How Loop Through Again If User Inputs Wrong Word

Question

Basically, what I want my code to do is if the user inputs anything besides "sum, quit, max, min" I want the program to loop back and ask the user the options again. I tried using a while-loop but I can't add multiple String objects within it. I'm stuck on what to do. (Also, I used if-statements instead of while so it won't continually repeat and be stuck.)

EDIT: thank you for the help! I used a while(true), break statements, and a continue at the end and it seems to work!

public static void main (String [] args){
        System.out.println("Enter the option sum, max, min:");
        Scanner input = new Scanner (System.in);
        user = input.nextLine();
        double [] y = theArray();


        if (user.equals("sum")){
            //do something

        }
        else if (user.equals("max")){
            //do something 
        }
        else if (user.equals("min")){
            //do something
        }
        else if (user.equals("Quit")){
            //do something
        }


    }
}

What do you mean by "I can't add multiple String objects within it"? — Cardinal System, Oct 26 '17 at 21:24
within a while loop you cant say while(user.equals("quit", "sum"); — csstudent2x, Oct 26 '17 at 21:27
Use the `while` infinite loop and break it when the condition is met. — Nikolas Charalambidis, Oct 26 '17 at 21:27
@csstudent2x oh, I get it. I didn't understand that's what he meant. — Cardinal System, Oct 26 '17 at 21:28
Just a comment on your note with the while statement; although you can't say `while(user.equals("quit", "sum")){` you *can* say `while(user.equals("quit") || user.equals("sum")){` , and add more `||`'s (Or's) as needed for anything else. If that logic makes more sense to you than the break or the recursion answers below, give it a try. — Davy M, Oct 26 '17 at 21:41

score 1 · Answer 1 · answered Oct 26 '17 at 21:34

As I have said in the comment above, use the while infinite loop and break it when the condition is met. If the condition is not met, the loop goes for the next iteration. Keep aware what should be looped and why.

System.out.println("Enter the option sum, max, min:");
Scanner scanner = new Scanner(System.in);
String option;

while (scanner.hasNextLine()) {
    System.out.println("Enter the option sum, max, min:");
    option = scanner.nextLine();
    if ("sum".equals(option)) {
        System.out.println("Sum entered, loop ended");
        // do something
        break;
    } else if ("max".equals(option)) { // the same goes for min, max, quit }
}

score 0 · Answer 2 · answered Oct 26 '17 at 21:36

I would suggest using recursion:

public static void main (String [] args){

        Scanner input = new Scanner (System.in);

        promptUser(input);

        System.out.println("done");

    }
    public static void promptUser(Scanner input) {
        System.out.println("Enter the option sum, max, min:");
        String user = input.nextLine();
        double [] y = theArray();


        if (user.equals("sum")){
            //do something
        }
        else if (user.equals("max")){
            //do something
        }
        else if (user.equals("min")){
            //do something
        }
        else if (user.equals("Quit")){
            //do something
        }else {
            //if wrong input is entered, try again
            promptUser(input);
        }
    }

Any idea if Java would optimize this into a tail recursive form? — MFisherKDX, Oct 26 '17 at 21:38

How Loop Through Again If User Inputs Wrong Word

2 Answers2