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Addition operators - + and += |
The C# addition operators (`+`, and `+=`) work with operands of numeric, string, or delegate types. |
11/29/2022 |
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The + and += operators are supported by the built-in integral and floating-point numeric types, the string type, and delegate types.
For information about the arithmetic + operator, see the Unary plus and minus operators and Addition operator + sections of the Arithmetic operators article.
When one or both operands are of type string, the + operator concatenates the string representations of its operands (the string representation of null is an empty string):
[!code-csharp-interactivestring concatenation]
String interpolation provides a more convenient way to format strings:
[!code-csharp-interactivestring interpolation]
Beginning with C# 10, you can use string interpolation to initialize a constant string when all the expressions used for placeholders are also constant strings.
Beginning with C# 11, the + operator performs string concatenation for UTF-8 literal strings. This operator concatenates two ReadOnlySpan<byte> objects.
For operands of the same delegate type, the + operator returns a new delegate instance that, when invoked, invokes the left-hand operand and then invokes the right-hand operand. If any of the operands is null, the + operator returns the value of another operand (which also might be null). The following example shows how delegates can be combined with the + operator:
[!code-csharp-interactivedelegate combination]
To perform delegate removal, use the - operator.
For more information about delegate types, see Delegates.
An expression using the += operator, such as
x += yis equivalent to
x = x + yexcept that x is only evaluated once.
The following example demonstrates the usage of the += operator:
[!code-csharp-interactive+= examples]
You also use the += operator to specify an event handler method when you subscribe to an event. For more information, see How to: subscribe to and unsubscribe from events.
A user-defined type can overload the + operator. When a binary + operator is overloaded, the += operator is also implicitly overloaded. A user-defined type can't explicitly overload the += operator.
For more information, see the Unary plus operator and Addition operator sections of the C# language specification.