How to test if exactly one condition is true?

Question

If I have a set of boolean variables in Pascal, how can I test if exactly one of them is True?

Answer 1

In Pascal you can do this:

if Integer(a) + Integer(b) + Integer(c) = Integer(true) then
    writeln("exactly one is true");

It's important to compare to Integer(true), since it could be different values in different versions of Pascal.