Help with running code only every other iteration

I have just started programming in lua (Computercraft) but have a problem:

I have a for loop where there is a bit of code i only want to run ever other time it runs through the loop. How can i do that?

Split into new topic.

The usual manner of doing this is to include a conditional block inside your loop that looks a bit like:

if i % 2 == 0 then
 --do things on even numbered iterations
end