C_PRG_LANG_EX_3.5

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

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

void reverse(char *s)
{
    int j = 0;
    while (s[j])
        j++;

    j--;
    for(int i = 0; j > i; j--, i++)
    {
        char tmp = s[i];
        s[i] = s[j];
        s[j] = tmp;
    }

    return;
}

void itob(int n, char *s, int base)
{
    int sign = 0;
    if (n < 0)
        sign++;

    char *start = s;

    do
    {
        int curr_numb = n % base;
        curr_numb = ABS(curr_numb);
        switch (curr_numb)
        {
        case 10:
            *s++ = 'A';
            break;
        case 11:
            *s++ = 'B';
            break;
        case 12:
            *s++ = 'C';
            break;
        case 13:
            *s++ = 'D';
            break;
        case 14:
            *s++ = 'E';
            break;
        case 15:
            *s++ = 'F';
            break;
        default:
            *s = curr_numb + '0';
            s++;
            break;
        }

        n /= base;
    } while (n);

    if (sign)
        *s++ = '-';

    *s = '\0';

    reverse(start);


}

int main(void)
{
    int numb = 1369;
    char string[256];

    for (int base = 2; base <= 16; base++)
    {
        printf("\n\n\nBASE IS %i\n", base);
        itob(numb, string, base);
        printf("%i\n%s\n\n", numb, string);

        numb = 1;
        itob(numb, string, base);
        printf("%i\n%s\n\n", numb, string);

        numb = -1;
        itob(numb, string, base);
        printf("%i\n%s\n\n", numb, string);

        numb = -0;
        itob(numb, string, base);
        printf("%i\n%s\n\n", numb, string);

        numb = INT_MAX;
        itob(numb, string, base);
        printf("%i\n%s\n\n", numb, string);

        numb = INT_MIN;
        itob(numb, string, base);
        printf("%i\n%s\n\n", numb, string);
    }

    return 0;
}