I've made an infinite loop and can't seem to figure out what I did wrong

zeewhiz 0
Viewed 29

I'm writing a program for a simple game of Odds and Evens, but I can't seem to figure out what's wrong with my while loop.

Game rules: https://en.wikipedia.org/wiki/Odds_and_evens_(hand_game)

It's meant to make it so that while the user doesn't enter either odds, Odds, evens, or Evens an alert comes up saying 'Please enter either odds or evens'.

But, whenever I run the code, it just turns into an infinite loop, repeating the alert, no matter what I put in. Even if it is the correct response I want.

var oddEven = prompt('Would you like to be odds or evens?', 'Odds') 
while (oddEven != 'odds' || oddEven != 'Odds' || oddEven != 'evens' || oddEven != 'Evens') {
    oddEven = prompt('Please enter either odds or evens');
}

I am very new to programming and just started learning a couple months ago so any advice would be appreciated.

Thanks for the help :)

while-loop prompt javascript
2 Answers

Imagine a user gives the input "Odds", what happens in your if statement?

oddEven != 'odds' is false, but we still need to check the others! We need to check the others because you have written || which means "or" - javascript will keep going through each statement until one of them is true.

oddEven != 'Odds' is true. Because it is true, your while-loop immediately continues, again because you have used || - if ANY of the statements is true the code will stop checking statements and continue the loop.

There are lots of ways to fix this but I think the following is best for comparing to how you got stuck:

var oddEven = prompt('Would you like to be odds or evens?', 'Odds') 
while (
    !(oddEven == 'odds' || oddEven == 'Odds' || oddEven == 'evens' || oddEven == 'Evens')
) {
    oddEven = prompt('Please enter either odds or evens');
}

Now in our example, oddEven == 'Odds' is true, but because the whole section is negated by the bang ! at the start, we're taking the opposite of that, so false.

A tidier way of doing this could be as follows:

var oddEven = prompt('Would you like to be odds or evens?', 'Odds') 
while (!['odds', 'Odds', 'evens', 'Evens'].includes(oddEven)) {
    oddEven = prompt('Please enter either odds or evens');
}

This says "while this list of inputs does not include oddEven".

LaytonGB0

So it's an Or, any condition that satisfies even one, will evaluate to true. So if I enter 'boo', oddEven != 'boo', and therefore the rest evaluates as true. A better way would be

while (oddEven in ['odds', 'Odds' ...]): 
    oddEven = prompt('Please enter either odds or evens')
Eric Yang0
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