This statement has the following look:
if boolean_expression then
statement
or with an alternative statement:
if boolean_expression then
statement1
else
statement2
The if ... then statement consists of a boolean expression
and a statement, which is conditionally executed if the
evaluation of boolean_expression yields true.
If if ... then ... else is concerned,
statement1 is executed depending on boolean_expression being
true, otherwise statement2 is executed alternatively. Note: the
statement before else must not finish with a semicolon.