Adds the value of an expression to the value of a variable and assigns the result to the variable.
result += expression
Any variable.
Any expression.
Using this operator is exactly the same as specifying:
result = result + expression
The underlying subtype of the expressions determines the behavior of the += operator.
Both expressions are numeric or Boolean
Add
Both expressions are strings
Concatenate
One expression is numeric and the other is a string
Version 1