: ? Operators Instead of If|Else

?: ?? Operators Instead Of IF|ELSE

For [1], you can't: these operators are made to return a value, not perform operations.

The expression

a ? b : c

evaluates to b if a is true and evaluates to c if a is false.

The expression

b ?? c

evaluates to b if b is not null and evaluates to c if b is null.

If you write

return a ? b : c;

return b ?? c;

they will always return something.

For [2], you can write a function that returns the right value that performs your "multiple operations", but that's probably worse than just using if/else.

Use of ternary operator instead of if-else in C++

No. In general the conditional operator is not a replacement for an if-else.

The most striking difference is that the last two operands of the conditional operator need to have a common type. Your code does not work eg with:

std::string do_this() {return {};}
void do_that() {}

There would be an error because there is no common type for void and std::string:

<source>: In function 'int main()':
<source>:15:22: error: third operand to the conditional operator is of type 'void', but the second operand is neither a throw-expression nor of type 'void'
   15 |     my_flag ? do_this() : do_that();
      |               ~~~~~~~^~

Moreover, the conditional operator is often less readable.

The conditional operator can be used for complicated in-line initialization. For example you cannot write:

 int x = 0;
 int y = 0;
 bool condition = true;
 int& ref;                                 // error: must initialize reference
 if (condition) ref = x; else ref = y;     // and even then, this wouldn't to the right thing

but you can write

 int& ref = condition ? x : y;

My advice is to not use the conditional operator to save some key-strokes compared to an if-else. It is not always equivalent.

PS: The operator is called "conditional operator". The term "ternary operator" is more general, like unary or binary operator. C++ just happens to have only a single ternary operator (which is the conditional operator).

Can we use '?' operator instead of nested-if condition?

You forgot to add a part of the expression. Try it as follows:

int i = (10>5) ? ( (2<5) ? 230:456 ) : 0;

Replace the above 0 to be the desired number you want your variable to be when your first condition (10>5) is false.

Using the ternary operator instead of if/else?

The ternary syntax is conditional ? true : false. You've combined multiple if conditional ternaries here, though no logic for if none of the conditionals are met. To correct this, add fallback behavior of : false after your final conditional:

var age = 15;
function whichSchool(age) {  return (age < 13) ? "Elementary School"       : (age >= 13 && age <= 18) ? "Secondary School"       : (age > 18) ? "University"       : "None"}
console.log(whichSchool(15))

Use Ternary operator instead of if..else in javascript

There are multiple ways to write a conditional statement in JS. However, if there are multiple statements I would say you should stick to if else if else. But if you want to see other approaches, here they are:

Using Ternary operator ? :

const {pr} = req.query
pr === 'trans'
? util.transUrl(req.originalUrl).then(param => 
      res.redirect(param)
  )
: pr === 'inst'
? util.instaUrl(req.originalUrl).then(param => 
      res.redirect(param)
  )
: res.status(400).send('Contact the editor of the originating page.')

Using Gate logic && ||

const {pr} = req.query
(pr === 'trans' && 
    util.transUrl(req.originalUrl).then(param => 
        res.redirect(param))
) ||
(pr=== 'inst' && 
    util.instaUrl(req.originalUrl).then(param => 
        res.redirect(param))
) || 
res.status(400).send('Contact the editor of the originating page.')

Now, Looking at your code, here if and else if statements are similar. So you can avoid else if using ternary operator like this:

const {pr} = req.query
if(pr === 'trans' || pr === 'inst'){
    util[pr === 'trans' ? 'transUrl' : 'instaUrl'](req.originalUrl)
    .then(param => res.redirect(param))
}
else{
    res.status(400).send('Contact the editor of the originating page.')
}

Just one FYI: Please consider using === instead of == whenever you are comparing strings and there is no need of coercion.

Ternary operator ?: vs if...else

Depends on your compiler, but on any modern compiler there is generally no difference. It's something you shouldn't worry about. Concentrate on the maintainability of your code.

Using ternary operators instead of if statement when returning variable

Is returning null a proper way to hide Components?

Yes, returning null is a valid return value for a React Component. See this section of the official documentation:

Booleans, Null, and Undefined Are Ignored

false, null, undefined, and true are valid children. They simply don't render.

You could shorten your code a bit though:

const Component = ({data, onChange}) => (
  data && data.length ? <ul>
    {data.map(( item ) => <Item onChange={ onChange } />)}
  </ul> : null
)

Note however that you are not using item inside <Item>. Is that intentional? If so, you can write instead: {data.map(() => <Item onChange={ onChange } />)}

Also note that you need to provide a key property to each <Item>. I have not added that to my snippet, but you can read more about the key prop, here.

Javascript usage of && operator instead of if condition

What always helps me is translating it to words

var r = 0;
var i = 10;
r == 0 && (r = i);

translates to

set variable r to zero
set variable i to ten
if variable r equals zero AND the return of the following statement "set variable r to value of variable i"
do nothing, but r is now 10.

so in short, let's forget about 1 and 2.

In javascript the execution flow in a boolean comparisan is to stop execution of if statement parameters if any part from the && fails.

An boolean comparisan will execute from left to right.

1 == 1 && 2 == 3 && (r = i)

it will pass 1 == 1 fail on 2 == 3 and never reach the assigment operation.

Basically it's a shorthand for:

if(r == 0) {
   r = i;
}

: ? Operators Instead of If|Else