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# fill_n

Replaces n elements with a given value

## Definition

The fill_n() algorithm is defined in the standard header <algorithm> and in the nonstandard backward-compatibility header <algo.h>.

## Interface

```#include <algorithm>
template < class OutputIterator, class Size, class Type >
void fill_n(
OutputIterator first,
Size count,
const Type& val
);```

Parameters:
Parameter Description
first An output iterator addressing the position of the first element in the range to be assigned the value `val`
count A signed or unsigned integer type specifying the number of elements to be assigned the value
val The value to be assigned to elements in the range `[first, first + count)`

## Description

Fill_n algorithm does the same thing that fill but fills `n` elements.

None.

## Complexity

The complexity is linear; performs `n` assignments.

### References

Example:
##### Example - fill_n function
Problem
The following program demonstrates how to use fill_n() function.
Workings
```#include <vector>
#include <algorithm>
#include <iostream>

using namespace std;

int main()
{
vector <int> vec;
vector <int>::iterator Iter1;
int i;
for (i = 10; i <= 20; i++)
vec.push_back(i);
cout <<"Vector vec data: ";
for (Iter1 = vec.begin(); Iter1 != vec.end(); Iter1++)
cout <<*Iter1<<" ";
cout <<endl;
// fill the last 3 positions for 6 position with a value of 9
cout <<"\nOperation: fill_n(vec.begin() + 3, 6, 9)\n";
fill_n(vec.begin() + 3, 6, 9);
cout <<"Modified vec data: ";
for (Iter1 = vec.begin(); Iter1 != vec.end(); Iter1++)
cout <<*Iter1<<" ";
cout <<endl;

return 0;
}```
Solution
Output:

Vector vec data: 10 11 12 13 14 15 16 17 18 19 20
Operation: fill_n(vec.begin() + 3, 6, 9)
Modified vec data: 10 11 12 9 9 9 9 9 9 19 20
References