C Programming - Convert an integer to binary

Question

Hi guys - i was hopefully after some tips opposed to solutions as this is homework and i want to solve it myself

I am firstly very new to C. In fact i have never done any before, though i have previous java experience from modules at university.

I am trying to write a programme that converts a single integer in to binary. I am only allowed to use bitwise operations and no library functions

Can anyone possibly suggest some ideas about how i would go about doing this. Obviously i dont want code or anything, just some ideas as to what avenues to explore as currenty i am a little confused and have no plan of attack. Well, make that a lot confused :D

thanks very much

Answer 1

Tear it apart bit by bit. Use shifting. Handling more than one bit at a time can be done with a lookup table.

Answer 2

Think about about what you can do with bitwise operators.

E.g. you can test whether a bit is 1 or 0 like this:

int bit = value & 1;

You can also shift the bits in an int like this:

val = val >> 1;

To test the i'th bit in an int you can do this:

int bit = (value >> i) & 1;

Hopefully that's enough hints to get you started.

Answer 3

You could store the output in a character array

char output[33]; // for 32 bit integers, plus a null terminator if you need one
output[n] = '1';

or you could 'store' the output on the screen

printf("1");

though this could be argued as using a library functions

Answer 4

You might want to remember how you convert numbers to binary representations by hand. It might not be the most efficient way to do this, but it feels more natural than just playing with the shifting operators.

To convert a number into binary representation, you basically look which 2^i parts fit in that number and construct your binary number based on that.

Answer 5

I figure you should be done with your homework by now so here's a solution of mine. :)

I was just now trying to write an ascii-to-binary+binary-to-ascii converter in C, coincidentally. Binary to ascii was fairly simple with the strtol() function and all, and my code for converting a character (which is practically an int), was this:

void chartobinf(int c, FILE* out)
{
  size_t n = 8*sizeof(unsigned char);
  while (n-- > 0)
    fputs(((c >> n) & 1) ? "1" : "0", out);
}

This prints out a character (change parameter and sizeof types to suit your needs), in the correct order (which in my opinion is largest value first), as opposed to a lot of other solutions.

I especially like this solution because it is very short. Then again it doesn't save the value as a string or anything like that.

Edit: I guess one could also substitude the fputs() call with a

fputc(((c >> n) & 1) ? '1' : '0', out);

Might be microseconds faster? Dunno.