}else {
            System.out.println("Entered to the calculation zone"); // message
            int operatorIndex = 'N';
            char operator;
            for (int i=0; i<expr.length(); i++) {
                //check the operator
                operator = expr.charAt(i);

                if (expr.charAt(i) == '+' || expr.charAt(i) == '-') {
                    System.out.println("plus and minus zone");
                    operatorIndex = i;
                    System.out.println(operatorIndex);
                } else if (expr.charAt(i) == '*' || expr.charAt(i) == '/') {

                       // TODO: 5/22/2019  function for kefet and hiluk
                       // return eval("lol from left") * eval("lol from right");

                }

            }
            String leftExpr, rightExpr;
            rightExpr = expr.substring(operatorIndex + 1);
            leftExpr = expr.substring(0,operatorIndex);
            System.out.println("Right Expression is " + rightExpr);
            System.out.println("Left Expression is " + leftExpr);

            switch (expr.charAt(operatorIndex)){
                case '+':
                    System.out.println("PLUS");
                    return eval(leftExpr) + eval(rightExpr);

                case '-':
                    System.out.println("MINUS");
                    return eval(leftExpr) - eval(rightExpr);

                default:
                    throw new IllegalStateException("Unexpected value: " + expr.charAt(operatorIndex));
            }


        }


    }