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Edit summary for version 31 :
New Pascal implementation by user [Slce]

Version 30

Version 31

Idiom #59 Write to standard error stream

Print the message "x is negative" to standard error (stderr), with integer x value substitution (e.g. "-2 is negative").

Idiom #59 Write to standard error stream

Print the message "x is negative" to standard error (stderr), with integer x value substitution (e.g. "-2 is negative").

Code
writeln(StdErr , x , ' is negative');
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If first argument indicates a text file or stream (as here), it is taken as the output file for writeln.
Doc URL
https://www.freepascal.org/docs-html/rtl/system/writeln.html
Demo URL
http://tpcg.io/nshNmK