Reverse a String using strrev

#include<stdio.h>
#include<conio.h>
#include<string.h>
void main()
{      char s1[20];
clrscr();
    printf("\n\n program to reverse string using strrev");
printf("\n Enter any string: ");
gets(s1);
strrev(s1);
printf("\nReverse of string : %s", s1);
getch();
}