This question is about named constants.

a) Why are named constants useful?

Answer: They reduce mistyping errors, they makes it clearer which
constant is being used and they make it easier to modify the program
later.


b) What is the difference between

    REAL, PARAMETER :: pi = 22.0/3.0
and

    REAL :: pi = 22.0/3.0

Answer: The first defines a named constant pi with value 22.0/3.0, the
second declares a variable named pi initialised to 22.0/3.0.

c) Is the following program fragment allowed?

    INTEGER, PARAMETER :: ZERO = 0
    ZERO = 1

Answer: No, because ZERO is a constant and cannot be changed.


d) Is the following program fragment allowed?

    INTEGER :: ONE = 1
    ONE = 0

Answer: Yes, since ONE is a variable. It can have any value.