+= Operator (Visual Basic)
Updated: July 20, 2015
For the latest documentation on Visual Studio 2017, see Visual Studio 2017 Documentation.
Adds the value of a numeric expression to the value of a numeric variable or property and assigns the result to the variable or property. Can also be used to concatenate a
String expression to a
String variable or property and assign the result to the variable or property.
variableorproperty += expression
Required. Any numeric or
String variable or property.
Required. Any numeric or
The element on the left side of the
+= operator can be a simple scalar variable, a property, or an element of an array. The variable or property cannot be ReadOnly.
+= operator adds the value on its right to the variable or property on its left, and assigns the result to the variable or property on its left. The
+= operator can also be used to concatenate the
String expression on its right to the
String variable or property on its left, and assign the result to the variable or property on its left.
When you use the
This assignment operator implicitly performs widening but not narrowing conversions if the compilation environment enforces strict semantics. For more information on these conversions, see Widening and Narrowing Conversions. For more information on strict and permissive semantics, see Option Strict Statement.
If permissive semantics are allowed, the
+= operator implicitly performs a variety of string and numeric conversions identical to those performed by the
+ operator. For details on these conversions, see + Operator.
+ operator can be overloaded, which means that a class or structure can redefine its behavior when an operand has the type of that class or structure. Overloading the
+ operator affects the behavior of the
+= operator. If your code uses
+= on a class or structure that overloads
+, be sure you understand its redefined behavior. For more information, see Operator Procedures.
The following example uses the
+= operator to combine the value of one variable with another. The first part uses
+= with numeric variables to add one value to another. The second part uses
String variables to concatenate one value with another. In both cases, the result is assigned to the first variable.
' This part uses numeric variables. Dim num1 As Integer = 10 Dim num2 As Integer = 3 num1 += num2
' This part uses string variables. Dim str1 As String = "10" Dim str2 As String = "3" str1 += str2
The value of
num1 is now 13, and the value of
str1 is now "103".