?? in C# (double question mark operator in C#) Or null coalescing operator

null coalescing operator

The operator "??", yes two question marks. called as  "null-coalescing" or just the double question mark operator.

According to the Microsoft, help page: "The ?? operator returns the left-hand operand if it is not null, or else it returns the right operand."

eg : var result = answer1 ?? answer2;
            can also be written as below
var result = answer1 != null ? answer1 : answer2;

if answer1 is not null =>
     result = answer1

if answer1 is null =>
   result = answer2

?? will be better uasable when we have to check for multiple null values for a result

string result = answer1 ?? answer2 ?? answer3 ?? answer4;

For more information please check
https://stackoverflow.com/questions/446835/what-do-two-question-marks-together-mean-in-c

Process with an ID ???? is not running in visual studio 2015

Possible Solution 1: 

• Close VS.
• Navigate to the folder of the solution and delete the hidden .vs folder.
• Restart VS.
• Hit F5 and IIS Express should load as normal, allowing you to debug.

Possible Solution 2: 

• Close all instances of Visual Studio
• Rename the IISExpress folder (in my PC is in C:\Users\jmelosegui\Documents)
• Add the _CSRUN_DISABLE_WORKAROUNDS Environment System variable with the value of 1. Here is how.
• Start Visualstudio in administrator mode

Possible Solution 3:

• open vs as an administrator
• right click project and click on unload project
• again right click project and click on open edit.... csproj
• find the code below and delete it $

  <DevelopmentServerPort>63366</DevelopmentServerPort>
  <DevelopmentServerVPath>/</DevelopmentServerVPath>
  <IISUrl>http://localhost:63366/</IISUrl>
  

• save and close the file .csproj
• right click project and reload it

Source : https://stackoverflow.com/questions/26424902/process-with-an-id-is-not-running-in-visual-studio-professional-2013-update