Constants (Parameters)

Symbolic constants, oddly known as parameters in Fortran, can easily be set up either in an attributed declaration or in a PARAMETER statement (it is recommended that the attributed form be used):

    INTEGER price_of_fags            ! F77 style - not recommended
    PARAMETER (price_of_fags = 252)  ! F77 style - not recommended
    REAL, PARAMETER ::  pi = 3.14159 ! F90 style

CHARACTER constants can assume their length from the associated literal (LEN=*), they can also be declared to be fixed length:

    CHARACTER(LEN=*), PARAMETER :: son = 'bart', dad = "Homer"

Parameters should be used:

• if it is known that a variable will only take one value;

  The variable is forced to be unchanged throughout the program. If any statement tries to change the value an error will result.

• for legibility where a `magic value' occurs in a program such as ;

  Symbolic names are easier to understand than a meaningless number.

• for maintainability when a `constant' value could feasibly be changed.

  The value of the constant can be adjusted throughout the program by changing 1 line.

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