Memset is used to fill first n bytes in the block of memory pointed by a pointer to a specific character interpreted as an unsigned char. Memset is defined under string.h header.

Function Prototype

void * memset ( void * ptr, int value, size_t num );

About the parameters
ptr
ptr is the pointer to the block of memory
value
the value to be filled
num
number of bytes to be filled

Sample program using memset

#include <stdio.h>
#include <string.h>

int main()
{
        char c[] = "Findnerd";

        printf("Before applying memset : %s\n",c);

        memset(c,'+',4);

        printf("After applying memset  : %s\n",c);
        return 0;
}

Output of the above program

Before applying memset : Findnerd
After applying memset  : ++++nerd

In case you declare an integer array of size n with name arr and you want to fill all the locations with 0, then you can use memset instead of writing a separate code to set all the locations to 0. Use the following syntax for this purpose.
                          memset(arr,0,sizeof(arr));

This will set all memory locations in integer array arr to 0.