#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <math.h>
#include <string.h>

void itob(int n, char *s, unsigned b);

/* passes args to itob, n defaults to INT_MIN, base defaults to 10 */
int main(int argc, char *argv[])
{
    int n, b;
    n = (argc > 1) ? atoi(argv[1]) : INT_MIN;
    b = (argc > 2) ? atoi(argv[2]) : 10;
    if (b <= 0) {
        printf("error : invalid base %d\n", b);
        return 1;
    }

    char s[(int)log10(INT_MAX) + 3]; /* +3 for sign and \0 */
    itob(n, s, b);
    printf("%s\n", s);
    return 0;
}

void reverse(char *s);

/* itob: converts int n to string in base b and writes it to s */
void itob(int n, char *s, unsigned b)
{
    unsigned un;
    if (n < 0) {
        un = -n;
        *(s++) = '-';
    } else
        un = n;

    char d, *sc = s;
    do {
        d = un % b;
        *(sc++) = d + ((d > 9) ? 'a' - 10 : '0');
    } while ((un /= b) > 0);
    *sc = '\0';
    reverse(s);
}

/* reverse: reverses string s in place */
void reverse(char *s)
{
    char c, *s2;
    for (s2 = s + strlen(s) - 1; s < s2; s++, s2--)
        c = *s, *s = *s2, *s2 = c;
}