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# fill_n() function in C++ STL with examples

• Last Updated : 11 Oct, 2019

The fill_n() function in C++ STL is used to fill some default values in a container. The fill_n() function is used to fill values upto first n positions from a starting position. It accepts an iterator begin and the number of positions n as arguments and fills the first n position starting from the position pointed by begin with the given value.

Syntax:

```void fill_n(iterator begin, int n, type value);
```

Parameters:

• begin: The function will start filling values from the position pointed by the iterator begin.
• n: This parameter denotes the number of positions to be filled starting from the position pointed by first parameter begin.
• value: This parameter denotes the value to be filled by the function in the container.

Return Value: This function does not returns any value.

Below program illustrate the fill_n() function in C++ STL:

 `// C++ program to demonstrate working of fil_n()``#include ``using` `namespace` `std;`` ` `int` `main()``{``    ``vector<``int``> vect(8);`` ` `    ``// calling fill to initialize first four values``    ``// to 7``    ``fill_n(vect.begin(), 4, 7);`` ` `    ``for` `(``int` `i = 0; i < vect.size(); i++)``        ``cout << ``' '` `<< vect[i];``    ``cout << ``'\n'``;`` ` `    ``// calling fill to initialize 3 elements from``    ``// "begin()+3" with value 4``    ``fill_n(vect.begin() + 3, 3, 4);`` ` `    ``for` `(``int` `i = 0; i < vect.size(); i++)``        ``cout << ``' '` `<< vect[i];``    ``cout << ``'\n'``;`` ` `    ``return` `0;``}`
Output:
```7 7 7 7 0 0 0 0
7 7 7 4 4 4 0 0
```
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