#if Not Debug in c#?

You would need to use:

#if !DEBUG
    // Your code here
#endif

Or, if your symbol is actually Debug

#if !Debug
    // Your code here
#endif

From the documentation, you can effectively treat DEBUG as a boolean. So you can do complex tests like:

#if !DEBUG || (DEBUG && SOMETHING)

Just so you are familiar with what is going on here, #if is a pre-processing expression, and DEBUG is a conditional compilation symbol. Here's an MSDN article for a more in-depth explanation.

By default, when in Debug configuration, Visual Studio will check the Define DEBUG constant option under the project's Build properties. This goes for both C# and VB.NET. If you want to get crazy you can define new build configurations and define your own Conditional compilation symbols. The typical example when you see this though is:

#if DEBUG
    //Write to the console
#else
    //write to a file
#endif