Thread: Create a string in binary from a decimal number

Hi.

My first post here.

I am attempting to take a decimal number (0-255) and convert it to a binary string.

Something that looks like 0b01010101 for example.

Code:

//CONVERT DECIMAL TO BINARY FUNCTION
void tobinary(char str[11], int num)
{
    int i;
    bool bin;
    
    str[0] = '0';
    str[1] = 'b';
    
    for (i=2; i<10; i++)
    {
        bin = (num & 0x80);
        if (bin = 1)
        {
            str[i] = '1';
        }
        else 
        {
            str[i] = '0'; 
        }
        num <<= 1;   
    }
    str[i++] = '\0';
}

This is what i have written, but the string just comes out as 0b11111111, no matter what number i give it.

Not sure what i have done wrong. Is there anything obvious here to the more experienced eye?

Do you know the difference between assignment "=" and comparison "=="?

By the way your compiler should be able to help you solve this issue, insure your compiler is set up to generate warnings and never ignore those warnings.

From my compiler: "main.c|31|warning: suggest parentheses around assignment used as truth value [-Wparentheses]|"

if(bin = 1)
The equal operator is ==, not =.

Another thing: All numeric representations in a computer are binary. When you do

Code:

int x = 10;

This "decimal" 10 is encoded in binary and put in memory (or register) as a binary value. So, you can isolate the bits "directly" (avoiding divisions):

Code:

void int2str( char *s, unsigned char n )
{
  int i = 0;

  while ( i < 8 )
  {
    *s++ = '0' + ( ( n & 0x80 ) != 0 );
    n <<= 1;
    i++;
  }
}

Thanks guys.
I have been coding for about 3 days!!

I didnt see the = and == differences when looking for similar examples of what i was attempting to do.

The == has fixed the function tho and it does as i expect it to now.

Originally Posted by flp1969

Another thing: All numeric representations in a computer are binary. When you do

Code:

int x = 10;

This "decimal" 10 is encoded in binary and put in memory (or register) as a binary value. So, you can isolate the bits "directly" (avoiding divisions):

Code:

void int2str( char *s, unsigned char n )
{
  int i = 0;

  while ( i < 8 )
  {
    *s++ = '0' + ( ( n & 0x80 ) != 0 );
    n <<= 1;
    i++;
  }
}

This looks much more condensed than how i have gone about it.
Does this method have much benefit in speed? Or is it just less typing?

Originally Posted by Kisen

This looks much more condensed than how i have gone about it.
Does this method have much benefit in speed? Or is it just less typing?

In essence it is the same thing. I've only notice that any comparison results in 0 or 1 (not other values)... The if:

Code:

bin = n & 0x80;  // isolate bit 7.
if ( bin == 1)
  s[i] = '1';
else
  s[i] = '0';

Can be substituted by a single line:

Code:

s[i] = '0' + ( ( n & 0x80 ) != 0 );

As for the generated code by the compiler, with optimizations turned on, both codes are the same.

And, since s points to the beggining of the string, I use it...

BTW: There is an error in my routine. Before returning it should have:

Code:

  ...
  *s = '\0';  // puts the end of string mark.
}

what kind of c extensions do you use for gcc compiler? My compiler only quits with error message, unknown type bool instead of _Bool and so on.
Maybe compiler extension option will solve this error?

Originally Posted by Yamyam

what kind of c extensions do you use for gcc compiler? My compiler only quits with error message, unknown type bool instead of _Bool and so on.
Maybe compiler extension option will solve this error?

If your compiler is using C Standard C99 or later, the you could add:

Code:

#include <stdbool.h>

which would allow the use of "bool" in your code, and provide the two values allowed in a bool variable, "true" and "false".

are setting warning level high=warnings is reported as errors something to recommend when newbie or when nasty hard to find bugs like "=" when it should be "==" ?

IMO, using high warning levels is something to recommend on most occasions.

By the way I don't find the '=' versus "==" to be a hard to find bug, however setting your compiler to generate a message for this problem really makes it a trivial issue.