(* File: palindrome.griffin
 * Determines if a string is a palindrome.
 * (C) 2014 Ariel Ortiz, ITESM CEM
 *)

var
    str, option: string;

procedure IsPalindrome(
    str: string; 
    ): boolean;
    var
        start, finish: integer;
    begin
        start := 0;
        finish := LenStr(str) - 1;

        loop
            if start > finish then exit; end;
            if CmpStr(AtStr(str, start), AtStr(str, finish)) <> 0 then
                return false;
            end;
            start := start + 1;
            finish := finish - 1;
        end;

        return true;
    end;

program

    loop
        WrStr("Input a string: ");
        str := RdStr();

        if IsPalindrome(str) then
            WrStr(CatStr("The string """, CatStr(str, """ is a palindrome.")));
        else
            WrStr(CatStr("The string """, CatStr(str, """ is NOT a palindrome.")));
        end;

        WrLn();

        WrStr("Check another string? ");
        option := RdStr();

        if LenStr(option) = 0 then
            option := "N";
        else
            option := AtStr(option, 0);
        end;

        if CmpStr(option, "Y") <> 0 and CmpStr(option, "y") <> 0 then
            exit;
        end;
    end;

end;