VMS Help FORTRAN, Data, Expressions  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  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)

1 - Arithmetic

  Arithmetic expressions contain numeric data such as variables,
  record elements, array elements, constants, function references,
  and arithmetic expressions enclosed in parentheses.  The expression
  evaluates to a numeric value.  The numeric operators are as
  follows:

       OPERATOR    RANK        DESCRIPTION
          **        1          exponentiation (evaluated
                                   right to left)
          *         2          multiplication
          /         2          division
          +         3          addition
          -         3          subtraction

  You can use parentheses to force an order of evaluation.

2 - Character

  Character expressions consist of character elements and character
  operators.  Evaluation of a character expression yields a single
  value of character data type.  A character element can be a
  constant, variable, record element, array element, substring,
  expression (optionally enclosed in parentheses), or a function
  reference.

  A character expression has the form:

    character element[//character element]...

  The concatenation operator (//) is the only character operator.
  Concatenation is from left to right.

3 - Logical

  Logical expressions can contain logical and integer data such as
  variables, record elements, array elements, constants, function
  references, expressions enclosed in parentheses, and relational
  expressions.  The expression evaluates to a logical value using the
  following operators:

       OPERATOR       PRECEDENCE
        **             First (Highest)
        *,/            Second
        +,-,//         Third
        Relational
         Operators     Fourth
        .NOT.          Fifth
        .AND.          Sixth
        .OR.           Seventh
        .XOR.          Eighth (Lowest)
        .NEQV.         Eighth
        .EQV.          Eighth

4 - Relational

  Relational expressions consist of either two arithmetic or two
  character expressions separated by relational operators.  The
  expression is reduced to a logical value (true or false).

        OPERATOR      DESCRIPTION
         .LT.          Less than
         .LE.          Less than or equal to
         .EQ.          Equal to
         .NE.          Not equal to
         .GT.          Greater than
         .GE.          Greater than or equal to

  Expressions of COMPLEX data type can use only .EQ. and .NE.
  operators.