Table Addition

/* PREPROCESSOR DIRECTIVES */
#include <stdio.h>

/* FUNCTION PROTOTYPES */
int add(int, int, int);

/* MAIN ENTRY POINT */
int main(void)
{
     int num1, num2;

      printf("Enter two positive integers: ");
      scanf("%d %d", &num1, &num2);
      printf("Sum = %d\n", add(num1, num2, 1));

      return 0;
}

/* FUNCTION DEFINITIONS */

/*
* <summary> Recursively performs addition on 2 integers </summary>
* <params>
*   "n1", "n2" = The two integers to perform addition on
*   "carry" = The weight of the last digit of both numbers
* </params>
* <return> Computed addition of "n1" and "n2" </return>
* <precond> Both "n1" and "n2" should contain the same number of digits and do not have leading zeroes </precond>
*/
int add(int n1, int n2, int carry)
{
     int sum;

     //Both are equal in length, so if n1 <=0, n2 as well
      if (n1 > 0)
     {
          //Add last digits and multiply with their weight
         sum = (n1%10 + n2%10) * carry;

    //Recursion - Remove last digit and increase weight by a factor of 10
         return sum + add(n1/10, n2/10, carry*10);
      }
      else
           return 0;

}