basechange.c

/*
 * basechange.c
 * This is a simple tool to display a number (from any base) in decimal, hexadecimal, octal, and binary.
 */
#include <stdio.h>
#include <stdlib.h>

void print_all_bases(int n);
void print_bits(int n);

int main(int argc, char **argv) {
	int base = 0;
	
	// Read the number we got
	if (argc < 2) {
		printf("%s <number> [base]\n", argv[0]);
		return 1;
	}

	// Read the base we got, if we did
	if (argc >= 3) {
		base = atoi(argv[2]);
	}

	// Parse the number we got and print it in other bases
	// Note strtol can detect hex and octal, and accepts 0 as a base
	// (unspecified base). NULL lets it read the whole string.
	print_all_bases(strtol(argv[1], NULL, base));

	return 0;
}

void print_all_bases(int n) {
	printf("Dec:\t%d\nHex:\t0x%X\nOctal:\t0%o\n", n, n, n, n);
	printf("Binary:\t0b");
	print_bits(n);
	putchar('\n');
}

void print_bits(int n) {
	if (n > 0) {
		print_bits(n/2);
		putchar(n%2==0?'0':'1');
	}
}