C_PRG_LANG_EX_4.12

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

#define ABS(n) n >= 0 ? n : -n

void my_itoa(int numb, char *s);
void my_itoa_rec(int numb, char **s);

void my_itoa_rec(int numb, char **s)
{
    if (numb)
        my_itoa_rec(numb / 10, s);
    else
    {
        return;
    }

    int digit = numb % 10;
    digit = ABS(digit);
    **s = digit + '0';
    (*s)++;
    **s = '\0';

    return;
}

void my_itoa(int numb, char *s)
{
    if (!numb)
    {
        s[0] = '0';
        s[1] = '\0';
        return;
    }
    if (numb < 0)
        *s++ = '-';

    my_itoa_rec(numb, &s);
}

int main (void)
{
    int numb = INT_MAX;
    char s[256];

    my_itoa(numb, s);
    printf("%s\n", s);

    numb = INT_MIN;
    my_itoa(numb, s);
    printf("%s\n", s);

    numb = 0;
    my_itoa(numb, s);
    printf("%s\n", s);
    return 0;
}