Question

Getting a 102 runtime error on the pascal program.  Any ideas of why?

Program test (Output, DataIn, DataOut);

var
  Num : Integer;
  DataIn, DataOut : Text;
  
begin
  Reset(DataIn);
  Rewrite(DataOut);
  Read(DataIn, Num);
  Writeln(DataOut, Num);
end.

https://onlinegdb.com/mcSfBaXd8

Answer 1

You have not assigned the text files DataIn and DataOut to their file names. Use

Assign(DataIn, 'myFile.dat');

Also, the link you provided does not work. Click on the SHARE button (3 to the right of the RUN button) and use the link there to share your project.

Read this article on file handling: 

Comments

It is worth noting this is a Delphi (and FreePascal) peculiarity. Technically speaking Gary’s program is correct and complies with ISO standard 7185 (and 10206).  The GNU Pascal Compiler will successfully compile this program and it is usable.

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That's a useful information. I only had experience with Turbo Pascal (about 20 years ago, Jeese, I'm old) as a student.

Thank you for the details!

Answer 2

Thank you very much. The Weems/Dale Pascal text book I was using uses the ISO standard of Pascal. It does not define the nonstandard procedure 'Assign'. However, their other book "Turbo Pascal" does.

Comments

If I'm not mistaken, OnlineGDB runs Turbo Pascal, so that's why you definitely need Assign for this online compiler.

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Turbo Pascal seems to be the popular version of Pascal. Thanks for your comment regarding Assign. It fixed my problem of reading and writing to external files.