[06/4/13] Challenge #128 [Easy] Sum-the-Digits, Part II - http://www.reddit.com/r/dailyprogrammer/comments/1fnutb/06413_challenge_128_easy_sumthedigits_part_ii/

Sum-the-Digits-II.c

/*
(Easy): Sum-the-Digits, Part II (http://www.reddit.com/r/dailyprogrammer/comments/1fnutb/06413_challenge_128_easy_sumthedigits_part_ii/)
------------------------------------------------------------------------------------------------------------------------------------------

Given a well-formed (non-empty, fully valid) string of digits, let the integer N be the sum of digits. Then, given this integer N, turn it into a string of digits. Repeat this process until you only have one digit left. Simple, clean, and easy: focus on writing this as cleanly as possible in your preferred programming language.

`Author: nint22. This challenge is particularly easy, so don't worry about looking for crazy corner-cases or weird exceptions. This challenge is as up-front as it gets :-) Good luck, have fun!`

Formal Inputs & Outputs
-----------------------

### Input Description ###

On standard console input, you will be given a string of digits. This string will not be of zero-length and will be guaranteed well-formed (will always have digits, and nothing else, in the string).

### Output Description ###

You must take the given string, sum the digits, and then convert this sum to a string and print it out onto standard console. Then, you must repeat this process again and again until you only have one digit left.

Sample Inputs & Outputs
-----------------------

### Sample Input ###

Note: Take from Wikipedia for the sake of keeping things as simple and clear as possible.

12345

### Sample Output ###

12345
15
6
*/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>

void usage(char *argv0);
void sumOfDigits(unsigned long *sum, size_t *lenDigitsOut, char *digits);
void convertNumberToString(char **stringOut, unsigned long num);

int main(int argc, char *argv[])
{
    char *str = NULL;
    unsigned long sum = 0;
    size_t lenDigits = 0;

    if (argc != 2)
    {
        usage(argv[0]);
        exit(1);
    }

    sumOfDigits(&sum, &lenDigits, argv[1]);
    printf("str: %s lenDigits: %lu\n", argv[1], lenDigits);
    while(lenDigits > 1 )
    {
        convertNumberToString(&str, sum);
        sumOfDigits(&sum, &lenDigits, str);
        printf("str: %s lenDigits: %lu\n", str, lenDigits);
    }
}

/**
 * Print usage infomation in command line.
 * @param argv0 The name of the executable
 */
void usage(char *argv0)
{
    printf("Usage: %s [string of digits]\n", argv0);
    return;
}

/**
 * Calculate the sum of digits from a string.
 * @param digits The string which contains the digits
 * @param lenDigitOut Returns the length of the string
 * @param sumOut Returns the sum of the digits of the string
 */
void sumOfDigits(unsigned long *sumOut, size_t *lenDigitsOut, char *digits)
{
    *sumOut = 0;
    *lenDigitsOut = strlen(digits);
    size_t i = 0;

    for(i = 0;i<*lenDigitsOut;i++)
        if (isdigit(digits[i])) /** Check if character is digit. */
            *sumOut += (digits[i] - '0');
}

/**
 * Convert an unsigned long number to string
 * @param num The number to be converted to string
 * @param stringOut The converted string from the number
 */
void convertNumberToString(char **stringOut, unsigned long num)
{
   /** Free memory if already allocated. */
   if (*stringOut != NULL)
       free(*stringOut);

   size_t numLen = snprintf(NULL, 0, "%lu", num);
   if (numLen < 0)
       return;

   *stringOut = (char *)malloc(numLen+1);
   snprintf(*stringOut, numLen+1, "%lu", num);
}