IF construct
Standard: F77 F90 F95 F2003
 Example Program
[ else-if-stmt
    block ]...
[ else-stmt
    block ]
The IF construct selects a single block of statements for execution. The conditions (expressions) in the IF THEN statement and the ELSE IF statements are evaluated in order until one has the value true; if this is found, the block following that statement is executed. If all the conditions are false, the ELSE block will be executed if present; with all conditions false and no ELSE block, control will be transferred to the END IF statement.
ELSE statement, ELSE IF statement, END IF statement, IF statement, IF THEN statement