C# Directive to indicate 32-bit or 64-bit build

Question

Is there some sort of C# directive to use when using a development machine (32-bit or 64-bit) that says something to the effect of:

if (32-bit Vista)
    // set a         


        

Answer 1

Can you do it at runtime?

if (IntPtr.Size == 4)
  // 32 bit
else if (IntPtr.Size == 8)
  // 64 bit