import java.util.InputMismatchException;
import java.util.Scanner;
import java.util.Objects;

public class Calculator {

    public static void main(String[] args) {

        try {
            while (true) {
                int number1, number2;
                int result = 0;
                String operator;

                System.out.println("Operations are: “add”, “sub”, “mul”, “div”");
                System.out.println("Enter first number:");
                Scanner scanner = new Scanner(System.in);

                if (scanner.hasNextInt()) {
                    number1 = scanner.nextInt();

                    System.out.println("Enter second number:");
                    number2 = scanner.nextInt();

                    System.out.println("Enter an operation:");
                    operator = scanner.next();

                    switch (operator) {
                        case "add":
                            result = number1 + number2;
                            break;

                        case "sub":
                            result = number1 - number2;
                            break;

                        case "mul":
                            result = number1 * number2;
                            break;

                        case "div":
                            result = number1 / number2;
                            break;

                        default:
                            System.out.println("wrong input");
                            break;
                    }
                    System.out.println("Result: " + result);
                } else if (Objects.equals(scanner.next(), "q")) {
                    break;
                } else {
                    System.out.println("You're input is invalid. Chose a number.");
                }
            }

        } catch (InputMismatchException e) {
            System.err.println(e);
        }
    }
}