8.5.2 Statements, Comments, and Lines

(Corresponds to Section 2.3 of ANSI X3.9-1978 FORTRAN 77.)

Use of an exclamation point (`!') to begin a trailing comment (a comment that extends to the end of the same source line) is permitted under the following conditions:

• The exclamation point does not appear in column 6. Otherwise, it is treated as an indicator of a continuation line.
• The exclamation point appears outside a character or Hollerith constant. Otherwise, the exclamation point is considered part of the constant.
• The exclamation point appears to the left of any other possible trailing comment. That is, a trailing comment may contain exclamation points in their commentary text.

Use of a semicolon (`;') as a statement separator is permitted under the following conditions:

• The semicolon appears outside a character or Hollerith constant. Otherwise, the semicolon is considered part of the constant.
• The semicolon appears to the left of a trailing comment. Otherwise, the semicolon is considered part of that comment.
• Neither a logical IF statement nor a non-construct WHERE statement (a Fortran 90 feature) may be followed (in the same, possibly continued, line) by a semicolon used as a statement separator.

  This restriction avoids the confusion that can result when reading a line such as:

            IF (VALIDP) CALL FOO; CALL BAR
       

  Some readers might think the `CALL BAR' is executed only if `VALIDP' is .TRUE., while others might assume its execution is unconditional.

  (At present, g77 does not diagnose code that violates this restriction.)