I have a while loop, with start, stop, & step digital controls, if Start = -0.2, stop -0.8 and step = 0.05, when the prog gets to increment = stop = -0.8, it produces a false, when it is showing that they are equal! See prog attached.
Because they're not equal. It has to do with binary representation of floating point numbers. Go to LabVIEW FAQ for more details and techniques on how number comparison can be correctly performed.
The reason this is happening is because you are using floating point numbers. Floating point numbers are not always exactly represented. To prove this to yourself you can do two things. First, put an indicator at the output of the Subtract function. Then, set the "digits of precision" of all your controls and indicators to something large - say 20. What you will notice is that -0.8 is really something like -0.800000000000000044000000.
The lesson from all this is to either use integers when comparing to stop a loop, or use >= and =< instead of just =.
If you subtract the two values you're comparing, add an indicator to the subtract output, and change the format of the indicator (by right-clicking on it) to display 20 decimal points, you'll see that the numbers aren't what you expect. The attached VI shows one way to implement your loop.
