if Boolean_expression then statement
or with an alternative statement:
if Boolean_expression then statement1 else statement2
The if ... then statement executes statement1 depending on Boolean expression being true. If else is specified, it continues executing statement2 instead.
if is defined in ISO 7185 Pascal and supported by all known Pascal variants.
program IfDemo; var Foo, Bar: Boolean; begin Foo := True; Bar := False; if ((1 = 1) or (2 = 3)) and (Foo = not Bar) then begin { This is executed if either Foo is true but not Bar or vice versa } WriteLn ('Either Foo or Bar is true.'); if Bar then WriteLn ('You will see this text if Bar is true.') end else { This whole `else' branch is not executed } if 1 = 1 then if True = False then WriteLn ('This text is never written on screen.') else { Note: This ``else'' belongs to ``if True = False'' } WriteLn ('This text is never written on screen as well.') else { Note: This ``else'' belongs to ``if 1 = 1'' } WriteLn ('Nor is this.') end.