793
-100
0
0
0
0
Iterator points to -100
```
algorithm.htm