Question mark and colon in statement. What does it mean?

Question

What do the question mark (?) and colon (:) mean?

((OperationURL[1] == "GET") ? GetRequestSignature() : "")

It appears in the following statement:

string requestUri = _apiURL + "?e=" + OperationURL[0] + ((OperationURL[1] == "GET") ? GetRequestSignature() : "");

score 119 · Accepted Answer · edited May 23 '17 at 11:33

119

This is the conditional operator expression.

(condition) ? [true path] : [false path];

For example

 string value = someBooleanExpression ? "Alpha" : "Beta";

So if the boolean expression is true, value will hold "Alpha", otherwise, it holds "Beta".

For a common pitfall that people fall into, see this question in the C# tag wiki.

edited May 23 '17 at 11:33

Community

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answered Aug 05 '11 at 13:40

Anthony Pegram

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value == someBooleanExpression – Yu Zhang Feb 18 '15 at 23:08
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@YuZhang : no, it's correct. Example : string value = 1 == 2 ? "Alpha" : "Beta"; -> value will hold "Beta" – Michaël Polla Apr 02 '15 at 09:22

score 15 · Answer 2 · answered Aug 05 '11 at 13:41

15

It is the ternary conditional operator.

If the condition in the parenthesis before the ? is true, it returns the value to the left of the :, otherwise the value to the right.

answered Aug 05 '11 at 13:41

Oded

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score 7 · Answer 3 · edited Nov 09 '20 at 00:03

7

It's a ternary operator, or the short form for if..else.

condition ? value if true : value if false

See Microsoft Docs | ?: operator (C# reference).

edited Nov 09 '20 at 00:03

Pang

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answered Aug 05 '11 at 13:41

Spooks

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score 1 · Answer 4 · answered Apr 08 '16 at 14:17

This is also known as the "inline if", or as above the ternary operator. https://en.wikipedia.org/wiki/%3F:

It's used to reduce code, though it's not recommended to use a lot of these on a single line as it may make maintaining code quite difficult. Imagine:

a = b?c:(d?e:(f?g:h));

and you could go on a while.

It ends up basically the same as writing:

if(b)
  a = c;
else if(d)
  a = e;
else if(f)
  a = g;
else
  a = h;

In your case, "string requestUri = _apiURL + "?e=" + OperationURL[0] + ((OperationURL[1] == "GET") ? GetRequestSignature() : "");"

Can also be written as: (omitting the else, since it's an empty string)

string requestUri = _apiURL + "?e=" + OperationURL[0];
if((OperationURL[1] == "GET")
    requestUri = requestUri + GetRequestSignature();

or like this:

string requestUri;
if((OperationURL[1] == "GET")
    requestUri = _apiURL + "?e=" + OperationURL[0] + GetRequestSignature();
else
    requestUri = _apiURL + "?e=" + OperationURL[0];

Depending on your preference / the code style your boss tells you to use.

score 1 · Answer 5 · edited Apr 10 '14 at 07:15

1

string requestUri = _apiURL + "?e=" + OperationURL[0] + ((OperationURL[1] == "GET") ? GetRequestSignature() : "");

can be translated to:

string requestUri="";
if ((OperationURL[1] == "GET")
{
    requestUri = _apiURL + "?e=" + GetRequestSignature();
}
else
{
   requestUri = _apiURL + "?e=";
}

edited Apr 10 '14 at 07:15

Dylan Snel

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answered Aug 05 '11 at 13:42

Kimtho6

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score 0 · Answer 6 · answered Aug 05 '11 at 13:41

In the particular case you've provided, it's a conditional assignment. The part before the question mark (?) is a boolean condition, and the parts either side of the colon (:) are the values to assign based on the result of the condition (left side of the colon is the value for true, right side is the value for false).

score 0 · Answer 7 · answered Aug 05 '11 at 13:43

It means if "OperationURL[1]" evaluates to "GET" then return "GetRequestSignature()" else return "". I'm guessing "GetRequestSignature()" here returns a string. The syntax CONDITION ? A : B basically stands for an if-else where A is returned when CONDITION is true and B is returned when CONDITION is false.

Question mark and colon in statement. What does it mean?

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