Add(a,b).ToString()
А out используют в любом случае где хотят вернуть из метода больше чем 1 значение
• Output parameters do not need to be initialized before they passed to the method.
The reason for this is that the method must assign output parameters before exiting.
• Reference parameters must be initialized before they are passed to the method.
The reason for this is that you are passing a reference to an existing variable. If you
don’t assign it to an initial value, that would be the equivalent of operating on an
unassigned local variable.
