chapter 5: repetition and loop statements

© 2010 Pearson Addison-Wesley. All rights reserved.

Addison Wesley is an imprint of

Chapter 5:Repetition and Loop Statements

Problem Solving & Program Design in C

Sixth Edition

By Jeri R. Hanly &

Elliot B. Koffman

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© 2010 Pearson Addison-Wesley. All rights reserved. 5-2

Introduction to Repetition Structures

A repetition structure causes a statement or set of statements to execute repeatedly

Allow a programmer to avoid duplicate code– Duplicate code makes a program large– Write a long sequence of statements is time

consuming– If part of the duplicate code has to be

corrected or changed, then the change has to be done many times

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Condition-Controlled Loops

• While Loop– While a condition is true, do some task

• Do-While Loop– Do some task, while condition is true

• Do-Until Loop– Do some task, while a condition is false (or

until it’s true)

• With all loops, be careful not to create infinite loops – always provide a way to break out

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The While Loop – pretest loopWhile condition

Statement

Statement

End While

Figure 5-1 The logic of a While loop

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Working with Modules and Loops• To run a program multiple times, modules

can be put within a loop

Figure 5-5 The main module of Program 5-3

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The Do-While Loop – posttest loop Do

Statement

Statement

While condition

Figure 5-8 Flowchart for the main module in Program 5-4

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The Do-Until Loop• Loop iterates until a condition is true, but

not all languages support this type of loop

Figure 5-10 The logic of a Do-Until loop

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Count-Controlled Loops

A count-controlled loop iterates a specific number of times

• A for loop is best used for this situationFor counterVariable = startingValue to maxValue

statement

statement

End for

• There is an Initialization, Test, and Increment expression that controls the loop

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For loops can also increment by more than one, count backwards by decrementing, or allow the user to control the number of interactions

The for loop in actionFigure 5-14 Flowchart for Program 5-8

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General loop concerns• Do not forget to initialize the loop control

variable• Do not forget to modify the loop control variable• Many loops are interchangeable, but generally

– Use while loop when loop may not have to process

– Use do while when it must process at least once

– Use for loop with specific number of iterations

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5.4 Calculating a Running Total

A running total is a sum of number

that accumulates with each iteration of a loop

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Sentinels

A sentinel is a special value that marks the end of a list of values, used as stop values for loops

How it can be done– Ask the user at the end of each loop iteration,

if there is another value to process– Ask the user at the beginning of the loop,

how many times the loop should process

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Sentinels – Controlled loop

1. Initialize sum to zero.

2. Get first Score

3. While score is not the sentinel

a. Add score to sum

b. Get the next score

#define SENTINEL -99

printf(“Enter first score (or %d to quit) “ ,SENTINEL);

scanf(“%d”, &score);

while (score != SENTINEL){

sum += score;

printf(“Enter next score (%d to quit) “, SENTINEL);

scanf(“%d”, &score);

}

printf(“\nSum of exam scores is %d\n”, sum);

printf(“Enter first score (or %d to quit) “ ,SENTINEL);

for (scanf(“%d”, &score);

score != SENTINEL;

scanf(“%d”, &score)) {

sum += score;

printf(“Enter next score (%d to quit) “, SENTINEL);

}

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Nested Loops All loops can be nested, that is, a loop inside of a loop

Figure 5-21 Flowchart for a clock simulator

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Figure 5.1 Flow Diagram of Loop Choice Process

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Figure 5.2 Program Fragment with a Loop

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Figure 5.3 Flowchart for a while Loop

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Figure 5.4 Program to Compute Company Payroll

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Figure 5.4 Program to Compute Company Payroll

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Figure 5.5 Using a for Statement in a Counting Loop

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*Multiplication Table of 9*//* Displays the 9s Table */

#include <stdio.h> /* printf, scanf definitions */#define MULT_NUM 9intmain(void){

int num, answer = 0;

/* Display 9s Table */printf("The 9's Multiplication Table \n\n");for (num = 0; num < 10; ++num) {

answer = num * MULT_NUM;printf("%d times %d = %d \n", num, MULT_NUM, answer);

}printf(" \n");return (0);

}

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/*Multiplication Tables*//* Displays all the tables */

#include <stdio.h> /* printf, scanf definitions */

intmain(void){

int num, mult_num, answer = 0;

/* Display 9s Table */printf("The Multiplication Tables \n\n");for (num = 0; num < 10; ++num) {

for(mult_num = 0; mult_num < 10; ++mult_num){answer = num * mult_num;printf("%d times %d = %d \n", num, mult_num, answer);

}printf(" \n");}printf(" \n");return (0);

}

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Figure 5.6 Comparison of Prefix and Postfix Increments

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Figure 5.7 Function to Compute Factorial

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Figure 5.8 Displaying a Celsius-to-Fahrenheit Conversion Table

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Figure 5.9 Program to Monitor Gasoline Storage Tank

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Figure 5.10 Sentinel-Controlled while Loop

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Figure 5.11 Batch Version of Sum of Exam Scores Program

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Figure 5.12 Program to Process Bald Eagle Sightings for a Year

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Figure 5.12 Program to Process Bald Eagle Sightings for a Year

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Figure 5.13 Nested Counting Loop Program

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Figure 5.14 Validating Input Using do-while Statement

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Figure 5.15 Structure Chart for Computing Solar Collecting Area Size

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Figure 5.16 Program to Approximate Solar Collecting Area Size

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chapter 5: repetition and loop statements

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