Writing my own itoa function from scratch with no stdlib

Question

I am completely new to coding and have got this solution to another post working. I was wondering if there was a way to get it to work with negative integers as an input. I don't have access to the c standard libraries, hence my attempt to reproduce this post.

https://stackoverflow.com/a/31352708/18586829

Answer 1

Just check if the number is negative and prefix the - symbol:

#include <stdio.h>

char* int2basestr (int num, char* str, int radix) {
// extend the base as necessary
    char base[] = "0123456789ABCDEFGH"; // IJKLMN ....
    if (radix < 2 || radix > (sizeof(base) -1)) {  // radix supported?
        printf ("\nRadix/Base[%d] not yet supported, extend it\n", radix);
        str[0] = '\0';
        return str;
    }

    int si = 0;
    if (num < 0) {
        str[si++] = '-';
        num = -num;
    }
    char tmp[256];
    int rdi = -1;
    while (num) {
        tmp[++rdi] = base[num % radix];
        num /= radix;
    }
    while (rdi >= 0)
        str[si++] = tmp[rdi--];
    str[si] = '\0';
    return str;
}

#define TEST_COUNT  7

int main () {
    int values [TEST_COUNT] = { 12, -342, 332, -232, 675, +880, 34423 };
    int bases [TEST_COUNT] = {2, 3, 4, 5, 6, 16, 25};

    char strnum[256];

    for (int ti = 0; ti < TEST_COUNT; ++ti) {
        printf ("Num[%d] in Base[%d] is : [%s]\n", values[ti], bases[ti],
                int2basestr (values[ti], strnum, bases[ti]));
    }

    return 0;
}