CODEWITHSUNDEEP
javascriptwhile-loop
T_Turner
T_Turner

Reputation: 129

multiple conditions within a while loop - Javascript

I want to prompt the user for an input and if it isn't a valid option reprompt until a valid input is entered.

Right now it always reprompts not matter the input, correct or not.

Here is the code:

var userChoice = prompt("Do you choose rock, paper, scissors or rope?");
while (userChoice != "rock" || "paper" || "scissors" || "rope") {
    userChoice = prompt("Sorry invalid input, please enter either: rock, paper,scissors, or rope.");
}

Seems like it should be a simple thing to do, am I misunderstanding how to use while loops? maybe the operators are wrong? haven't been able to find anything useful, any help is appreciated!

Upvotes: 2

Views: 24248

Answers (6)

ruslaniv
ruslaniv

Reputation: 604

I'll try a more generic answer:

The while loop runs while whatever in the brackets is TRUE.

The way || works, it will evaluate to TRUE if at least one of the operands is TRUE.

So in your case even if you select

userChoice = "rock";
userChoice != "rock" => FALSE

whatever comes after || will still evaluate to TRUE because

"rock" != "paper" => TRUE

and thus your whole condition in the brackets will evaluate to TRUE.

So in order to break out of the loop, you need to have the condition in the brackets evaluate to FALSE.

The way && works, it will evaluate to FALSE if at least one of the operands evaluates to FALSE.

And since 

userChoice = "rock";
userChoice != "rock" => FALSE

the loop does not even check the rest of the conditions you might have and breaks out of the loop.

Upvotes: 0

Aprillion
Aprillion

Reputation: 22322

for more complicated rules (such as ignoring case sensitivity), it is possible to use regular expressions, e.g. match:

while( ! userChoice.match(/^\s*(?:rock|paper|scissors|rope)\s*$/i)) { ... }

(see explanation of the regex on https://regex101.com/r/sV3tJ1/1#javascript)

note: thanks Willem Van Onsem for suggesting regex

also avaliable are object literals:

var validChoices = {rock: true,
                    paper: true,
                    scissors: true,
                    rope: true},
    userChoice = ...
while ( ! validChoices.hasOwnProperty(userChoice)) {
  ...
}

or ES6 Set for the newest browsers as of 2016: new Set(["rock", "paper", ...])

Upvotes: 2

smcd
smcd

Reputation: 3265

You could also use an array and indexOf

var userChoice = prompt("rock, paper, scissors, rope?").toLowerCase();
while (["rock", "paper", "scissors", "rope"].indexOf(userChoice) === -1) {
    userChoice = prompt("Please choose: rock, paper, scissors, rope?").toLowerCase();
}

alert("You chose '" + userChoice + "'");

Upvotes: 5

Nina Scholz
Nina Scholz

Reputation: 386654

Maybe an array is smarter to use with Array.prototype.indexOf().

var userChoice;
while (!~["rock", "paper", "scissors", "rope"].indexOf(userChoice)) {
    userChoice = prompt("Sorry invalid input, please enter either: rock, paper,scissors, or rope.");
}

Upvotes: 2

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 476719

The syntax "rock" || "paper" is valid, but the OR will bind later than the equality check, so basically you write:

while ((userChoice != "rock") || "paper" || "scissors" || "rope") {
    //...
}

Now since you use such or's, you basically do an effectiveness check and at least "paper" is effective. You can however get the behavior you aim, by using explicit checks and using the && operator instead of the ||:

while (userChoice !== "rock" && userChoice !== "paper" && userChoice !== "scissors" && userChoice !== "rope") {
    //...
}

Upvotes: 4

Hogan
Hogan

Reputation: 70523

While userChoice does not equal any of the choices... so AND

while (userChoice != "rock" && userChoice != "paper" && userChoice != "scissors" && userChoice != "rope") {

Upvotes: 2

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