$ include "seed7_05.s7i";

const func string: rot (in string: stri, in integer: encodingKey) is func
  result
    var string: encodedStri is "";
  local
    var char: ch is ' ';
    var integer: index is 0;
  begin
    encodedStri := stri;
    for ch key index range stri do
      if ch >= 'a' and ch <= 'z' then
        ch := chr((ord(ch) - ord('a') + encodingKey) rem 26 + ord('a'));
      elsif ch >= 'A' and ch <= 'Z' then
        ch := chr((ord(ch) - ord('A') + encodingKey) rem 26 + ord('A'));
      end if;
      encodedStri @:= [index] ch;
    end for;
  end func;

const proc: main is func
  local
    const integer: exampleKey is 3;
    const string: testText is "The five boxing wizards jump quickly";
  begin
    writeln("Original:  " <& testText);
    writeln("Encrypted: " <& rot(testText, exampleKey));
    writeln("Decrypted: " <& rot(rot(testText, exampleKey), 26 - exampleKey));
  end func;