XML CO538 Anonymous Questions and Answers Keyword Index

This page provides a keyword index to questions and answers. Clicking on a keyword will take you to a page containing all questions and answers for that keyword, grouped by year.

To submit a question, use the anonymous questions page. You may find the keyword index and/or top-level index useful for locating past questions and answers.

Keyword reference for bool

Question 11 (2009):

Submission reference: IN1810

How do you compare BOOLs, say in an IF statement? For example, if I have:

    INITIAL BOOL b IS TRUE:
    SEQ
      ...  code where the value of b can change
      IF
        b = TRUE   -- This always says "expected "?", found end of line"
          ...  do something

Can you tell me what I'm doing wrong?

Answer 11:

There is nothing wrong with your code fragment about which the compiler should complain ... unless within the hidden code "where the value of b can change", b is acttually re-declared as a channel! Please mail your seminar leader the whole code if your problem has not disappeared.

However, there is something about your code that is a bit weak. The condition(s) associated with an IF are, of course, BOOL(s). In your code, b is a BOOL (unless re-declared as something else!). Assuming it is a BOOL, then the expression:

        b = TRUE

is a clumsy way of saying:

        b

So, your code would be much neater as:

    INITIAL BOOL b IS TRUE:
    SEQ
      ...  code where the value of b can change
      IF
        b
          ...  do something

Last thought: your IF sturcture had better have some more conditions in case b turns out to be FALSE. Otherwise, there will be a run-time error – see Question 2 (2006) and Question 46 (2000).

Keywords: if , bool