Binary number output in C

Question

I have an assignment to write a program that converts decimal numbers to binary numbers, in the C programming language.

This is the code I wrote:

#include <stdio.h>
#define MAX_LEN 1000

void translate_dec_bin(char s[]){
    unsigned int decNum;
    sscanf_s(s, "%d", &decNum);

    while (decNum > 0){
        printf("%d", decNum % 2);
        decNum = decNum / 2;
    }
    printf("\n");
}

main(){
    char s[MAX_LEN];
    char c='\0';
    int count=0;
    printf("enter a nunber\n");
    while (c < MAX_LEN && ((c = getchar()) != EOF) && c != '\n'){
        s[count] = c;
        ++count;
    }
    translate_dec_bin(s);
}

However, when the input is 1, the output I get is 1 instead of 0001. In other words, I want the 0's to appear in my output. How can I do that?

Use the debugger. Walk through your code a line at a time, inspecting variables as you go. You will soon see that your code is a bit of a mess and while someone will probably post an answer for you in order to gain the rep, you will not learn from that. You will learn from debugging this problem on your own. — mah
– mah, Commented Nov 8, 2013 at 21:15
Ok, thank you. I will try to find a guide to debug in Visual Studio. So you're saying there's a problem with my code that prevents from the zeros to be printed? @mah — Assaf
– Assaf, Commented Nov 8, 2013 at 21:18
I'm saying there's no reason to think the code you've provided would print these leading zeros and when you've stepped through, I suspect you will see the reason why. The problem is nothing particularly confusing and when you see it, you'll probably regret asking for help with it ;) — mah
– mah, Commented Nov 8, 2013 at 21:20
After that's cleaned up, you just need to decide how wide do you want the output to be… and add in code to ensure that it is. Once you get to that point, you're going to find that your bits are output in reverse order! so you'll need to figure out what to do about it (think: don't print right away… compute in reverse order as you already are and then print in the correct order -- though it's entirely possible to print in the correct order and deal with the leading 0's at the same time). — mah
– mah, Commented Nov 8, 2013 at 21:29
You're quite welcome. May I suggest your deleting this posted question as it's pretty unlikely to help others in the future? — mah
– mah, Commented Nov 8, 2013 at 21:32

Darth Hunterix · Accepted Answer · 2013-11-08 21:35:56Z

1

First, read mah's comment: although he suggest hitting a fly with a nuclear missile, he suggest you a right approach.

But in this case, your problem is simple: your loop in translate_dec_bin function finishes, because it has nothing left to do.

Think about for a second: your condition is "while decNum is greater than 0, print 1 or 0", right? I guess you know by now, that in C if you divide integer, the remainder is ommited, so 1/2=0.

Now look at your code: when you give argument "1", the loop iterates only once, so you get only one character in the output.

If you want more characters, you need more conditions. I leave it to you to come up with them, I'm not THAT reputation-hungry as mah suggested :)

And by the way: there is no way you can fit 1000 digits long number in an unsigned int, and that's what you're trying to do.

answered Nov 8, 2013 at 21:35

Darth Hunterix

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2 Comments

mah Over a year ago

Worse than not being able to fit that many digits into his number, his sentinel on the 1000 char buffer is errantly a char value, not the count he presumably intended to use. I'm not sure what "nuclear missile" approach you mean, but if you mean because I'm suggesting he rewrite most of his code (I am, and I can see why you could call that a nuke), it's because in my view, more code makes it harder to see problems… something that's often unavoidable (the code must be there), but in this case, it's a lot of unnecessary code helping hide real flaws (and introduce more)

Darth Hunterix Over a year ago

I meant debugger and rewriting everything from start. Don't get me wrong, I totally agree with every word you've written. I just still remember how intimidating comments like yours sounded when I was a beginner, and in a small program for learning purposes like his I don't see the point of scaring him like this. When his programs will start to work, then it's time for being serious.

UmNyobe · Accepted Answer · 2013-11-08 21:32:08Z

0

Assuming you already have computed your decimal number the basic idea without using print formating is the following:

char* list[] = {"0000", "000", "00", "0", ""};

char* leading_of(int num) {
   int v = 0;
   while(num > 0 && v < 4){
      num = num /10;
      v++;
   }
   return list[v];
}

printf("%s%d", leading_of(decNum), decNum);

If the number of characters or the padding character is variable you need to drop the list and do something more clever instead.

answered Nov 8, 2013 at 21:32

UmNyobe

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