g77.info: Exclamation Point

Meaning of Exclamation Point in Column 6

   `g77' treats an exclamation point (`!') in column 6 of a fixed-form
source file as a continuation character rather than as the beginning of
a comment (as it does in any other column) when the `-fvxt' option is
specified.

   The following program, when run, prints a message indicating whether
it is interpreted according to GNU Fortran (and Fortran 90) rules or
VXT Fortran rules:

     C234567  (This line begins in column 1.)
           I = 0
          !1
           IF (I.EQ.0) PRINT *, ' I am a VXT Fortran program'
           IF (I.EQ.1) PRINT *, ' I am a Fortran 90 program'
           IF (I.LT.0 .OR. I.GT.1) PRINT *, ' I am a HAL 9000 computer'
           END

   (In the GNU Fortran and Fortran 90 languages, exclamation point is a
valid character and, unlike space (<SPC>) or zero (`0'), marks a line
as a continuation line when it appears in column 6.)