$include "seed7_05.s7i";

const func string: middle3 (in integer: number) is func
  result
    var string: middle3 is "";
  begin
    middle3 := str(abs(number));
    if not odd(length(middle3)) or length(middle3) < 3 then
      middle3 := "error";
    else
      middle3 := middle3[succ((length(middle3) - 3) div 2) len 3];
    end if;
  end func;

const proc: main is func
  local
    var integer: number is 0;
    var string: mid3 is "";
  begin
    for number range [] (123, 12345, 1234567, 987654321, 10001, -10001, -123,
                         -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0) do
      writeln(number <& ": " <& middle3(number));
    end for;
  end func;