Fortran - Decisions

Decision making structures require that the programmer specify one or more conditions to be evaluated or tested by the program, along with a statement or statements to be executed, if the condition is determined to be true, and optionally, other statements to be executed if the condition is determined to be false.

Following is the general form of a typical decision making structure found in most of the programming languages:
Fortran provides the following types of decision making constructs.

Statement	Description
If… then construct	An if… then… end if statement consists of a logical expression followed by one or more statements.
If… then...else construct	An if… then statement can be followed by an optional else statement, which executes when the logical expression is false.
if...else if...else Statement	An if statement construct can have one or more optional else-if constructs. When the if condition fails, the immediately followed else-if is executed. When the else-if also fails, its successor else-if statement (if any) is executed, and so on.
nested if construct	You can use one if or else if statement inside another if or else if statement(s).
select case construct	A select case statement allows a variable to be tested for equality against a list of values.
nested select case construct	You can use one select case statement inside another select case statement(s).