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.)