import java.util.Scanner;


public class Calculator{

    private static final String SUMMAA = "add";
    private static final String EROTA = "diff";
    private static final String KERRO = "multi";
    private static final String JAA = "div";
    private static final String LOPETA = "quit";

    public static String[] tarkista(String userInput) {
        String[] array = userInput.split(" ");
        System.out.println(array);
        if (array == null || array[0] != SUMMAA || array[0] != EROTA || array[0] != KERRO ||
        array[0] != JAA){
            return null;
        } else {
            return array;
        }
    }
    public static void main(String[] args){
        Scanner reader = new Scanner(System.in);
        System.out.println("Hello! I am a simple calculator.");
        boolean asking = true;
        while (asking == true){
            System.out.println("Please, enter a command:");
            String input = reader.nextLine();

            if (input == LOPETA){
                asking = false;
            } else {
                String[] operation = tarkista(input);
                System.out.println(operation);
                if (operation == null){
                    System.out.println("Error!");
                } else {
                    int num1 = Integer.parseInt(operation[1]);
                    int num2 = Integer.parseInt(operation[2]);
                    if (operation[0] == SUMMAA) {
                        System.out.println(num1 + num2);
                    }
                    if (operation[0] == EROTA) {
                        System.out.println(num1 - num2);
                    }
                    if (operation[0] == KERRO) {
                        System.out.println(num1 * num2);
                    }
                    if (operation[0] == JAA) {
                        System.out.println(num1 / num2);
                    }
                }
            }
        }
    }
}