6.10: Principles of Loop Design

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Before moving on, it will be useful to summarize the main principles involved in correctly constructing a loop.

A counting loop can be used whenever you know in advance exactly how many iterations are needed. Java’s for statement is an appropriate structure for coding a counting loop.

A while structure should be used when the problem suggests that the loop body may be skipped entirely. Java’s while statement is specially designed for the while structure.

A do-while structure should be used only when a loop requires one or more iterations. Java’s do-while statement is specially designed for the do-while structure.

The loop variable is used to specify the loop-entry condition. It must be initialized to an appropriate initial value, and it must be updated on each iteration of the loop.

A loop’s bound may be a count, a sentinel, or, more generally, a conditional bound. It must be correctly specified in the loop-entry expression, and progress toward the bound must be made in the updater.

An infinite loop may result if the initializer, loop-entry expression, or updater expression is not correctly specified.

The loop types are also summarized in Table 6.1.

lll
Use &If &Java Statement

Counting loop &Number of iterations known in advance &for

While structure &Number of iterations not known &while &Loop may not be entered at all &

Do-while structure &Number of iterations not known &do-while &Loop must be entered at least once &

For each of the following problems, decide whether a counting loop structure, a while structure, or a do-while structure should be used, and write a pseudocode algorithm.

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