Print an int in C without Printf or any functions

Question

I have an assignment where I need to print an integer in C without using printf, putchar, etc. No header files allowed to be included. No function calls except for anything I wrote. I have one function my_char I am using (maybe its wrong) but it prints out a character. I currently have the following code which is printing the number out backwards. Not looking for an answer. Just looking for some direction, some help, maybe I'm looking at it completely wrong.

void my_int(int num)
{   
  unsigned int i;    
  unsigned int j;

  char c;

  if (num < 0)    
    {
      my_char('-');
      num = -num;
    }

  do    
    {
      j = num % 10;
      c = j + '0';
      my_char(c);
      num = num/10;
    }while(num >0);
}

Answer 1

Instead of calling my_char() in the loop instead "print" the chars to a buffer and then loop through the buffer in reverse to print it out.

Turns out you can't use arrays. In which case you can figure out the max power of 10 (ie log10) with the loop. Then use this to work backwards from the first digit.

unsigned int findMaxPowOf10(unsigned int num) {
    unsigned int rval = 1;
    while(num) {
        rval *= 10;
        num /= 10;
    }
    return rval;
}

unsigned int pow10 = findMaxPowOf10(num);

while(pow10) {
    unsigned int digit = num / pow10;
    my_char(digit + '0');
    num -= digit * pow10;
    pow10 /= 10;
}