javascript - Switch() does not work with Math.random() numbers - Stack Overflow

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I am trying to make a function that involves switch() and gives me answers on specific, randomly generated numbers. Somehow my function does not run the case it is supposed to run. It only gives me the default case, no matter what the number is.

This is my code:

var i;
var girl;

function response() {
    var girl = prompt("What girl do you like?");
    var r = (Math.random() * (3 - 1 + 1) + 1).toFixed(0);
    var i = r;

    switch(i) {
        case (i == 1):
            alert(girl + " likes you as a friend.");
            break;

        case (i == 2):
            alert(girl + " does not really like you.");
            break;

        case (i == 3):
            alert(girl + " has a crush on you.");
            break;

        case (i == 4):
            alert(girl + " wants you to ask her out.");
            break;

        default:
            console.log(i);
    }
}

I am trying to make a function that involves switch() and gives me answers on specific, randomly generated numbers. Somehow my function does not run the case it is supposed to run. It only gives me the default case, no matter what the number is.

This is my code:

var i;
var girl;

function response() {
    var girl = prompt("What girl do you like?");
    var r = (Math.random() * (3 - 1 + 1) + 1).toFixed(0);
    var i = r;

    switch(i) {
        case (i == 1):
            alert(girl + " likes you as a friend.");
            break;

        case (i == 2):
            alert(girl + " does not really like you.");
            break;

        case (i == 3):
            alert(girl + " has a crush on you.");
            break;

        case (i == 4):
            alert(girl + " wants you to ask her out.");
            break;

        default:
            console.log(i);
    }
}

• javascript
• switch-statement

Share Improve this question Follow edited Sep 30, 2016 at 9:13 alex 491k204204 gold badges889889 silver badges991991 bronze badges asked Sep 30, 2016 at 9:02 VincentVincent 16733 silver badges1616 bronze badges 1

• toFixed converts to a string, so you might want to use case '1':, case '2':, etc. Also, your range won't cover all cases, you might want to use var i = (Math.random() * 4 + 1).toFixed(0);. – Yimin Rong Commented Sep 30, 2016 at 9:07

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4 Answers 4

Sorted by: Reset to default 5

That's not how a switch works. It pares the value for each case to the switch.

Essentially now, it is paring the value of i multiple times to boolean values (the result of, for example i == 1).

Also, your randomness doesn't bee more random by adding arithmetic with static values into the value like you did. You should replace it with 4. You also should use something like Math.ceil() (since you're ignoring the 0 value, which is also probably not a good idea), not toFixed() which returns a string.

You also don't need the parenthesis around the values to pare. If you know the range of the random number, you also probably don't need a default case (since you cover every possibility already).

You can also use r directly, no need to reassign it.

Your variables are also local to your function, so probably don't need them at the top.

Here is how I would re-write this:

function response() {
    var girl = prompt("What girl do you like?");
    var r = Math.floor(Math.random() * 4);

    switch(r) {
        case 0:
            alert(girl + " likes you as a friend.");
            break;

        case 1:
            alert(girl + " does not really like you.");
            break;

        case 2:
            alert(girl + " has a crush on you.");
            break;

        case 3:
            alert(girl + " wants you to ask her out.");
            break;

    }
}

...or even...

function response() {
    var answerSuffixes = [
        " likes you as a friend.",
        " does not really like you.",
        " has a crush on you.",
        " wants you to ask her out."
    ];
    var girl = prompt("What girl do you like?");
    var r = Math.floor(Math.random() * answerSuffixes.length);

    alert(girl + answerSuffixes[r]);
}

The case statement in Javascript already does a match on the target i:

switch(i) {
        case 1:
            alert(girl + " likes you as a friend.");
            break;

        case 2:
            alert(girl + " does not really like you.");
            break;

        case 3:
            alert(girl + " has a crush on you.");
            break;

        case 4:
            alert(girl + " wants you to ask her out.");
            break;

        default:
            console.log(i);
    }

So, there is no need to have pare expressions in each case.

When you declare a switch, the variable used is pared to each case, so evaluations are not necessary.

Also it may help to parse your answer from 'r' into an integer for the sake of keeping the variable types in check.

function response() {
    var girl = prompt("What girl do you like?");
    var r = parseInt((Math.random() * (3 - 1 + 1) + 1).toFixed(0));
    var i = r;

    switch(i) {
        case 1:
            alert(girl + " likes you as a friend.");
            break;

        case 2:
            alert(girl + " does not really like you.");
            break;

        case 3:
            alert(girl + " has a crush on you.");
            break;

        case 4:
            alert(girl + " wants you to ask her out.");
            break;

        default:
            console.log(i);
   }
}

switch is paring strict.

You need either

switch (i) {
    case 1:
        alert(girl + " likes you as a friend.");
        break;

Or

switch (true) {
    case i === 1:
        alert(girl + " likes you as a friend.");
        break;

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