Chapter 1: An Introduction to Control

Structures

Introduction to Programming with C++

Fourth Edition

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Objectives

• Explain the sequence, selection, and repetition structures

• Write simple algorithms using the sequence, selection, and repetition structures

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Defining Control Structures

• All computer programs, no matter how simple or how complex, are written using one or more of three basic structures:– Sequence

– Selection

– Repetition

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The Sequence Structure

• Directs the computer to process the program instructions, one after another, in the order listed in the program

• Rob, the mechanical man, has a limited instruction set (walk, turn, and sit)

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The Sequence Structure

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The Repetition Structure

• Makes a decision, then takes appropriate action based on that decision

– Example: shampoo bottles typically include the repetition structure in the directions for washing your hair

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The Repetition Structure

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The Repetition Structure

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Rob’s New Instruction Set

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The Selection Structure

• Directs the computer to repeat one or more instructions until some condition is met, at which time the computer should stop repeating the instructions

– Example: Selection structure is used every time you drive your car and approach an intersection

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The Selection Structure (continued)

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Summary

• Basic components of all algorithmic problem solutions:– Sequence

• Process instructions one after another– Selection

• Take an action based on a decision– Repetition

• Repeat a set of instructions until a condition is met

• Write simple algorithms using the sequence, selection, and repetition structures