gistfile1.h

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/* Define a constant */
#define NUMBER 110771

int ctoi(char c)
{
    return (int)c - 48;
}

int main(int argc, char** argv)
{
    int res = NUMBER * 9;
    char as_string[11] = {0};
    int as_string_len = 0;
    int i = 0;

    printf("Multiply any number by 9 and add the numbers in the result.\nYou will get a 9.\n\n");
    printf("Number %d * 9 = %d\n", NUMBER, res);

    while(res > 9)
    {
        itoa(res, as_string, 10);
        as_string_len = strlen(as_string);

        res = 0;
        for(i = 0; i < as_string_len; i++)
        {
            res += ctoi(as_string[i]);

            if(i < as_string_len-1)
            {
                printf("%c+", as_string[i]);
            }
            else
            {
                printf("%c\n", as_string[i]);
            }
        }
        printf("Sum = %d\n", res);
    }

    return 0;
}