Tests whether a number is divisible by 11 and 9 or not

/*
Write a program to tests whether a number is divisible by 11 and 9 or not.
*/

#include<stdio.h>

int divisibleBy9(long int x);
int divisibleBy11(long int x);

main( )
{
 long int num;
 printf("Enter the number to be tested : ");
 scanf("%ld", &num);

 if(divisibleBy9(num))
 printf("The number is divisible by 9\n");

 else
 printf("The number is not divisible by 9\n");

 if(divisibleBy11(num))
 printf("The number is divisible by 11\n");

 else
 printf("The number is not divisible by 11\n");
}

/*divisibleBy9*/

int divisibleBy9( long int n )
{
 int sumofDigits;

 if(n==9)
 return 1;

 if(n<9)
 return 0;
 sumofDigits=0;

 while(n>0)
 {
  sumofDigits += n%10;
  n/=10;
 }
 divisibleBy9(sumofDigits);
}

/*divisibleBy11*/ 
int divisibleBy11( long int n )
{
 int s1=0, s2=0,diff;

 if(n == 0)
 return 1;

 if(n < 10)
 return 0;

 while(n>0)
 {
 s1 += n%10;
 n /=10;
 s2 += n%10;
 n /= 10;

 }
 diff = s1>s2 ? (s1-s2) : (s2-s1);
 divisibleBy11(diff);
}