-= Operator (C# Reference)

The subtraction 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 is dependent on the types of x and y (subtraction for numeric operands, delegate removal for delegate 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 in C# to unsubscribe from an event. For more information, see How to: Subscribe to and Unsubscribe from Events (C# Programming Guide).

    class MainClass3
    {
        static void Main()
        {
            int a = 5;
            a -= 6;
            Console.WriteLine(a);
        }
    }
    /*
    Output:
    -1
    */

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