The
arithmetic
operators perform mathematical operations on numeric operands. If you
use non-numeric operands with the arithmetic operators, ActionScript
will attempt to convert the foreign data to a number. For example,
`false - true`

evaluates to -1 because
`false`

converts to the numeric value
and `true`

converts to 1. Similarly, the expression
`"3" * "5"`

results in the number 15, because the
strings “3” and “5” are converted to the
numbers 3 and 5 before the multiplication is performed. The
`+`

operator, however, presents a special case: when
used with at least one string operand, it performs a string
concatenation operation, not mathematical addition.

If
an attempt to
convert a non-numeric operand to a number fails, the operand will be
set to the special numeric value `NaN`

. This results
in the entire operation yielding `NaN`

. Refer to
Table 3.1 for details on numeric conversion.

The
*addition*
operator returns the sum of its two operands:

+`operand1`

`operand2`

In order to return a meaningful mathematical result, the operands of
`+`

should be expressions that yield a numeric
value, such as:

234 + 5 // Returns 239 (2 * 3 * 4) + 5 // Returns 29

The addition operator is unique among the arithmetic operators in that if one or both of its operands are strings, it performs as a string concatenation. Refer to Section 4.6.1 in Chapter 4.

A
handy variation on addition, the
*increment* operator accepts a single operand and simply adds 1 to its current value. Increment ...

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