IF THEN statement
Standard: F77 F90 F95 F2003
  Example Program
[ construct-name : ] IF (expression) THEN

The expression must be a scalar Logical.
The IF-THEN statement begins an IF construct, marking the beginning of the THEN block. That block is executed if and only if the expression in the IF-THEN statement is true.

If this statement has a construct name, the corresponding END IF statement must have the same construct name, and intervening ELSE and ELSE IF statements at the same level may have the same construct name.
ELSE statement, ELSE IF statement, END IF statement, IF construct, IF statement