Examining return types

Return types can often be very confusing for new programmers. The main hang-up for many of the students that I have taught is that they often have a difficult time understanding what a return type is. As we have seen, a return type is simply a value that a function returns. In very simple terms, the returned value is simply the output of a function.

Each function must be declared with a return type. This return type can be any data type that is supported by IEC 61131-3; for example, the integer data type from the Addition function. In all, a function can return exactly one value of the type the function was declared with. So, if you declared a function with a return type of INT, you must return an integer similar to what we did with the Addition function. As we saw with the Addition function, returning a value is as simple as assigning the function name to a statement, as we did in the preceding code snippet for invoking a function.

This is a simplistic...