I want to check if an object is not of a particular type. I know how to check if something is of a particular type:
if (t is TypeA) { ... }
UPDATE 2020-10-30:
Times are changing. Starting from C# 9.0 you can use more natural way of checking it:
if(t is not TypeA) { ... }
ORIGINAL ANSWER:
C# is not quite natural language ;) Use this one
if(!(t is TypeA)) { ... }