I was trying out some point in poly math when I realized I have no idea how to check to see if a number is odd or even...Boy that sounds stupid Is there a function in the stdlib that can do it or will I need to work it out myself.

if( number % 2 )  number is oddelse  number is even 

I prefer

if(number & 1)  number is oddelse  number is even 

Edited by - VolkerG on May 28, 2000 7:35:59 AM

quote: Original post by VolkerG

I prefer

if(number & 1)  number is oddelse  number is even  

I prefer to use this too, because it''s faster (unless compilers convert number%2 to number&1 )

-my 2 cents-

Very good point, VolkerG and Arjan. As you can see, it was late and I wasn''t thinking too hard.

quote: Original post by Arjan

Original post by VolkerG

I prefer

if(number & 1)  number is oddelse  number is even   

I prefer to use this too, because it''s faster (unless compilers convert number%2 to number&1 )

-my 2 cents-

Well, I always assume the my compiler is clever enough to do this kind of optimization. Usually, MODs are computed via bitwise ANDs.

If prefer to keep the code mode readable…


Bye,

Karmalaa

In general a compiler will only optimize a modulus of a power of two to a mask if the variable that is being operated on is unsigned. If signed then the "equivalent" masking operation will not produce the same output for negative numbers. The modulus operator when performed on negative signed ints is supposed to be 0 or negative and a masking op will produce a positive number. Therefore the modulus operation will not be replaced with a mask by the compiler.

SiCrane, is there a way I can get your knowledge digitised, and copied into my brain? ;-)

It sure would be useful to know all those little things. I''ve only just gotten back into what the compiler optimises for you, and how to make sure your code is written so that is DOES do the optimisation.


#pragma DWIM // Do What I Mean!
~ Mad Keith ~

i think visual c automatically changes %2 to &1 (it''s listed in the optimization list)

- pouya
--------------
The trick to flight is to throw yourself at the ground and miss!!!

Here''s how I check for odd/even in C++:

class isEven {private:    int value;public:    even(int num) : value(num) { }    operator bool() { return 0 == (value % 2); }};class isOdd {private:    int value;public:    even(int num) : value(num) { }    operator bool() { return !isEven(value); }};int x = ...;if (isEven(x)) {    // x is even}else {    // x is odd}

Please be advised that this is a joke and I do not write my code using these!