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fortran .HLP

Aggregate_Reference

An aggregate reference resolves itself to a reference to a structured data item (a record structure or substructure). For example:

Data Declarations:

STRUCTURE /STRA/ INTEGER INTFLD, INTFLDARY (10) END STRUCTURE . . . STRUCTURE /STRB/ CHARACTER*20 CHARFLD INTEGER INTFLD, INTFLDARY (10) STRUCTURE STRUCFLD COMPLEX CPXFLD, CPXFLDARY (10) END STRUCTURE RECORD /STRA/ RECFLD, RECFLDARY (10) END STRUCTURE . . . RECORD /STRB/ REC, RECARY (10)

Reference Examples:

REC --- Is a record name.

RECARY(1) --- Is a record array reference.

REC.RECFLD --- Is a reference to a substructure.

REC.RECFLDARY(1) --- Is a reference to a substructure array element.

RECARY(1).RECFLD --- Is a reference to a substructure in a record array element.

RECARY(1).RECFLDARY(1) --- Is a reference to a substructure array element in a record array.

Arrays

An array is a group of contiguous storage locations associated with a single symbolic name, the array name. The individual storage locations, called array elements, are referred to by a subscript appended to the array name. An array can have from 1 to 7 dimensions. The Fortran statements that establish arrays are: type declaration statements, the DIMENSION statement, and the COMMON statement.

The data type of an array is specified in the same way as the data type of a variable; either implicitly by the first letter of the name or explicitly by a type declaration statement.

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Array_Name_Reference

An array name reference resolves itself to the name of an array with no subscripts after the array name. For example:

Data Declarations:

INTEGER INT, INTARY (10) . . . STRUCTURE /STRA/ INTEGER INTFLD, INTFLDARY (10) END STRUCTURE . . . STRUCTURE /STRB/ CHARACTER*20 CHARFLD INTEGER INTFLD, INTFLDARY (10) STRUCTURE STRUCFLD COMPLEX CPXFLD, CPXFLDARY (10) END STRUCTURE RECORD /STRA/ RECFLD, RECFLDARY (10) END STRUCTURE . . . RECORD /STRB/ REC, RECARY (10)

Reference Examples:

INTARY --- Is a numeric or character array.

RECARY --- Is an array of records.

REC.INTFLDARY --- Is a numeric or character array field of a record.

REC.RECFLDARY --- Is an array of substructures within a record.

RECARY(1).INTFLDARY --- Is a numeric or character array field of a record array element.

RECARY(1).RECFLDARY --- Is an array of substructures within a record array element.

Constants

A constant is a fixed value. The value of a constant can be a numeric value, a logical value, or a character string. There are seven types of constants: integer, real, complex, bit, logical, character, and Hollerith. Bit and Hollerith constants have no data type; they assume a data type that conforms to the context in which they are used.

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Expressions

An expression represents a single value. An expression can consist of a single constant, variable, record element, array element, or function reference; or combinations of these data items plus certain other elements, called operators. Operators specify computations to be performed on the values of the data items and a single result is obtained.

Expressions are classified as arithmetic, character, relational, or logical. Arithmetic expressions produce numeric values; character expressions produce character values; and relational and logical expressions produce logical values.

The data components of an expression must be compatible and must be joined by compatible operators. Expressions are evaluated one operator at a time according to the rules of precedence. The ranking assigned to each data type is as follows:

Data Type Ranking --------- ------- BYTE, LOGICAL*1, INTEGER*1 1 (lowest) LOGICAL*2 2 LOGICAL*4 3 INTEGER*2 4 INTEGER*4 5 REAL*4 (REAL) 6 REAL*8 (DOUBLE PRECISION) 7 REAL*16 8 COMPLEX*8 (COMPLEX) 9 COMPLEX*16 (DOUBLE COMPLEX) 10 (highest)

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Records

The DEC Fortran record handling capability enables you to declare and operate on multi-field records. A DEC Fortran record is a named data entity, consisting of one or more fields, that you create in your program. Creating a record requires both a structure declaration (to describe the fields in the record) and a RECORD statement to establish the record in memory.

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Scalar_Reference

A scalar reference is a scalar variable, scalar record field, array element, constant, character substring, or expression that resolves into a single, typed data item. For example:

Data Declarations:

Reference Examples:

INT --- Is a numeric variable.

INTARY(1) --- Is a numeric array element.

REC.INTFLD --- Is a numeric field.

REC.INTFLDARY(1) --- Is a numeric element of an array field.

CHARVAR(5:10) --- Is a substring expression of a character variable.

REC.CHARFLD(5:10) --- Is a substring expression of a character field.

Note: A scalar memory reference is the same as a scalar reference, excluding constants and expressions.

Substrings

A character substring is a contiguous segment of a character variable, character array element, or character field reference. It has one of the following forms:

v([e1]:[e2]) OR a(s[,s]...)([e1]:[e2])

v Is a character variable name.

a Is a character array name.

s Is a subscript expression.

e1 Is a numeric expression specifying the leftmost character position of the substring.

e2 Is a numeric expression specifying the rightmost character position of the substring.

NOTE: 1 .LE. e1 .LE. e2 .LE. length-of-v must hold true

Types

The Fortran data types are as follows:

o Integer - A whole number

o REAL (REAL*4) - A single-precision floating-point number (a whole number or a decimal fraction or a combination)

o DOUBLE PRECISION (REAL*8) - A double-precision floating-point number (like REAL*4, but with twice the degree of accuracy in its representation)

o REAL*16 - A quad-precision floating-point number (like REAL*4, but with four times the degree of accuracy in its representation.)

o COMPLEX (COMPLEX*8) - A pair of REAL*4 values representing a complex number (the first part of the number is the real part, the second is the imaginary part)

o COMPLEX*16 (DOUBLE COMPLEX) - Similar to complex, but with twice the degree of accuracy in its representation (its real or imaginary part must be a REAL*8)

o Logical - A logical value, .TRUE. or .FALSE.

o Character - A sequence of characters

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Variables

A variable is represented by a symbolic name that is associated with a storage location. The value of the variable is the value currently stored in that location; the value can be changed by assigning a new value to the variable.

Variables, like constants, are classified by data type. When data of any type is assigned to a variable, it is converted, if necessary, to the data type of the variable. You can establish the data type of a variable by type declaration statements, IMPLICIT statements, or predefined typing rules.

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