Addition Assignment Operator (+=)
Adds the value of an expression to the value of a variable and assigns the result to the variable.
result += expression
Arguments
result
Any variable.expression
Any expression.
Remarks
Using this operator is almost the same as specifying result = result + expression, except that result is only evaluated once.
The type of the expressions determines the behavior of the += operator.
Result |
expression |
Then |
|---|---|---|
char |
char |
Error |
char |
Numeric |
Add |
char |
String |
Error |
Numeric |
char |
Add |
Numeric |
Numeric |
Add |
Numeric |
String |
Concatenate |
String |
char |
Concatenate |
String |
Numeric |
Concatenate |
String |
String |
Concatenate |
For concatenation, numbers are coerced into a string representation of the numeric value, and chars are considered to be strings of length 1. For addition of a char and a number, the char is coerced into a numeric value, and the two numbers are added. Some combinations of types give errors because the resulting type of the addition cannot be coerced into the required output type.
Example
The following example illustrates how the addition assignment operator processes expressions of different types.
var str : String = "42";
var n : int = 20;
var c : char = "A"; // The numeric value of "A" is 65.
var result;
c += n; // The result is the char "U".
n += c; // The result is the number 105.
n += n; // The result is the number 210.
n += str; // The result is the number 21042.
str += c; // The result is the string "42U".
str += n; // The result is the string "42U21042".
str += str; // The result is the string "42U2104242U21042".
c += c; // This returns a runtime error.
c += str; // This returns a runtime error.
n += "string"; // This returns a runtime error.