# fill() and fill_n() functions in C++ STL

• Difficulty Level : Basic
• Last Updated : 03 Jun, 2022

A vector, once declared, has all its values initialized to zero. Following is an example code to demonstrate the same.

## CPP

 `// C++ program for displaying the default initialization` `// of the vector vect[]` `#include` `using` `namespace` `std;`   `int` `main() ` `{` `    ``// Creating a vector of size 8` `    ``vector<``int``> vect(8);  `   `    ``// Printing default values` `    ``for` `(``int` `i=0; i

Output :

`0 0 0 0 0 0 0 0`

What if we wish to initialize the vector to a specific value, say 1 ? For this, we can pass the value along with the size of the vector.

## CPP

 `// C++ program for displaying specified initialization` `// of the vector vect[]` `#include` `using` `namespace` `std;`   `int` `main () ` `{` `    ``// Creates a vector of size 8 with all initial` `    ``// values as 1.` `    ``vector<``int``> vect(8, 1);  `   `    ``for` `(``int` `i=0; i

Output :

`1 1 1 1 1 1 1 1`

What if we wish to initialize the first 4 values to say 100 and rest 6 values as 200 ? One way to do this is to manually provide a value to each position in the vector. The other methods as provided in STL, the Standard Template Library, are fill and fill_n.

• fill() The ‘fill’ function assigns the value ‘val’ to all the elements in the range [begin, end), where ‘begin’ is the initial position and ‘end’ is the last position. NOTE : Notice carefully that ‘begin’ is included in the range but ‘end’ is NOT included. Below is an example to demonstrate ‘fill’ :

## CPP

 `// C++ program to demonstrate working of fill()` `#include ` `using` `namespace` `std;`   `int` `main ()` `{` `  ``vector<``int``> vect(8);`   `  ``// calling fill to initialize values in the` `  ``// range to 4` `  ``fill(vect.begin() + 2, vect.end() - 1, 4);`   `  ``for` `(``int` `i=0; i

• Output :
`0 0 4 4 4 4 4 0`
• fill_n() In fill_n(), we specify beginning position, number of elements to be filled and values to be filled. The following code demonstrates the use of fill_n.

## CPP

 `// 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

• Output :
``` 7 7 7 7 0 0 0 0
7 7 7 4 4 4 0 0```