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+ Operator (C# Reference)

The + operator can function as either a unary or a binary operator.

Unary + operators are predefined for all numeric types. The result of a unary + operation on a numeric type is just the value of the operand.

Binary + operators are predefined for numeric and string types. For numeric types, + computes the sum of its two operands. When one or both operands are of type string, + concatenates the string representations of the operands.

Delegate types also provide a binary + operator, which performs delegate concatenation.

User-defined types can overload the unary + and binary + operators. Operations on integral types are generally allowed on enumeration. For more information, see operator (C# Reference).

class Plus
    static void Main()
        Console.WriteLine(+5);        // unary plus
        Console.WriteLine(5 + 5);     // addition
        Console.WriteLine(5 + .5);    // addition
        Console.WriteLine("5" + "5"); // string concatenation
        Console.WriteLine(5.0 + "5"); // string concatenation
        // note automatic conversion from double to string

For more information, see the C# Language Specification. The language specification is the definitive source for C# syntax and usage.