Greater than & lesser than works reversed in an if-statement that breaks

Hello out there!

I have quite a problem figuring how to solve a problem that exists in a main-script of mine in Matlab-programming. I've made three functions that my main-script is based upon. I've startede with a while true statement. You can see the code below this:

Best regards

Kristian

[James Tursa]

@Kristian: It is an abuse of this site and a disservice to the readers and contributors for you to edit out the content of your question after you have received answers.

Answer 1

[Stephen23]

Your arguments to && are reversed. Read the documentation for the && operator and you will find that it evaluates from left to right. So first it evaluates this:

0 < beamLength

which if beamLength happens to be NaN (such as if the input is not a valid number) then the comparison is false and the next term is never evaluated: the results will always be false:

>> 0 < NaN
ans = 
      0

To resolve this you could try reversing the order:

~isnan(beamLength) && 0 < beamLength

But a better solution would be to not use break at all, and make the while-loop condition do the comparison for you:

val = NaN;
while ~(isfinite(val) && val>0)
    val = str2double(input('enter a value: ','s'));
end

this will keep prompting until a positive number has been entered.