The two forms of conditional statement are
Conditionalstatement ::=
IF
Condition
THEN
Consequence
IF
Condition
THEN
Consequence
ELSE
Alternative
Consequence ::=
Simplestatement
Label : Consequence
Alternative ::=
Statement
If the condition is true, the consequence is obeyed. If the condition is false and ELSE is present, the alternative is obeyed. If the condition is false and no ELSE is present, the conditional statement has no effect beyond evaluation of the condition.