The use of "?" and ":"

Question

I've read through a lot of code where they have if statements, i've noticed other languages use this to. Asp being one. Tried googling but couldn't find a answer for it.

What exactly does ?: stand for and when to use it.

As far as I'm aware ? is equal to if() and : being equal to }else{.

Is it `?:` your are looking for, or `bool ? true : false`. Because `?:` would lead to something like `value1 ?: value2` using `value1` if it evaluates to true. — steveoh, Mar 15 '12 at 23:24
possible duplicate of [What is ?: in PHP 5.3?](http://stackoverflow.com/questions/2153180/what-is-in-php-5-3) — mario, Mar 15 '12 at 23:47
And http://stackoverflow.com/questions/3737139/reference-what-does-this-symbol-mean-in-php — mario, Mar 15 '12 at 23:48

Oliver Charlesworth · Answer 1 · 2012-03-15T23:32:28.713

7

It is the ternary operator (although in most languages it is better-named as the "conditional operator").

People will often erroneously refer to it as "shorthand if/else". But this is a misnomer; if/else is a statement, ?: is an expression. In most languages, these are distinct concepts, with different semantics.

edited Mar 15 '12 at 23:32

answered Mar 15 '12 at 23:21

Oliver Charlesworth

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score 2 · Accepted Answer · answered Mar 15 '12 at 23:22

2

This is called ternary operator.

It is meant to simplify code in some cases. Consider this:

var str;

if(some_condition)
  str = 'yes';
else
  str = 'no';

This can be easily rewritten as

var str = some_condition ? 'yes' : 'no';

answered Mar 15 '12 at 23:22

Sergio Tulentsev

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+1 Although, I'd say it's more syntactic sugar, the logic is the same. – Peter Mar 15 '12 at 23:25
@Peter: here - yes. In general - not the same. – Sergio Tulentsev Mar 15 '12 at 23:27
What I meant by "logic is the same" is that it doesn't simplify anything. – Peter Mar 15 '12 at 23:30
1

As @OliCharlesworth correctly points out, `if/else` and ternary operator have different semantics. `if/else` is a control flow structure, ternary operator is an expression. – Sergio Tulentsev Mar 15 '12 at 23:31
@Peter: code is shorter and easier to read. To me this looks like simplification :) – Sergio Tulentsev Mar 15 '12 at 23:32
I know, we're just misunderstanding each other over semantics :) – Peter Mar 15 '12 at 23:33

score 1 · Answer 3 · answered Mar 15 '12 at 23:21

1

Your assumption is right.

It is a Ternary operation (Wikipedia)

answered Mar 15 '12 at 23:21

Daan Timmer

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score 1 · Answer 4 · answered Mar 15 '12 at 23:22

Essentially, the syntax is condition ? then-expession : else-expression. Typically it is used in assigning variables:

varname = something == 123 ? "yes" : "no";

But it can be used pretty much anywhere in place of a value. It's mostly useful for avoiding repetitive code:

if( something == 123) {
    varname = "yes";
}
else {
    varname = "no";
}

Justin · Answer 5 · 2012-03-15T23:38:06.497

0

In Java, it's an if/else relationship.

An example of a ternary operation:

boolean bool = (x==1) ? true : false;

http://en.wikipedia.org/wiki/Ternary_operation

edited Mar 15 '12 at 23:38

answered Mar 15 '12 at 23:21

Justin

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That's a pretty bad example, as it could be replaced with `(x==1)`. – Oliver Charlesworth Mar 15 '12 at 23:24
I wouldn't say it's a bad example, it's a redundant piece of code. It was used an an example, not as best software practice. – Justin Mar 15 '12 at 23:28
Actually, it's currently a syntax error (in most programming languages...) – Oliver Charlesworth Mar 15 '12 at 23:30
better? :-) private static boolean getBoolean(int x) { return (x==1) ? true : false; } – Justin Mar 15 '12 at 23:36

score 0 · Answer 6 · answered Mar 15 '12 at 23:21

0

You could read the documentation. The section you're looking for is titled "Ternary Operator".

answered Mar 15 '12 at 23:21

Carl Norum

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score 0 · Answer 7 · answered Mar 15 '12 at 23:23

You can express calculations that might otherwise require an if-else construction more concisely by using the conditional operator. For example, the following code uses first an if statement and then a conditional operator to check for a possible division-by-zero error before calculating the sin function.

    if(x != 0.0) s = Math.Sin(x)/x; else s = 1.0;
    s = x != 0.0 ? Math.Sin(x)/x : 1.0;

from http://msdn.microsoft.com/en-us/library/ty67wk28(v=vs.90).aspx

The use of "?" and ":"

7 Answers7