{ t55_strcat_overflow: concatenating past the maximum is a RUNTIME error.

  A `string' is string[255] - a length byte and 255 characters - so the scratch
  a concatenation writes into cannot hold more than 255.  Reading 128
  characters and then doing `s := s + s' asks for 256.  TP3's xconcat raises
  "string too long" (error 16) instead of truncating, and this runtime leaves
  through INT 21h AH=4Ch with AL=16.

  `after' must NOT appear: the error path leaves the program, it does not set a
  flag, truncate, and carry on.  The .out pins where it stopped and the .exit
  file pins WHY - exit 16, not the 0 progend would give. }
program t55_strcat_overflow (input, output);
var
   s : string;
begin
   readln (s);
   writeln ('read');
   s := s + s;
   writeln ('after')
end.