As odd is even

Many times since I started programming I have had to write some sort of functionality to test if a number is odd.

It is odd that I woke up thinking about this and all the different ways I have implemented this test as my programming skill and understanding improved, so here's a whistle stop tour. I think its interesting to see the way thought processes change...

Ok, so when I was 15, my good friend Tim was pondering the same question, my answer was to use a float and an int.

Say that we want to test if '5' is even.

int a = 5;
float b = 5;
a = a / 2;
b = b / 2;
if(b!=a) // If they are not equivalent then the number is ODD!

As you can see, this is rather in efficient but at the time, it worked.

A little while later we learned about the % operator, so we can do something like this:

int a = 5;
int b = 5 % 2;
if(b>0) // If b is > 0 then the number is ODD!

Then I went to cern, worked for a while on some pretty high performance C and ended up writing this without thinking about it:

#define isEven(x) x&0x1

Learning is fun :-P