A-M baby

Task/Loops-Continue/Fortran/loops-continue-2.f

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+C     WARNING: This program is not valid ANSI FORTRAN 77 code. It uses
+C     one nonstandard character on the line labelled 5001. Many F77
+C     compilers should be okay with it, but it is *not* standard.
+C
+C     It is also worth noting that FORTRAN 77 uses the command CONTINUE,
+C     but not in the semantic, looping sense of the word. In FORTRAN,
+C     CONTINUE means "do absolutely nothing." It is a placeholder. If
+C     anything, it means "continue to the next line."
+C
+C     Python does the same thing with `pass`; C and its family of
+C     languages, with `{/* do nothing */}`. Write CONTINUE when you need
+C     to write something but have nothing to write.
+C
+C     This page on Rosetta Code is about a very different "continue"
+C     statement that tells a loop to go back to the beginning. In
+C     FORTRAN, we use (you guessed it!) a GOTO to accomplish this.
+      PROGRAM CONTINUELOOP
+        INTEGER I
+
+        DO 10 I = 1, 10
+C         Is it five or ten?
+          IF (MOD(I, 5) .EQ. 0) THEN
+C           If it is, write a newline and no comma.
+            WRITE (*,5000) I
+
+C           Continue the loop; that is, skip to the end of the loop.
+            GOTO 10
+          ENDIF
+
+C         Write I with a comma and no newline.
+          WRITE (*,5001) I
+
+C       Again, in this case, CONTINUE is completely unrelated to the
+C       semantic, looping sense of the word.
+   10   CONTINUE
+
+        STOP
+
+C       This will print an integer and a newline (no comma).
+ 5000   FORMAT (I3)
+
+C       Standard FORTRAN 77 is completely incapable of completing a
+C       WRITE statement without printing a newline. If you want to print
+C       five integers in standard code, you have to do something like
+C       this:
+C
+C           FORMAT (I3, ',', I3, ',', I3, ',', I3, ',', I3)
+C
+C       Writing `1, 2, 3, 4, 5` and then `6, 7, 8, 9, 10` to that format
+C       would produce the following two lines:
+C
+C             1,  2,  3,  4,  5
+C             6,  7,  8,  9, 10
+C
+C       However, this code exists to demonstrate continuing a FORTRAN 77
+C       loop and not to demonstrate how to get around its rigidity about
+C       newlines.
+C
+C       The dollar sign at the end of the format is a nonstandard
+C       character. It tells the compiler not to print a newline. If you
+C       are actually using FORTRAN 77, you should figure out what your
+C       particular compiler accepts. If you are actually using Fortran
+C       90 or later, you should replace this line with the commented
+C       line that follows it.
+ 5001   FORMAT (I3, ',', $)
+C5001   FORMAT (I3, ',', ADVANCE='NO')
+      END