main.c

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

char *readline(char **buf);
char *bin_to_hex(char *num);

static int strip_leading_zeroes(char **ptr) {
    int result = 0;
    while ((*ptr)[0] == '0' && (*ptr)[1] != '\0') {
        (*ptr)++;
        result++;
    }
    return result;
}

static inline void test_case(char *num) {
    char *hex = bin_to_hex(num);
    if (!hex) {
        printf("Invalid input.\n");
        return;
    }
    int leading_zeroes = strip_leading_zeroes(&hex);
    printf("hex(0b%s) = 0x%s\n", num, hex);
    free(hex - leading_zeroes);
}

int main(int argc, char **argv) {
    char *buf = calloc(10000, 1);
    while (true) {
        printf("Enter a binary number to convert: ");
        char *line = readline(&buf);
        if (strlen(line) && strcmp(line, "exit") != 0) {
            test_case(line);
        }
        else {
            break;
        }
    }
}