public static void main(String[] args) {
        evalRPN evalRPN = new evalRPN();

        String[] testA = {"2", "1", "+", "3", "*"};
        String[] testB = {"4", "13", "5", "/", "+"};

        System.out.println(evalRPN.evalRPN(testA));
        System.out.println(evalRPN.evalRPN(testB));
        System.out.println(evalRPN.isOperator("+"));
        System.out.println(evalRPN.isOperator("ss"));

    }