What is outcome of (n%2)

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Sir, i'm confuse in !(n%2) what was the result of this . I know it's true or false but what was the outcome of (n%2) plz help i'm totally confuse

What I have tried:

I'm see the code someone else in that he assign a function that has argument n & that is tested for prime no.
code is:

let isPrime = function(n){
if(n === 2){
return true;
}
if((n < 2) || !(n%2) || !Number.isInteger(n)){
return false;
}

for(let i = 3; i < n - 1; i++){
if(n%i === 0){
return false;
}
}
return true;
}

Posted 1-Aug-18 2:51am

Member 13934101

Updated 1-Aug-18 4:04am

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OriginalGriff · Answer 1 · 2018-08-01T02:54:00

Solution 1

It's not "true" or "false" it's 0 or 1: % is a modulus operator which returns the remainder when the left side is divided by the right. And since anything divided by two can only ever have a remainder of zero or one, that is what is returned in this case.

If you use modulus with 10 instead of two, it will return the least significant digit of the number: 12345 % 10 will give you 5.

[edit] Typos. lots of typos [/edit]

Posted 1-Aug-18 2:54am

OriginalGriff

Updated 1-Aug-18 2:56am

v4

Comments

Richard Deeming 3-Aug-18 15:12pm

Technically, it's the remainder operator, not the modulus operator. :)

What’s the difference? Remainder vs Modulus – Fabulous Adventures In Coding[^]

raddevus · Answer 2 · 2018-08-01T03:23:00

This is an intriguing question with an interesting function for primes.
Alter the code slightly and you can see the value of n%i each time through the loop and learn how it works.
All you need to do is add one line in the for loop:
~~console.log("n = " + n + " : " + n%i);~~
Actually, this line is better (more clearly shows output)

console.log(n + "%"+i + " = " + n%i);

It'll give the following for isPrime(7);

7%3 =   1
7%4 =   3
7%5 =   2

I updated the jsbin too.

Now, when you run it you will see the value of n%i each time through the loop.

JavaScript

let isPrime = function(n){
if(n === 2){
return true;
}
if((n < 2) || !(n%2) || !Number.isInteger(n)){
return false;
}
for(let i = 3; i < n - 1; i++){
console.log(n + "%"+i + " = " + n%i);
if(n%i === 0){

return false;
}
}
return true;
}

Here's a link to a jsbin I created : JS Bin - Collaborative JavaScript Debugging[^]
You can go there and see isPrime(7) run when you click the Run with JS button.
You need to open the browser's console window (F12 in most browsers) to see the console.log output.

Patrice T · Answer 3 · 2018-08-01T04:05:00

As you already tested for factor 2, you don't need to test other even numbers.
Replace

JavaScript

for(let i = 3; i < n - 1; i++){

with

JavaScript

for(let i = 3; i < n - 1; i+=2){

and you are twice as quick.
setting the end of loop at square root of n, will also dramatically improve the speed.
For a prime around 10000
your routine will loop about 10000 times
with the i+=2, it will loop 5000 times
with endding at square root, it will loop 50 times

What is outcome of (n%2)

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