What is an odd number?

[silex]

If anyone could answer the question, I'll be glad.
What is an odd, even number?
What is the difference between odd and even numbers?

[redhead]

Even can be devided by two, which actualy includes the number 0.

[silex]

Thanks redhead
So checking if a number is even should be:

number % 2
if mod = 1 then number is odd
else mod = 0 then number is even
I understand.

[sdeming]

Another more optimal approach is to simply check the 1 bit.

In C++ it looks like this:

if (number & 1 == 1) {
  // number is odd
}
else {
  // number is even
}

[silex]

what does the '&' do?

[ender]

The & is a bitwise AND function. The AND function returns true (or 1 in the case of bits) if both bits are 1. It returns 0 in every other case. In this example, it is used as a mask. You can stop here if you already understand this, and I am sorry if I am teaching the teachers... but I will continue if you do so wish.

If you have a byte (take the number 5: 0101) and you only want the last bit (1) you can use a bitmask to find it by using the AND operator. You would use the mask 0001. If you AND this with 5: 0101 & 0001 .. all the bits in positions 2 through 4 are set to 0, with the first be being 1 (0001). Remember, any two bits that are not 0 get set to 0 by the AND function.

In this case, this is what we want. If a number is odd, it will have a 1 in the first bit position (5: 0101) while even numbers don't (4: 0100). This is true for all odd/even numbers, because only 2^0 is odd (1). Therefore, we can use a bitmask of 1 to see whether this bit is set: someNumber & 1 = 0000x where x is 1 or 0, 'odd' or 'even'.

I'm pretty sure you'd have to take care of the edge case where the user supplies 0, as it is not really even or odd. I guess it is considered even though, from a previous post I don't think this algorithm would work on negative numbers though. I guess modulus wouldn't either, I'll have to test it.

Hope this helps!

PS: There is also OR and XOR operators. These could be discussed at another time. OH.. I think I feel my first article coming on! Well, that is, if it has not been done before.

[silex]

Thanks ender.
I understand this, your post was really helpful.

I got some C excercises, and I try to write a program that:
1. Gets an int array
2. Using some loops, it will reverse the numbers in array to display them backwards // I don't know if loops are good for this task//
3. Write the reversed array in new int array

give me some directions or tips, these would be really helpful.

[Androto]

lol, i had to do the same thing but for words. i had to reverse the words then compare them to the original words to see if they were palindromes. I don't have the code with me, but yes, i did use a loop.