The logical negation operator (!) is a unary operator that negates its operand. It is defined for bool and returns true if and only if its operand is false.
User-defined types can overload the ! operator (see operator).
using System; class Test { public static void Main() { Console.WriteLine(!true); Console.WriteLine(!false); } }
False True
C# Operators | CLR 7.6.3 Logical negation operator