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


// returns the number of digits needed to write number n.
// if the number is negative, the minus sign is NOT counted
// as one of the digits.
int count_digits(int n)
{
  int result = 1;
  int temporary = n;

  if (n < 0)
  {
    temporary = -n;
  }

  while(1)
  {
    if (temporary < 10)
    {
      break;
    }

    temporary = temporary / 10;
    result++;
  }

  return result;
}


// if n has fewer digits than result_digits,
// we add as many zeros to the right of n as needed
// to make it have length result_digits. If n
// already has result_digits or more digits, we 
// do not add any zeros.
char * pad_number(int n, int result_digits)
{
  int digits = count_digits(n);
  int number_of_zeros = 5 - digits;
  int result_length;

  if (number_of_zeros < 0)
  {
    number_of_zeros = 0;
    result_length = digits;
  }
  else
  {
    result_length = 5;
  }

  char * result = (char *) malloc(sizeof(char) * result_length + 1);
  int i;
  for (i = 0; i < number_of_zeros; i++)
  {
    result[i] = '0';
  }

  int temporary = n;
  for (i = 0; i < digits; i++)
  {
    result[result_length - i - 1] = (temporary % 10) + 48;
    temporary = temporary / 10;
  }

  result[result_length] = 0;
  return result;
}


int main()
{
  int number;
  printf("enter a number\n");
  scanf("%d", &number);

  if (number < 0)
  {
    printf("cannot handle negative numbers, exiting...\n");
    return 0;
  }  

  int digits = count_digits(number);
  printf("%d contains %d digits\n", number, digits);

  char * result = pad_number(number, 5);
  printf("result = %s\n", result);

  free(result);
}