rot13.pas

program rot13;

{
Byte     = 1 byte
ShortInt = 2 bytes
Integer  = 4 bytes
}

function rot13(x : char): char;
var
   ans   : ShortInt;
   shift : ShortInt;
begin
   rot13 := x;

   shift := 0;
   if ('a' <= x) and (x <= 'z') then shift := ord('a');
   if ('A' <= x) and (x <= 'Z') then shift := ord('A');

   if shift > 0 then
   begin
      ans   := ord(x);         {convert to ASCII code}
      ans   := ans - shift;    {conver to number in the alphabet}
      ans   := ans + 13;       {shift by 13 to the right}
      ans   := ans mod 26;     {wrap around the alphabet}
      ans   := ans + shift;    {convert back to ASCII code}
      rot13 := chr(ans);       {convert back to char}
   end;
end;

var
   chunk : String[512];
   i     : Integer;
   n     : Integer;
begin
   n := 0;
   repeat
      { TODO: the program probably does not work correctly with new lines}
      read(chunk);
      for i := 1 to length(chunk) do
      begin
         write(rot13(chunk[i]))
      end;
      inc(n);
   until length(chunk) = 0;
   writeln;
   writeln('Read ', n, ' chunks');
end.