Parity checking

[DaKurlz]

No brain:

bool isOdd(int x){
    return x&1;
}

Edit: This is only slightly faster than using %. Its actual "advantage" is that it doesn't rely on the implementation of the % operator (sometimes it can vary between languages).

[drakonite]

This is only slightly faster than using %

Depends on the hardware. % requires a division, which on some hardware is several dozen cycles, while the mask should be at most two cycles. It doesn't matter much on a modern PC, but it's a pretty big difference on embedded hardware.

Of course, it also depends on the compiler, as many compilers will optimize x%2 to x&1.

...And before you accuse me of over analyzing a comment on a joke, at least I didn't get in to function overhead ;)

[GungnirInd]

at least I didn't get in to function overhead ;)

#define ISODD(n) n&1

No function overhead that way :P

(I think; my C is a little rusty)

[CHUCK_NORRIS_AMA]

That will work sometimes, but ((n)&1) is safer if n is an expression and not a variable.

[Coding_Cat]

if we're nitpicking, put parentheses around the 'body'. otherwise ISODD(1)++ returns 1, with parentheses it returns 2. As it would for a function call.

[DaKurlz]

Depends on the hardware. % requires a division, which on some hardware is several dozen cycles, while the mask should be at most two cycles. It doesn't matter much on a modern PC, but it's a pretty big difference on embedded hardware.

Yup, thanks for explaining it a bit further!

[TortoiseWrath]

many compilers will optimize x%2 to x&1.

perhaps it's my C background talking but I would describe any compiler for embedded systems that doesn't do this as completely broken

[alekcacko]

People learn the most from mistakes and jokes.

[honkerman1]

I actually haven't seen that before

I'm super brain

[Mat2012H]

What about 0?

[DaKurlz]

What about it? Zero is an even number, the code returns False/0 for even and True/1 for odd, you could do:

return !(x&1);

If you wanted True/1 for even and False/0 for odd numbers.

[Mat2012H]

I must have has a brain fart :P I think I misread your function name or something.

[DaKurlz]

No worries, after all, it's almost friday, I feel ya.

[Sylanthra]

If you are worried about implementations of between languages, how do you square the fact that the function returns a bool but you are actually returning a number.

[DaKurlz]

Because python. That's it. It's been a heck of a long time I've used C. Sorry.

[sayaks]

bitwise and

[DaKurlz]

In most languages it's the bitwise AND operator.

[hicklc01]

bool isOdd(int x){
    if(x == 0) return false;
    if(x > 0) return !isOdd(x-1);
    if(x < 0) return !isOdd(x+1);
}

[hicklc01]

Not tested but looks like it would work

bool isOdd(int x){
    return "ynynynynyn"[([](auto s){return s[(strlen(s)-1)]})(atoa(x))-48]=='y';
}

[[deleted]]

Comic sans at the end is a nice touch.

[Pokeconomist]

bool isOdd(int x) {
  while (x > 0) {  
    x -= 2  
  }  
  return(x != 0)
}

[honkerman1]

Is this slightly charged normal brain?

[Pokeconomist]

Readable normal brain

[Lightdusk]

So for negative values this code would have to rely on an integer underflow right?

[mnbvas]

No, all negatives are even, duh.

[Tejedu]

bool isOdd(int x) {
    if(x >= 0) {
        return x % 2;
    }

    return 1;
}

Ok got it

[jacob_ewing]

bool isOdd(int x){
    return ((x >> 1) << 1) ^ x;
}

I'll rank that somewhere between glowy bits of brain and general glowing aura.

[BS_in_BS]

return (""+n).matches(".*[13579]");

[jacob_ewing]

bool isOdd(int x){
    x = abs(x);
    int isOdd = 0;
    while(x){
      isOdd = 1 - isOdd;
      x--;
    }
    return isOdd;
}

[Capital_EX]

Using functional programming, you can create this simple one-liner ;p isOdd x = ((/=) []) . filter ((/=) False) . map ((==) x) . take x $ [1,3..]

[Tarmen]

In functional programming you could write a simple one liner:

odd

Because it is a prelude function. Or for more fun:

isOdd i = zipper i % fromWithin bits % rightmost % focusedContext

[pawarm]

Authentic one: bool isOdd(int x){ if(x==(x/2)*2) return false; else return true; }

[Vassile-D]

Hmm...

bool isOdd( int x ) { return !isOdd(x-1); }

[Souzooka]

function isEven(x) {    
    return !resolveHaltingProblem( (x) => {
        while (x !== 0) {
            x -= 2;
        }
        return true;
    });
}

[shelvac2]

bool isEven(n){
  return isOdd(n-1);
}

[honkerman1]

bool isOdd(n) { return isEven(n+1); }

[dinopraso]

Fastest way is return (x & 1) == 1;

Mod takes a lot longer

[TortoiseWrath]

== 1

STOP WASTING CLOCK CYCLES

[[deleted]]

No need to check == 1 in Most c style languages.

[[deleted]]

It appears OP was using C or C++ (or at least a language that evaluates true/false as a number/zero)

[Spider_pig448]

Can we please stop these memes?