JavaScript/JScript: Control Structures I - Pearson Learning Solutions

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Chapter 14 JavaScript/JScript: Control Structures I 409
Common Programming Error 14.3
Placing a semicolon after the condition in an if structure leads to a logic error in singleselection
if structures and a syntax error in double-selection if structures (if the if part
contains a nonempty body statement). 14.3
Good Programming Practice 14.4
Some programmers prefer to type the beginning and ending braces of compound statements
before typing the individual statements within the braces. This helps avoid omitting one or
both of the braces. 14.4
14.7 The while Repetition Structure
A repetition structure allows the programmer to specify that an action is to be repeated
while some condition remains true. The pseudocode statement
While there are more items on my shopping list
Purchase next item and cross it off my list
describes the repetition that occurs during a shopping trip. The condition “there are more
items on my shopping list” may be true or false. If it is true, then the action “Purchase next
item and cross it off my list” is performed. This action will be performed repeatedly while
the condition remains true. The statement(s) contained in the while repetition structure constitute
the body of the while. The while structure body may be a single statement or a compound
statement. Eventually, the condition will become false (when the last item on the
shopping list has been purchased and crossed off the list). At this point, the repetition terminates,
and the first pseudocode statement after the repetition structure is executed.
Common Programming Error 14.4
Not providing in the body of a while structure an action that eventually causes the condition
in the while to become false is a logic error. Normally, such a repetition structure will
never terminate—an error called an “infinite loop.” Browsers handle infinite loops differently.
For example, Internet Explorer allows the user to terminate the script containing the
infinite loop. 14.4
Common Programming Error 14.5
Spelling the keyword while with an uppercase W as in While (remember that JavaScript
is a case-sensitive language) is a syntax error. All of JavaScript’s reserved keywords, such
as while, if and else, contain only lowercase letters. 14.5
As an example of a while structure, consider a program segment designed to find the
first power of 2 larger than 1000. Suppose variable product has been initialized to 2.
When the following while structure finishes executing, product contains the result:
var product = 2;
while ( product