Program in C to find the length of any string

Write a program in C to find the length of any string

#include<stdio.h>

#include<conio.h>

#include<math.h>

void main ()

{

          char ch [20];

          int l;

          clrscr ();

          printf ("Enter String: ");

          gets (ch);

          l=strlen(ch);

          printf ("Length of string is %d",l);

          getch ();

}