Chapter 7:The Repetition Structure

Introduction to Programming with C++

Fourth Edition

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Objectives

• Include a repetition structure in pseudocode and in a flowchart

• Code a pretest loop using the C++ while statement

• Initialize and update counters and accumulators• Code a pretest loop using the C++ for statement

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Using the Repetition Structure

• Repetition structure or loop - allows repeated processing of one or more program instructions until some condition is met

• Repetition structure can be either a pretest loop or a posttest loop– Pretest loop: evaluation occurs before loop

instructions are processed– Posttest loop: evaluation occurs after loop

instructions are processed

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Pretest Loops

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Pretest Loops (continued)

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Pretest Loops (continued)

• Every loop has:– a loop condition– a loop body

• Loop body: – instructions within a loop

• Loop condition: – appears at the beginning of a pretest loop– determines the number of times instructions

within the loop are processed

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• Sentinel value – special value to end the loop

• Priming read:– Appears above the loop– Used to prepare or set up the loop

Pretest Loops (continued)

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Components of a Loop

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O’Donnell Incorporated Algorithm Shown in Flowchart Form

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Using the while Statement to Code the Pretest Loop

• While statement: programmer must supply the loop condition to be evaluated

• Loop condition:– must be a Boolean expression (true or false)– can contain variables, constants, functions,

methods, arithmetic operators, comparison operators, and logical operators

• Endless or infinite loop – one that processes its instructions indefinitely

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Syntax of the C++ while Statement

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Using Counters and Accumulators

• Counter - a numeric variable used for counting

• Accumulator - a numeric variable used for accumulating a value

• Initializing - assigning a beginning value to the counter or accumulator

• Updating or incrementing - adding a number to the value stored in the counter or the accumulator

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Counter-Controlled Pretest Loops

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Using the for Statement to Code a Pretest Loop

• Most common use for the for statement:– Code pretest loops whose processing is

controlled by a counter• For statement:

– Begins with the for clause– Followed by the body of the loop

• If the loop body contains more than one statement:– Statements must be entered as a statement block

i.e., enclosed in braces ({})

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Syntax of the C++ for statement

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for Statement Displays the Numbers 1 Through 3

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for Statement Calculates and Displays a Commission

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for Statement Calculates and Displays a Bonus

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Summary

• Repetition structure or loop - allows repeated processing of one or more program instructions until some condition is met – Repetition structures contain a condition and

a loop body