FORTRAN, Data, Variables
*Conan The Librarian
A variable is a data object whose value can be changed at any point
in a program. It can be any of the following:
o A scalar name
A scalar is a single object that has a single value; it can be
of any intrinsic or user-defined type.
o An array name
An array is a collection of scalar elements of any intrinsic or
derived type. All elements must be have the same type and kind
o A subobject designator
A subobject is part of an object. The following are
An array element
An array section
A structure component
For example, B(3) is a subobject (array element) designator for
array B. A subobject cannot be a variable if its parent object
is a constant.
The name of a variable is associated with a single storage
Variables are classified by data type, as constants are. The data
type of a variable indicates the type of data it contains,
including its precision, and implies its storage requirements.
When data of any type is assigned to a variable, it is converted to
the data type of the variable (if necessary).
A variable is usually defined in a type declaration statement or
DATA statement. But during program execution, events can occur to
cause variables to be defined or redefined (such as assignment
statements and READ statements), or undefined (such as an I/O
Scalar variables are assigned data types explicitly in type
declaration statements or IMPLICIT statements, or they can have
implicit data types.
By default, all variables with names beginning with I, J, K, L, M,
or N are assumed to be integer variables. Variables beginning with
any other letter are assumed to be real variables.
Names beginning with a dollar sign ($) are implicitly INTEGER.
You can override the default data type implied in a name by
specifying data type explicitly in either an IMPLICIT statement or
a type declaration statement.
Note: You cannot change the implicit type of a name beginning with
a dollar sign in an IMPLICIT statement.
Type declaration statements explicitly specify the data type of
scalar variables. For example, the following statements associate
VAR1 with an 8-byte complex storage location, and VAR2 with an
8-byte double-precision storage location:
DOUBLE PRECISION VAR2
You can explicitly specify the data type of a scalar variable only
An explicit data type specification takes precedence over the type
specified by an IMPLICIT statement. If no explicit data type
specification appears, any variable with a name that begins with
the letter in the range specified in the IMPLICIT statement becomes
the data type of the variable.
Character type declaration statements specify that given variables
represent character values with the length specified. For example,
the following statements associate the variable names INLINE, NAME,
and NUMBER with storage locations containing character data of
lengths 72, 12, and 9, respectively:
CHARACTER NAME*12, NUMBER*9
In single subprograms, assumed-length character arguments can be
used to process character strings with different lengths. The
assumed-length character argument has its length specified with an
asterisk, for example:
The argument CHARDUMMY assumes the length of the actual argument.