Subtracting two numbers without using '-' operator

#include <stdio.h>

int add(int a,int b)

{

int x;

x=a^b;

while(a&b)

{

b=((a&b)<<1);

a=x;

x=a^b;

//b=(a^b);

}

return x;

}

int sub(int a, int b) // add a with b's 2's complement.

{

return (add(a, add(~b, 1)));

}

int main() {

int a, b, res;

a = 3, b = 1;

printf ("Enter two no\n");

scanf ("%d %d",&a,&b);

res = sub(a, b);

printf("%d\n", res);

printf ("After Sub. is  no  %d",res);

return 0;

} 

output: 

Enter two no

10

5

After Sub. no is 5