如果用户输入了无效密码，该如何编码？

Question

If the user enters an invalid code, display You selected an invalid option and set the price to 0.

import java.util.Scanner;
public class ShadyRestRoom {

    public static void main(String[]args) {
        Scanner scanner= new Scanner(System.in); 
        int QueenBed = 125;
        int KingBed = 139;
        int KingPullout = 165;

         System.out.println("Choose: 1 for a Queen bed Choose: 2 for a King bed or Choose: 3 for a King bed with a pullout couch");
         int RoomChoice= scanner.nextInt();

         if (RoomChoice == 1) 
             System.out.println("$125 for a Queen bed");
         if (RoomChoice == 2)
             System.out.println("$139 for a King bed");
         if (RoomChoice == 3)
             System.out.println("$165 for a King bed with a pullout couch");

         while (RoomChoice == 4) 
             System.out.println("ERROR Please enter a valid Choice");
             RoomChoice = scanner.nextInt();
         if (RoomChoice == 8)
             System.out.println("ERROR Please enter a valid Choice");
             RoomChoice = scanner.nextInt();    
    }
}

I can't seem to figure out how to set it so it does= ( If the user enters an invalid code, display You selected an invalid option and set the price to 0.)

Answer 1

One way do accomplish a choice is a switch statement. It is made for it. So a choice calls for a switch.

Now in a switch you have for every valid choice one "case" statement. Additionally in the end there is a "default" for everything else not mentioned explicitely.

You can use that default to "cheat" and reset a variable to a defined value, of your choice.

Now that again makes the condition in the loop simpler as it isn't so vague("some input except..") anymore but there is only one defined value that says "another loop".

I took "-1" as an indicator, that says "something went wrong". But you can use whatever makes sence to you as "escape"(thats what such values are called: -1 is an "escape code"). And so the while checks for my escape "-1" and continues asking until the user gives something in range.

public static class ShadyRestRoom {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int QueenBed = 125;
        int KingBed = 139;
        int KingPullout = 165;
        int RoomChoice = -1;
        do { 
            System.out.println("Choose: 1 for a Queen bed Choose: 2 for a King bed or Choose: 3 for a King bed with a pullout couch");
            RoomChoice = scanner.nextInt();
            switch (RoomChoice) {
                case 1:
                    System.out.println("$125 for a Queen bed");
                    break;
                case 2:
                    System.out.println("$139 for a King bed");
                    break;
                case 3:
                    System.out.println("$165 for a King bed with a pullout couch");
                    break;
                //you can also explicitely take a group of numbers that need to be treated the same way:
                case 4:
                case 8:
                default:    //this is the default for everything that wasn't metioned before
                    RoomChoice = -1;
                    System.out.println("ERROR Please enter a valid Choice");
            }
        } while (-1 == RoomChoice);

    }
}

Btw: it is a convention to use lower case letters for variables. So "roomChoice" instead of "RoomChoice" would be better. With that you could see immediately that is a variable and not class.