Thread: while loop loops foreve even with the right inputs.

Could anyone point me to why when the user enters Y or N, this loop still continues looping instead of quitting?

Thanks

                         System.out.println("Enter Y to indicate  Up OR N to indicate Down " + "\n");			
			String option = scanner.nextLine();
 
			while (!response.equalsIgnoreCase("Y")||(!response.equalsIgnoreCase("N"))) {
				System.out.println("Enter Y to indicate  Up OR N to indicate Down " + "\n");			
			        option = scanner.nextLine();
				}

Hi PhHein,

I see the logic in it but how could I write it such that only when the user enter's Y or N will the loop stop because based on whether the user enter's Y or N, the programme goes into the next state. So, it is expedient the user enter's one of these options. Anyway, one could still do this and not fall into this logical trap?

how could I write it such that only when the user enter's Y or N will the loop stop because based on whether the user enter's Y or N

Whoa! Slow down. Make sense. Communicate clearly. It's not clear you understand the requirement, and if you don't understand it or can't communicate it clearly, then we can't help you.

Sorry Greg IF I didn't make sense. Here is what I want to make sense of: I want the user to either choose Y or N for the loop to quite. Should the user enter any other character aside these two, the loop continues. Only when the user enters Y for yes and N for no, should the loop quite. Does that make sense now?

Here's how I read your explanation:

User enters:

'Y' = loop quits (exits)
'N' = loop quits (exits)
Any character other than 'Y' or 'N' = loop continues

Is that what you meant?

Yes sir. That is what I am looking for.

What was the wrong with PhHein's suggestion to use && instead of ||? Did you try that?

Edit: And why not use 'U' for Up and 'D' for down (or similar)? The Y/N logic to indicate the user's desired state is confusing to the programmer and makes little sense to the user.

Well, here is his code:

String option = "";
do{
option = ......
} while (!option.equals(whatever));

I didn't quite make much sense out of it. I did ask if he could elaborate more on it. I understood his idea that you can't use the !option.equalsIgnore("Y") when it is N or Y when it is N. What I don't understand is how his do-while loop solves that.

His response had 2 suggestions, not necessarily meant to be taken together:

Suggestion 1: Change || to &&

Suggestion 2: Change the design from a while to a do/while

His Suggestion 2 indicated the more common approach to what you're trying to do based on the general rule for which loop to choose: If the loop is driven by a known number of occurrences: use for(): if the number of desired loops is unknown, use while(); if the number of desired loops is unknown but at least one execution is required, use do/while(). HOWEVER, any can be used.

Try his first suggestion and see what happens.

Hi, Greg,

I solved it now. I just had to think about it differently because I didn't understand his approach. Thanks anyways for the response.