How do you loop a fraction

How come when I attempt to iterate through a loop (for or while) I am unable to increase it by a fraction (let's say 0.5). If I start with a variable defined as 0 then ask it to increase by 1 each time (++) up until 5 it works fine. However, if I ask it to increase by 0.5 it causes an infinite loop. Clearly there is an error with the incremental formula.