Джейк прав. Оператор + = не является перегруженной функцией в C #.
амма на C #:
short a, b;
a = 10;
b = 10;
a = a + b; // Error : Cannot implicitly convert type 'int' to 'short'.
// we can also write this code by using Arithmetic Assignment Operator as given below
a += b; // But this is running successfully, why?
Console.Write(a);