checkDigit.c

//Can we write a program that adds up the digits of a number?

/*
$ ./checkDigit
Enter a number: 567
The digits of 567 add up to 18
*/

#include <stdio.h>
#include <cs50.h>

int main(void)
{

    int num = 0;
    int total = 0;
    int lastDigit = 0;

    num = get_int("Enter a number: ");

    //Save a copy of the number for use in the final message
    int numSaved = num;

    while (num > 0)
    {

        //use mod operator (%) to get the last digit
        //eg:  567 % 10 gives a 7, since 567 / 10 is 56 with remainder 7.
        lastDigit = num % 10;

        //Add the digit to the running total
        total = total + lastDigit;

        //Chop off the last digit, now that we're done with it
        //Divide by 10, but stored in an integer just drops the last digit
        //eg:  567 / 10 = 56.7 but as int its just stored as 56.   The 7 is now gone.
        num = num / 10;
    }
    printf("The digits of %i add up to %i\n", numSaved, total);
}