Decimal to Binary

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December 3rd, 2009, 06:40 PM

Neutralise

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Decimal to Binary

Im trying to make a program which converts a decimal to binary (without bitwise operators), however I am getting some strange output and can not see what Im doing wrong, any help?

http://codepad.org/ILZHyYb9

Thanks.

December 3rd, 2009, 06:50 PM

jwdonahue

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Post your code (use code tags). Post the output you are getting and tell us what you expected to get.

Read this:

http://forums.devshed.com/c-program...rst-259106.html

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December 3rd, 2009, 07:27 PM

Neutralise

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Sorry, I figured code pad would be easer.

Code:

#include <stdio.h>

char binaryConvert(int c);
char reverse(void);
int number = 12;
char binaryRep[4] = "0000";
char reverseRep[4] = "0000";

// convert decimal number into binary representation
int main(){
  binaryConvert(number);
  reverse();
  printf("%d in binary: %s \n", number, binaryRep);
  return 0;
}

// convert decimal into binary
char binaryConvert(int c){
  int i = 0;
  int tempNumber = number;
  int remain = 0;
  while(tempNumber > 0){
  remain = tempNumber % 2;
  tempNumber = tempNumber / 2;
  //  printf("%d/2 = %d remainder = %d \n", tempNumber * 2, tempNumber, remain);
  reverseRep[i] = remain + '0';
  i++;
  }
  return 1;
}

// reverse binary number
char reverse(void){
  int start = 0;
  int end = 3;
  while (end >= 0){
    binaryRep[start] = reverseRep[end];
    //printf("%c - %d - %d \n", reverseRep[end], end, start);
    start++;
    end--;
  }
  return 1;
}

Expecting output:
12 in binary: 1100

December 3rd, 2009, 07:29 PM

jwdonahue

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Quote:

Originally Posted by Neutralize

Sorry, I figured code pad would be easer.

For you maybe, but not for the folks you are asking for free help from.

What output are you getting?

December 3rd, 2009, 07:38 PM

jwdonahue

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That code won't even compile. When you are having trouble getting your program to compile you should say so and post your build log.

binaryRep and reverseRep are not big enough to be initialized with "0000". The string literal "0000" requires 5 character worth of storage.

Fix that, get it to compile, test it and let us know if have any more difficulties.

December 3rd, 2009, 08:23 PM

Neutralise

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Using gcc on a linux machine it is compiling - no problems.

Output I am getting is:
12 in binary: 11000011

Which is the the correct answer, but also the reverse at the end.
Im not sure why the 'bits' at the end are being added.

December 3rd, 2009, 08:33 PM

jwdonahue

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Quote:

Originally Posted by Neutralise

Output I am getting is:
12 in binary: 11000011

Which is the the correct answer, but also the reverse at the end.
Im not sure why the 'bits' at the end are being added.

That is because you are over-running the buffer. As I pointed out, you only have 4 characters of storage where you are trying to store 5. They just happen to be sequential. You need to turn up the warning level on your compiler. It should not accept the following code:

char binaryRep[4] = "0000";
char reverseRep[4] = "0000";

Change the size of those arrays to 5 and your program may actually work.

December 3rd, 2009, 08:37 PM

lackoblacko

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sorry about earlier
to display it correctly, you can either display each element in each array as a character as one solution or adjust the size of the array.

Comments on this post

jwdonahue disagrees: Wrong. He's printing number and then binaryRep. Notice there's two format specifiers in the format
string?

December 3rd, 2009, 08:45 PM

MadDogBrown

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Quote:

Originally Posted by lackoblacko

however, when you are displaying, you use

Code:

printf("%d in binary: %s \n", number, binaryRep);

therefore to display it correctly, you need to display each element in each array as a character.

As long as binaryRep is a NULL-terminated string, the %s format specifier will work as intended.

#10

December 3rd, 2009, 08:48 PM

jwdonahue

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Quote:

Originally Posted by BadDogBrown

As long as binaryRep is a NULL-terminated string, the %s format specifier will work as intended.

Yup. And therein lies the problem because binaryRep is not big enough to contain the terminating nul character.

#11

December 3rd, 2009, 08:48 PM

Neutralise

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jwdonahue,
Thankyou. I forgot about the terminating \0.

Is this an appropriate place to ask how to turn up the warning level on my compiler?

Thanks..

#12

December 3rd, 2009, 08:51 PM

jwdonahue

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Quote:

Originally Posted by Neutralize

Is this an appropriate place to ask how to turn up the warning level on my compiler?

Sure. I think it's -Wall, but I haven't used gcc in a while and my other neuron is on a break at the moment. Consult your man pages.

#13

December 3rd, 2009, 10:32 PM

MadDogBrown

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Quote:

Originally Posted by jwdonahue

Yup. And therein lies the problem because binaryRep is not big enough to contain the terminating nul character.

Am I a "Bad Dog" for referring to ascii nul as NULL?

Certainly that can't be worse than compiler vendors doing:
#define NULL 0

(Do they still do that?)

What is the current convention?

I can see how the usage of NULL can be ambiguous; perhaps "NULL character", or nul is the better way....

#14

December 3rd, 2009, 10:46 PM

jwdonahue

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Quote:

Originally Posted by MadDogBrown

#define NULL 0

(Do they still do that?)

What is the current convention?

I think they do still do that actually.

The standards language use the phrases null pointer and null character. Here's what the C standard says (as of 2005-05):

Quote:

Originally Posted by n1124.pdf

An integer constant expression with the value 0, or such an expression cast to type
void *, is called a null pointer constant.55) If a null pointer constant is converted to a
pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal
to a pointer to any object or function.

Conversion of a null pointer to another pointer type yields a null pointer of that type.
Any two null pointers shall compare equal

#15

December 3rd, 2009, 11:49 PM

Scorpions4ever

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Quote:

Originally Posted by MadDogBrown

Am I a "Bad Dog" for referring to ascii nul as NULL?

The basic idea of NULL is that it is a special value for pointer that is not the address of any function or successful allocation operation. Thus, you can never get NULL for a successful malloc(), calloc(), strdup() etc. and value of &any_function is guaranteed never to be NULL.

Now, NULL doesn't necessarily have to be at memory address 0 on the machine. It could be any address that is guaranteed never to be used by the computer for any legitimate data or code. In fact, there have been a few architectures where the NULL address was pointing somewhere else other than memory address 0.

Now for a final wrinkle, the C standard guarantees that whenever a pointer points to the constant 0
e.g.
int *foo = 0;
char *bar = 0;
etc.
this is converted by the compiler at compile time to point to that special NULL address. As we noted above, the actual address of NULL need not be mem. address 0, but the compiler will compile to code to point to wherever NULL is for that architecture.

Thus, #define NULL 0 will work when you do:
int *foo = NULL;
because the compiler will see that line written as:
int *foo = 0;
after the preprocessor replaces NULL with 0. As per the standard, assigning a constant 0 to a pointer will make the compiler point it to the actual NULL address on that machine.

With that said, it is never a good idea to interchange NULL pointer with the ASCII NUL character ('\0'). They are two different things. In particular, it is not a good idea to use NULL when you want to put '\0' in an array.

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Last edited by Scorpions4ever : December 3rd, 2009 at 11:52 PM.

Decimal to Binary

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