Java How to Program Fourth Edition - DCC

Chapter 4 Control Structures: Part 1 159
Software Engineering Observation 4.3
Just as a block can be placed anywhere a single statement can be placed, it is also possible
to have no statement at all (i.e., the empty statement in such places). The empty statement is
represented by placing a semicolon (;) where a statement would normally be. 4.3
Common Programming Error 4.3
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). 4.3
Good Programming Practice 4.5
Some programmers prefer to type the beginning and ending braces of blocks before typing
the individual statements within the braces. This practice helps avoid omitting one or both of
the braces. 4.5
In this section, we have introduced the notion of a block. A block may contain declarations
(as does the body of main, for example). The declarations in a block commonly are
placed first in the block before any action statements occur, but declarations may also be
intermixed with action statements.
4.7 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 structure. The body of the while structure may be a single statement
or a block. 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 4.4
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. 4.4
Common Programming Error 4.5
Spelling the keyword while with an uppercase W, as in While, is a syntax error. (Remember
that Java is a case-sensitive language.) All of Java’s reserved keywords, such as while,
if and else, contain only lowercase letters. 4.5
As an example of a while structure, consider a program segment designed to find the
first power of 2 larger than 1000. Suppose that the int variable product has been initialized
to 2. When the following while structure finishes executing, product contains
the result:
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