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

Solution 1:

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.

Solution 2:

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.

Solution 3:

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).

Solution 4:

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=";
}

Solution 5:

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.