+= Operator (C# Reference)


Updated: July 20, 2015

For the latest documentation on Visual Studio 2017 RC, see Visual Studio 2017 RC Documentation.

The addition assignment operator.

An expression using the += assignment operator, such as

x += y  

is equivalent to

x = x + y  

except that x is only evaluated once. The meaning of the + operator depends on the types of x and y (addition for numeric operands, concatenation for string operands, and so forth).

The += operator cannot be overloaded directly, but user-defined types can overload the + operator (see operator).

The += operator is also used to specify a method that will be called in response to an event; such methods are called event handlers. The use of the += operator in this context is referred to as subscribing to an event. For more information, see How to: Subscribe to and Unsubscribe from Events. and Delegates.

    class AddAssigment
        static void Main()
            int a = 5;
            a += 6;

            //string concatenation
            string s = "Hello";
            s += " world.";
    Hello world

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C# Operators