C program to multiply two numbers using recursion

Write a C program to find the product of two numbers using recursion.

  #include <stdio.h>

  /* product of two number using recursion */
  void product(int *val1, int *val2, int temp, int sign) {
        if (*val2 <= 1) {
                printf("%d\n", ((*val1) * sign));
                return;
        }

        /* val2 time val1 is the product value */
        *val1 = *val1 + temp;
        *val2 = *val2 - 1;

        /* finding product using recursion */
        product(val1, val2, temp, sign);
        return;
  }

  int main() {
        int val1, val2, temp, sign = 1;

        /* get the first input from the user */
        printf("Enter your first input:");
        scanf("%d", &val1);

        /* get the second input from the user */
        printf("Enter your second input:");
        scanf("%d", &val2);

        /* if any one of the input is negative, output is also -ve */

        if ((val1 < 0 && val2 > 0) ||

                (val1 > 0 && val2 < 0)) {

                sign = -1;

        } else if (val1 == 0 || val2 == 0) {

                /* if any of the i/p is 0, the o/p is also 0 */

                printf("Product of %d and %d is 0\n", val1, val2);

                return 0;

        }

        printf("Product of %d and %d is ", val1, val2);

        /* finding the absolute values of both the inputs */

        val1 = abs(val1);

        val2 = abs(val2);

        temp = val1;

        /* find product of two numbers using recursion */

        product(&val1, &val2, temp, sign);

        return 0;

  }

  Output:

  jp@jp-VirtualBox:~/$ ./a.out
  Enter your first input:20
  Enter your second input:40
  Product of 20 and 40 is 800

  jp@jp-VirtualBox:~/$ ./a.out
  Enter your first input:0
  Enter your second input:40
  Product of 0 and 40 is 0

  jp@jp-VirtualBox:~/$ ./a.out
  Enter your first input:10
  Enter your second input:1
  Product of 10 and 1 is 10

  jp@jp-VirtualBox:~/$ ./a.out
  Enter your first input:10
  Enter your second input:-1
  Product of 10 and -1 is -10

  jp@jp-VirtualBox:~/$ ./a.out
  Enter your first input:-10
  Enter your second input:-1
  Product of -10 and -1 is 10