x = 5 first_Time = false formZipcode = 92683 in Java

Paint Code 3/9 in Java x = 5 first_Time = false formZipcode = 92683

In the preceding example, x contains the numeric value of 5 However, the formZipcode variable contains a text string, not a number, because the string value is enclosed in double quotes If you need to perform mathematical operations on a variable, assign a number value to it, not a quoted string The actual act of creating a variable and assigning it a value is called declaring the variable So, to declare the variable pi to be equal to 314, you write this:

because they each have different capitalization Variable names can use only letters, numbers, and underscores They can t contain spaces or other punctuation Variable names can t start with a number Variable names can t be the same as a reserved word Reserved words are special keywords, such as if or with, that are used by JavaScript for its core functionality Make sure you avoid naming a variable the same as one of these words A complete list of reserved words is available at wwwjavascripternet/faq/reservedhtm

When you work with a literal value or variable, JavaScript categorizes it as a particular data type Table 13-1 shows the common types of values

13: The Nuts and Bolts of JavaScript Table 13-1

Type Number String Object Description Any numeric value Text characters inside quote marks A JavaScript object, which can be defined by the language or else created on your own Value returned by a function A true or false value Empty; has no value

As the preceding sections discuss, a literal value (such as 5 and Lightbulb ) or a variable can represent a value of a particular type However, in JavaScript, a complete statement, called an expression, can also return a value For example, consider the following two expressions:

2+1+2 A + three + hour + tour // Evaluates to a value of 5 // Evaluates to Athreehourtour

As you can see from these two examples, JavaScript often uses symbols as you evaluate, manipulate, and work with expressions These symbols are called operators In the examples shown above, the + symbol is used to either add numeric values or to concatenate two or more strings together into a single one JavaScript has several different types of operators, including assignment, arithmetic, counting, and comparison types

Assignment operators put values into variables For example, x = 8 assigns the value of 8 to the variable x Table 13-2 shows the assignment operators, although as you can see, they really combine assignment and arithmetic functionality

Part IV: Integrating Scripts with HTML Table 13-2

Assignment Description Sets x to the value of y Same as x=x + y Same as x = x - y Same as x = x * y Same as x = x / y

When you feel like crunching numbers, use arithmetic operators You ll quickly recognize these symbols from your high-school math class Expressions with the most common operators are listed in Table 13-3

Table 13-3

+ * / -

Description Adds x and y together Subtracts y from x Multiplies x and y together Divides x by y Reverses the sign of x

JavaScript provides operators that are especially designed for counting either up or down while a process runs The same operator can Retrieve a variable Count up or count down Table 13-4 shows the counting operators

Table 13-4

x++ --x x--

Description Increases x by 1 after an assignment Decreases x by 1 (same as x = x - 1) before an assignment Decreases x by 1 after an assignment

When you place the ++ or -- operators before the variable, the value of the variable changes before you use the variable For example, if x is 8, y= ++x changes the variables in this order: 1 Set x to 9 2 Set y to 9