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

if BooleanExpression then   StatementIfTrue;

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:

if BooleanExpression then begin   Statement1;   Statement2 end;

There is also a two-way selection:

if BooleanExpression then   StatementIfTrue else   StatementIfFalse;

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:

if Condition1 then   Statement1 else   if Condition2 then     Statement2   else     Statement3;

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

if Condition1 then   if Condition2 then     Statement2 else   Statement1;

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

if Condition1 then   if Condition2 then     Statement2   else     Statement1;

You can get by with a null statement:

if Condition1 then   if Condition2 then     Statement2   else else   Statement1;

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

if not Condition1 then   Statement1 else   if Condition2 then     Statement2;

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.