how to loop through the digits of a binary number?

Question

I have a binary number 1011011, how can I loop through all these binary digits one after the other ?

I know how to do this for decimal integers by using modulo and division.

Solution 1

int n = 0x5b; // 1011011

Really you should just do this, hexadecimal in general is much better representation:

printf("%x", n); // this prints "5b"

To get it in binary, (with emphasis on easy understanding) try something like this:

printf("%s", "0b"); // common prefix to denote that binary follows
bool leading = true; // we're processing leading zeroes
// starting with the most significant bit to the least
for (int i = sizeof(n) * CHAR_BIT - 1; i >= 0; --i) {
    int bit = (n >> i) & 1;
    leading |= bit; // if the bit is 1, we are no longer reading leading zeroes
    if (!leading)
        printf("%d", bit);
}
if (leading) // all zero, so just print 0
    printf("0");

// at this point, for n = 0x5b, we'll have printed 0b1011011

Solution 2

Expanding on Frédéric and Gabi's answers, all you need to do is realise that the rules in base 2 are no different to in base 10 - you just need to do your division and modulus with a divisor 2 instead of 10.

The next step is simply to use number >> 1 instead of number / 2 and number & 0x1 instead of number % 2 to improve performance. Mind you, with modern optimising compilers there's probably no difference...

Solution 3

You can use modulo and division by 2 exactly like you would in base 10. You can also use binary operators, but if you already know how to do that in base 10, it would be easier if you just used division and modulo

Solution 4

Use an AND with increasing powers of two...

Solution 5

In C, at least, you can do something like:

while (val != 0)
{
   printf("%d", val&0x1);
   val = val>>1;
}

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Comments

[Attilah]

thanks, i just realized that i could do modulo and division by 2.

[Gabi Purcaru]

@Attilah you can do that in any base actually, even base 16 (but you would have to manually replace 10 with A and so on) :)

[Matt Joiner]

Note in advance: You want to include limits.h, stdbool.h (requires C99), stdio.h if you try to build this. If these aren't available for whatever reason, let me know and I'll modify the code to conform to your respective system.

[R.. GitHub STOP HELPING ICE]

There is a difference if number is signed. The compiler has to go to extra trouble to meet C's inept definition of division ((-3)/2==-1, not -2 like it should). Of course in many cases you should fix this just by using unsigned types rather than resorting to bitwise operations, but if your value really is signed and you want number%2 to yield -2 when number is -3, number&1 is the way to go. Keep in mind bitshifts are not well-defined for negative numbers though.

[Mac]

Right you are! Good point... I have a bad habit of thinking unsigned when dealing with bit twidling.

[Nathan S.]

Note that you can just say printf("0b"); no need for the %s and string argument.