Branching with IF statements

The IF statement allows you to branch based on the result of a Boolean operation. The one-way branch format is:

If the Boolean expression evaluates to true, the statement executes. Otherwise, it is skipped.

The IF statement accepts only one statement. If you would like to branch to a compound statement, you must use a begin-end to enclose the statements:

There is also a two-way selection:

If the Boolean expression evaluates to FALSE, the statement following the else will be performed. Note that you may not use a semicolon after the statement preceding the else. That causes the computer to treat it as a one-way selection, leaving it to wonder where the else came from.

If you need multi-way selection, simply nest if statements:

Be careful with nesting. Sometimes the computer won't do what you want it to do:

The else is always matched with the most recent if, so the computer interprets the preceding block of code as:

You can get by with a null statement:

or you could use a begin-end block. But the best way to clean up the code would be to rewrite the condition.

This example illustrates where the not operator comes in very handy. If Condition1 had been a Boolean like: (not(a < b) or (c + 3 > 6)) and g, reversing the expression would be more difficult than NOTting it.

Also notice how important indentation is to convey the logic of program code to a human, but the compiler ignores the indentation.