How to make my Hexadecimal spit out 8 digits(including leading zeros)

So, I wrote a function converting a decimal number into a hexadecimal number by using recursion, but I can't seem to figure out how to add the prefix "0x" and leading zeros to my converted hexadecimal number. Let's say I pass the number 18 into the parameters of my function. The equivalent hexadecimal number should be 0x00000012. However, I only end up getting 12 as my hexidecimal number. The same applies when I pass in a hexidecimal number 0xFEEDDAD. I end up getting only FEEDDAD without the prefix as my answer. Can someone please help me figure this out? I've listed my code below. Also, I'm only allowed to use fputc to display my output.

const char digits[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";

void hexout (unsigned long number, FILE * stream) 
{
     long quotient;
     long remainder;

     quotient = number / 16;
     remainder = number % 16;


     if(quotient != 0)
       hexout(quotient,stream);


     fputc(digits[remainder],stream);
}

void hexout (unsigned long number, FILE * stream) 
{
    fprintf(stream, "0x%08lX", number);
}

If you cannot use fprintf (neither sprintf), you can use this kind of code (no recursion, but a 8-chars array on the stack):

const char digits[] = "0123456789ABCDEF";

void hexout(unsigned long number, FILE * stream)
{
  unsigned long int input = number;
  unsigned long int quotient;
  unsigned long int remainder;
  unsigned short ndigit = 0;
  char result[8] = {0};

  // Compute digits
  do
  {
     quotient  = input / 16;
     remainder = input % 16;
     result[7-ndigit] = digits[remainder];
     input = quotient;
     ndigit++;
  }
  while (ndigit < 8);

  // Display result

  fputc('0', stream);
  fputc('x', stream);
  for (ndigit = 0; ndigit < 8; ndigit++)
  {
    fputc(result[ndigit], stream);
  }
}

Of course, this can be improved a lot...