What does the colon do in this line of C# programming?

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return url.Contains('.') ? url.Substring(url.LastIndexOf('.')) : "";

I am trying to display the extension of a url given.

What I have tried:

I have used colon (:) in other programming formats but never seen one like this.

Posted 31-Mar-23 3:16am

arpitsrivstva

Updated 31-Mar-23 6:27am

v2

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[no name] 31-Mar-23 13:12pm

I'm guessing you wanted to return the url (instead of a substring) if it didn't contain '.'; and not simply "blank"; e.g. xxx ? yyyy : url;

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Tony Hill · Answer 1 · 2023-03-31T03:53:00

Solution 1

It is the equivalent of the else part of an if else statement.

C#

string something;

if (url.Contains('.')) {
	something = url.Substring(url.LastIndexOf('.'))
} else {
	something = "";
}

return something;

Posted 31-Mar-23 3:53am

Tony Hill

Updated 31-Mar-23 4:28am

v3

OriginalGriff · Answer 2 · 2023-03-31T03:55:00

It's party of a conditional expression:

C#

A = B ? C : D;

If the condition B evaluates to true, then the result of the expression C is assigned to A. Otherwise, the expression D is evaluated and assigned instead.
For example:

C#

string result = x == 0 ? "Zero" : "Nonzero";

result will contain a string describing the "zeroness" of x

pdoxtader · Answer 3 · 2023-03-31T06:27:00

You're looking at a ternary operator. The ternary operator ?: works like a simplified If/Then/else statement.

The first part precedes the question mark, and is an expression that evaluates to true or false. In your carse, it's "url.Contains('.')". The part that immediately follows the question mark is the result if true, and the part follows the colon is the result if false.

So, in your case, "url.Substring(url.LastIndexOf('.'))" is returned is true, and "" is returned if false.

For more information on the ternary operator, have a look at this.

What does the colon do in this line of C# programming?

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