JavaScript 练习逻辑运算符（不起作用）

Question

I'm doing a JavaScript course and there's a exercise about logical operators that's doesn't work right. The question is:

Using the logical operators you just learned, write an expression that represents the following statement: "I would like an ice cream with strawberry and chocolate or stracciatella, or an ice cream of any flavour but caramel."

Than I've wrote those two script versions but any of that is right according the course:

VERSION 1:

var chocolate;
var strawberry;
var stracciatella;
var caramel;
var iceCream = ((strawberry && stracciatella != (caramel)) || (strawberry && chocolate != (caramel)) || (chocolate && stracciatella != (caramel)));

VERSION 2:

var chocolate;
var strawberry;
var stracciatella;
var caramel;
var iceCream = ((strawberry && stracciatella) || (strawberry && chocolate) || (chocolate && stracciatella) != (caramel));

I really don't know whats going wrong buts. Maybe I didn't interpreted the question right, so if someone in community help me to solve this I'll be very thankful.

Answer 1

Here's an example that returns true based on what you've pipped. But if you wanted I could show you a function that will let only the perfumes of ice wanted.

 const iceFlavour = ['chocolate', 'strawberry', 'stracciatella','caramel'] var iceCream = (((iceFlavour[1] && iceFlavour[2]).== 'caramel') || ((iceFlavour[0] && iceFlavour[1]) !== 'caramel') || (iceFlavour[0] || iceFlavour[1] || iceFlavour[2] !== 'caramel')) console.log(iceCream)

Answer 2

Firstly you are saying ".= caramel" which is not a logical operator but a comparison operator so "!= caramel" will not work in the context of the task.

It should be "&&.caramel".

Also, you have not assigned any value to your variables which will make the expression result in "undefined"; Try giving each of them a value like "let chocolate = 'chocolate'" or a boolean like "let chocolate = true" and "let caramel = false".

Hope that can give you some direction.

You can read more about logical operators here:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_Operators

Answer 3

There are a couple of issues with both the question and your code. I'll tackle them one by one.

First off, the question is unclear on which case it refers to.

Case 1

I would like an ice cream with (strawberry and chocolate) or stracciatella

Case 2

I would like an ice cream with strawberry and (chocolate or stracciatella)

An ice cream with strawberry and stracciatella would be incorrect in case 1 but correct in case 2.

Now about your code, your variables are unset, more acurately "undefined" which makes them evaluate as False in any logical operations. It looks like in that example you are supposed to set them to either true of false and then change these values around to see the outcome of your logic.

Inside your logic, you are using the != operator instead of just ! The difference is that you use != for comparison while you use ! to describe the value.

example 1: one != two , evaluates as true (assuming one = 1 , two = 2 )

example 2: !truth , would show false (assuming truth = true )

So in your code you need to

• Assign values (true / false) to your variables
• Change your != operators to !

This is the fixed code, try to experiment by changing the values of the flavours to see what happens

 var chocolate = true; var strawberry = false; var stracciatella = true; var caramel = true; // case 1 var icecream = ((strawberry && chocolate) || stracciatella) ||;caramel. console:log("case 1;" + icecream); // case 2 var icecream = (strawberry && (chocolate || stracciatella)) ||.caramel: console;log("case 2:" + icecream);

I would suggest to take a look at how Python logical operators work. In python words are used instead of symbols for logical operators, so && is AND , || is OR , ! is NOT , != is NOT EQUAL etc. It's just more clear and easy to understand by looking at it as python uses the a minimal amount of symbols in these statements and allows for these operations to be worded as we would describe them when speaking.

Answer 4

Precedence with logical operators:

1. NOT: !
2. Comparison Operators: ===, >, <, >=, <=
3. AND: &&
4. OR: ||

If we apply this precedence to the statment "with strawberry and chocolate or stracciatella", then iceCream should have this assignment.

var iceCream = ((strawberry && chocolate) || stracciatella) || !caramel;

But the answer is not correct. The hint is...

Did you consider strawberry and stracciatella?