2

Due to some restriction on my assignment, F77 is used. I am learning to use subroutine but I encounter error when trying to write string out.

  PROGRAM test
  IMPLICIT NONE
  INTEGER a
  CHARACTER*20 STR,str1
  STR = 'Hello world'
  a = 1     
  WRITE (*,*) a  
  WRITE (*,10) STR    
  CALL TEST(str1)
  STOP
  END

  SUBROUTINE test(str2)
  CHARACTER*20 str2
  str2 = 'testing'
  WRITE (*,10) STR2
  RETURN
  END

When trying to compile this code, it returns that 'Error: missing statement number 10'

Also, I have some other questions:

  1. What does the *20 mean in CHARACTER*20 STR? Is this the size of the string?

  2. How about 10 in WRITE (*,10) STR? Is this the length of string to be written?

  3. what does (*,*) mean in WRITE (*,*) a

francescalus
  • 30,576
  • 16
  • 61
  • 96
Kent Wong
  • 143
  • 8
  • Please use tag [tag:fortran] for all Fortran questions. – Vladimir F Героям слава Feb 02 '19 at 19:01
  • 2
    Your questions are really about basic syntax of the language and you could fin better answers in your favorite Fortran book or tutorial out there; thus I am considering it off-topic here. I will let you some references so you can read and learn: 1. [character syntax](https://stackoverflow.com/questions/33415590), 2. [format label](https://stackoverflow.com/questions/29868607) and [statement](https://web.stanford.edu/class/me200c/tutorial_77/17_format.html), 3. [write syntax](https://docs.oracle.com/cd/E19957-01/805-4939/6j4m0vnbs/index.html) – Rodrigo Rodrigues Feb 02 '19 at 23:13
  • 1
    Also in feedback to your tutor please say that Fortran77 shouldn't have been taught for the last 20 years and is an inappropriate tool for students in this age who should at the very, very least being taught Fortran95, better Fortran2003 – Ian Bush Feb 03 '19 at 07:53

2 Answers2

3

As you can read for example here: https://www.obliquity.com/computer/fortran/io.html

the second value given to write is an argument for the implicit format keyword, which is the label of a statement within the same program unit, a character expression or array containing the complete format specification, or an asterisk * for list-directed formatting.

Thus if you provide the data directly, you may want to use * there instead. Otherwise, your program needs to have the label 10 at some line with formatting statement.

And yes, CHARACTER*20 STR means that the variable STR is of length 20, as you can read for instance here: https://www.obliquity.com/computer/fortran/datatype.html

Palo
  • 974
  • 12
  • 27
2

The *20 after CHARACTER specifies the size of the CHARACTER variable (in this case 20 characters). FORTRAN doesn't use null-terminated strings like other languages, instead you have to reserve a specific number of characters. Your actual string can be shorter than the variable, but never longer.

The comma ( , ) in the write statement is used to separate the various arguments. Some versions of FORTRAN allow you to supply 'named' arguments but the default is the first argument is the file code to write to (a '*' implies the standard output). The second argument would be the line number of a FORMAT statement. There can be more arguments, you'd have to look up the specifics for the OPEN statement in your version of FORTRAN.

Some of your WRITE() statements are specifying to use the FORMAT statement found at lable '10'. But your sample doesn't provide any FORMAT statement, so this would be an error.

If you don't want to deal with a FORMAT statement, you can use an asterisk ( * ) as the second argument and then FORTRAN will use a general default format. That is what your first WRITE(,) is doing. It writes to 'stdout' using a general format.

Mike F
  • 21
  • 1
  • 2