Initialisation

When a program is loaded into the computers memory, the contents of declared variables are normally undefined, it is clearly useful to override this and give variables useful initial values. For example,

    INTEGER          :: i = 5, j = 100
    REAL             :: max = 10.D5
    CHARACTER(LEN=5) :: light = 'Amber'
    CHARACTER(LEN=9) :: gumboot = 'Wellie'
    LOGICAL          :: on = .TRUE., off = .FALSE.

For CHARACTER variables, if the object and initialisation expression are of different lengths then either:

• the object will be padded with blanks on the RHS, or
• the initialisation expression will be truncated on the right so it will fit.

Variables can be initialised in a number of ways

• PARAMETER statements,
• DATA statements,
• type declaration statements (with an =< expression >) clause.

Limited expressions known as initialisation expressions can also be used in type declaration statements. These expression must be able to be evaluated when the program is compiled -- if you can't work out the values then neither can the compiler. Initialisation expressions can contain PARAMETER s or literals. Arrays may be initialised by specifying a scalar value or by using a conformable array constructor, (/.../).

    REAL, PARAMETER :: pi = 3.141592
    REAL :: radius = 3.5
    REAL :: circum = 2 * pi * radius
    INTEGER :: a(1:4) = (/1,2,3,4/)

In general, intrinsic functions cannot be used in initialisation expressions, however, the following intrinsics may be used:

• REPEAT,
• RESHAPE,
• SELECTED_INT_KIND,
• SELECTED_REAL_KIND,
• TRANSFER,
• TRIM.
• LBOUND,
• UBOUND,
• SHAPE,
• SIZE,
• KIND,
• LEN,
• BIT_SIZE,
• numeric inquiry intrinsics, for, example, HUGE, TINY, EPSILON.

In this context the arguments to these functions must be initialisation expressions.