Tuesday, July 15, 2008

Converting Binary Numbers To Decimal The Hard Way On Linux Or Unix

Hey There,

If you recall a while back, we looked at using Perl's "unpack" function to easily convert binary values to decimal and convert decimal back to binary. Those were both (some folks may consider) relatively sophisticated methods of tackling the problem. Although, once you understand how "unpack" works, the first becomes incredibly simple to use and understand. The other one may always be a little awkward.

Today we're going to look at doing binary to decimal conversion using a less "worldly" method ;) The program we have for you today (and I refer to it as a program since it's written in C) attacks the problem more naturally. And, by naturally, I mean that it should make sense to anyone at its core (assuming they understand the C programming language). The method of execution is not the most efficient, but I think it's the most "human readable." In a future post, we'll definitely convert it to Perl, shell and Awk. And, maybe before then, we'll get to the next part in our ongoing series on Perl, shell and Awk porting. We'll get there eventually. If I didn't have so many different things to write about, I could bore you to tears with that stuff (if I haven't already ;)

Hope you enjoy the program. You can build it easily, using a compiler like gcc in this fashion:

host # gcc -o bin2dec bin2dec.c

and run it just as easily:

host # $ ./bin2dec

8 Digit Binary Number?
<-- I think there's a subtle homage to Rush in there - just forget about the ending 0 ;)

Binary 10010010 equals Decimal 146!

The only catch, which the executable program will prompt you with, is that (in order to keep it simple) it's limited to 8 digit binary numbers and expects an 8 digit binary number as input. This means that binary 1 would return 128 (10000000) instead of 1 (00000001). Both symptoms can be fixed by adding extra code to pad zeros on the left hand side, but I felt, after seeing the resulting code, that including it would take away from the basic gist of this post, which is that C, Perl, shell and Awk are totally accessible to "anyone" who wants to learn them. I wanted to put something out that looked as little like a completely foreign language as possible. It is my philosophy that anyone can learn how to code and/or use the Linux or Unix Operating System(s).

Of course, if "everyone" loses their irrational "fear of computers" and does start doing this stuff well, I'll end up being a fry-guy at McDonald's in about 10 years ;)


Creative Commons License

This work is licensed under a
Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License

* bin2dec - Convert 8 digit binary numbers *
* to decimal numbers *
* *
* 2008 - Mike Golvach - eggi@comcast.net *
* *

/* Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License */

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


char binnumber[8];
int length;
int difference;
int total = 0;

printf("\n8 Digit Binary Number?\n");
scanf("%s", &binnumber);
length = strlen(binnumber);
if ( length < 8 ) {
difference = -(length - 8);
if ( binnumber[7] == '1' ) {
total = total + 1;
if ( binnumber[6] == '1' ) {
total = total + 2;
if ( binnumber[5] == '1' ) {
total = total + 4;
if ( binnumber[4] == '1' ) {
total = total + 8;
if ( binnumber[3] == '1' ) {
total = total + 16;
if ( binnumber[2] == '1' ) {
total = total + 32;
if ( binnumber[1] == '1' ) {
total = total + 64;
if ( binnumber[0] == '1' ) {
total = total + 128;
printf("\nBinary %s equals Decimal %d!\n", binnumber, total);
return 0;

, Mike