Why won't this C code run at the 'while' loop? - c

Question

So I'm working on this assignment. I tried running this code, and it ceases to work after reading in the second number. Here is a synopsis of it:
Write a C program that prompts the user to enter two positive integers. Your program should then display the number of carry operations that result from adding the two numbers and print the result of the addition. The input continues until the user enters 0 for the first number.
For instance, if the input is 123 and 456, there are 0 carry operations. If the input is 666 and 777, there are 3 carry operations.
Here's my code (nothing happens once it gets to the while loop):
#include <stdio.h>
#include <string.h>
// ------------------------
char dummy;
char response = 'y';
int userNum1, userNum2, sum;
int carry = 0;
int factor = 1;
int digit1 = 1;
int digit2 = 1;
int main(void)
{
while (response == 'y' || response == 'Y')
{
printf ("Enter the first number: ");
scanf ("%d", &userNum1);
printf ("Enter the second number: ");
scanf ("%c", &dummy);
scanf ("%d", &userNum2);
sum = userNum1 + userNum2;
while (userNum1 > 0 && userNum2 > 0)
{
while (digit1 > 0 && digit2 > 0)
{
digit1 = getNum (userNum1);
digit2 = getNum (userNum2);
factor = factor * 10;
carryTheOne (digit1, digit2);
}
}
printf ("The sum is %d and there were %d carry operations", sum, carry);
printf("\n");
printf ("Do you want to do another one?");
scanf ("%c", &dummy);
scanf ("%c", &response);
scanf ("%c", &dummy);
}
return 0;
}
int getNum(int num)
{
num = ((num % (factor * 10)) / factor);
return num;
}
int carryTheOne (int num1, int num2)
{
if ((digit1 + digit2) > 9)
carry++;
return carry;
}
Can someone help me here and let me know what I'm doing wrong? It just prints a blank line after reading the second number and never does anything else (doesn't terminate, just doesn't do anything).
EDIT: I changed the while loop to this:
while (userNum1 > 0 && userNum2 > 0)
{
while (digit1 > 0 && digit2 > 0)
{
digit1 = getNum (userNum1);
digit2 = getNum (userNum2);
factor = factor * 10;
carryTheOne (digit1, digit2);
userNum1 = (userNum1 - digit1) / 10;
userNum2 = (userNum2 - digit2) / 10;
}
}
It worked for 123 and 456, but didn't work for 666 and 777. Any reason why?

Answer 1

Remove that factor variable. I have made for edits:
1.Comment out
int factor = 1;
2.comment out
factor = factor * 10;
3.change
userNum1 = (userNum1 - digit1) / 10;
userNum2 = (userNum2 - digit2) / 10;
to
userNum1 = userNum1 / 10;
userNum2 = userNum2 / 10;
4.change:
int getNum(int num)
{
num = ((num % (factor * 10)) / factor);
return num;
}
to
int getNum(int num)
{
num = num % 10;
return num;
}