CODEWITHSUNDEEP
c
user6174425
user6174425

Reputation:

Converting ints to binary. I don't understand how this function works

void int_to_bin_digit(int in, int count, int* out)
{
   int mask = 1U << (count-1);       // LINE 1
   int i;
   for (i = 0; i < count; i++) 
   {
       out[i] = (in & mask) ? 1 : 0; // LINE 3 (I don't understand it )
       in <<= 1;                     // LINE 2
   }
}

I needed a function that converts ints to binary.I didn't know how to make one myself as I never used bit operators. I found this one on here it does its job.

let's say we call the function like this int_to_bin_digit( 67,8,out)

I understand that line 1 gives mask the value 128 (1000 0000) and that line 2 makes 67 (0100 0011) go like this (not sure about this one )

i=0  (0100 0011) 
-----------
i=1  (1000 0110) 
i=2  (0000 1100)  
i=3  (0001 1000)
i=4  (0011 0000) 
i=5  (0110 0000)
i=6  (1100 0000)
i=7  (1000 0000) (loop stops here )

(0000 0000) (so we never get to this one I guess)

Does line 3 compare only the first 1 and return 1 if it's ==1 and return 0 if it's !=1? how does it work exactly?

EDIT : https://davidzych.com/converting-an-int-to-a-binary-string-in-c/ after reading this. I see that we only compare the first 1 inside in with the first 1 inside mask I don't understand why it won't just return 1 in everycase, since both numbers are != 0. What makes the program only compares the first bits?

Upvotes: 1

Views: 76

Answers (1)

iehrlich
iehrlich

Reputation: 3592

Yes, your assumptions are almost all right.

LINE 1 is the mask of the count-th least bit. LINE 3 tests if such bit is set in your in number. The term & stands for the "bitwise and", where "and" operates on bits and is only equal to 1 when both operands are equal to 1, and "bitwise" means it is applied to respective pairs of bits of the operands. LINE 2 then proceeds to shift all the bits of in to the left, making n-th bit what was previously (n-1) bit.

But all in all, consider reading a tutorial about bitwise operations, this will make your life as a C programmer much easier.

Upvotes: 1

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