All you need to do is change the type of the 'bin' parameter and, in fact, since you mentioned the possibility of an unsigned long version, the following is the only unsigned version that is necessary unless you're really concerned about speed. You see, with this version, an unsigned int value or unsigned char value can be used as the 'bin' parameter without needing special cases. One size fits all.

/****************************************************************************
 *
 *    NAME: UlToStr
 * PURPOSE: Convert unsigned long to decimal string.
 *
 * SYNOPSIS:   void UlToStr(char *s, unsigned long bin, unsigned char n);
 *
 * DESCRIPTION:
 *
 *     The function stores a NUL-terminated string, in "n" + 1 (plus 1 for
 *     the NUL string terminator) successive elements of the array whose
 *     first element has the address "s", by converting "bin" to "n" decimal
 *     characters.
 *
 ****************************************************************************/

void UlToStr(char *s, unsigned long bin, unsigned char n)
{
    s += n;
    *s = '';

    while (n--)
    {
        *--s = (bin % 10) + '0';
        bin /= 10;
    }
}