Why use comma inside if statement in C++ or Javascript

Asked Sep 14 '16 at 06:24

Active Sep 14 '16 at 06:37

Viewed 102 times

I researched a lot and found out that comma inside an if statement is :

In the C and C++ programming languages, the comma operator (represented by the token ,) is a binary operator that evaluates its first operand and discards the result, and then evaluates the second operand and returns this value (and type).

and in javascript is something like C and C++

But still it is unclear to me, I can't get it why should I use some statements like these :

int a = 1, b = 0;

if(a, b) // it is `false` because b is 0 --> if(0)

if(b, a) // it is `true` because a is 1 --> if(1)

Or in a better example:

var number = 10;
console.log(someFunc(number));
function someFunc(number){
    return !(0, isNaN(number));
}
// this results true. 0 is discarded and isNaN(10) is false so !(false) -> true

What is the point of using 0 and , inside return condition ?

This is another link others mentions but they didn't really answered the question. When is the comma operator useful?

edited May 23 '17 at 10:33

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asked Sep 14 '16 at 06:24

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Nothing useful here, but note : _"evaluates its first operand "_ – Sourav Ghosh Sep 14 '16 at 06:27
1

Where did you find those examples? – molbdnilo Sep 14 '16 at 06:28
> When is the comma operator useful? < Well I would say almost never. You are only confusing readers of code. – Ondrej Sep 14 '16 at 07:45
It is useful in a `for` loop, for example `for(x=0, y=0; ; x++, y++)` but is rarely useful elsewhere. – cdarke Sep 14 '16 at 08:41

Why use comma inside if statement in C++ or Javascript

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