Copyright (c) 1994 J. Adams, W. Brainerd, J. Martin, and B. Smith.
All rights reserved.
This file may not be copied without permission of the authors.

84 Source Form

There are two source forms that may be used to write Fortran 90 programs. One is the form used in Fortran 77 and is called fixed source form. The other, free source form, is new in Fortran 90 and is described here.

Examples:

PROGRAM NICE

   !  This is a nice way to write a program!
      PRINT *
      PRINT *,  &
            12.0 + 34.6

END PROGRAM NICE

                   PROGRAM &
UGH  ! This is a terrible way to write a program!
          PRINT                                              &
              *;   PRINT &
     *     ,                &
               12.0         +&
    34.6
        END

Tip: Pick a consistent style for writing programs, using a consistent amount of indentation, placement of comments, etc.

It is possible to write programs in a way that is acceptable as both free source form and fixed source form. The rules are:

  1. Put labels in positions 1-5.
  2. Put statement bodies in positions 7-72.
  3. Begin comments with an exclamation ( ! ) in any position except 6.
  4. Indicate all continuations with an ampersand in position 73 of the line to be continued and an ampersand in position 6 of the continuing line.

Related Topics:

INCLUDE line

To Read More About It:

ISO 1539 : 1991, Fortran Standard, 3.3
Fortran 90 Handbook, 3.3, 3.4
Programmer's Guide to Fortran 90, 1.4

Things To Know:

  1. A Fortran program consists of a sequence of statements; they are written on lines that contain from 0 to 132 characters.
  2. A statement can be continued onto more lines if the last character of the line (not in a comment) to be continued is an ampersand (&). 
    PRINT *,  &
      "I hope this is the right answer."
    An ampersand must be used on the continuing line if a keyword or character string is split between lines in free source form. A statement may not have more than 40 lines.
  3. The semicolon (;) symbol is used to separate multiple statements on the same line; it may be used in both free and fixed source form programs. 
    A = 0; B = 0
  4. The ! symbol for a comment may be used in both free and fixed source form programs.
  5. In the absence of a continuation symbol, the end of a line marks the end of a statement.
  6. Blank characters are significant in a Fortran program written using free source form. In general, they must not occur within things that normally would not be typed with blanks in English text, such as names and numbers. On the other hand, they must be used between two things that look like ``words''. An example is that in the first line of a program the keyword PROGRAM and the name of the program must be separated by one or more blanks, as in the example PROGRAM ADD_2.
  7. Keywords and names such as PRINT and NUMBER must contain no blank characters, except that keywords that consist of more than one English word may contain blanks between the words, as in the Fortran statement END DO. Two or more consecutive blanks are always equivalent to one blank unless they are in a character string.
  8. Any occurrence of the exclamation symbol (!) other than within a character context or a comment marks the beginning of a comment. The comment is terminated by the end of the line. All comments are ignored by the Fortran system.
  9. Statements may begin anywhere, including positions 1 to\x116.
  10. Labels may appear anywhere before the main part of the statement, even in a position to the right of position\x116.
  11. A construct name followed by a colon may appear anywhere before the main part of the statement.