Chapter 5. Looping

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Chapter 5. Looping

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Title: Chapter 1. Introduction to Computers and Programming Author: Catherine Wyman Last modified by: Tony Gaddis Created Date: 8/31/1999 9:01:44 PM – PowerPoint PPT presentation

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Title: Chapter 5. Looping

1
Chapter 5. Looping
2
5.1 The Increment and Decrement Operators

and -- are operators that add and subtract one
from their operands.
num num 1
num 1
num

3
Program 5-1

// This program demonstrates the increment and
decrement
// operators.
include ltiostream.hgt
void main(void)
int bigVal 10, smallVal 1
cout ltlt "bigVal is " ltlt bigVal
ltlt " and smallVal is " ltlt smallVal ltlt endl
smallVal
bigVal--

Program continues
4
Program continued from previous slide.

cout ltlt "bigVal is " ltlt bigVal
ltlt " and smallVal is " ltlt smallVal ltlt endl
smallVal
--bigVal
cout ltlt "bigVal is " ltlt bigVal
ltlt " and smallVal is " ltlt smallVal ltlt endl

5
Program Output

bigVal is 10 and smallVal is 1
bigVal is 9 and smallVal is 2
bigVal is 8 and smallVal is 3

6
Program 5-2

//This program demonstrates the prefix and
postfix modes of the
// increment and decrement operators.
include ltiostream.hgt
void main(void)
int bigVal 10, smallVal 1
cout ltlt "bigVal starts as " ltlt bigVal
cout ltlt " and smallVal starts as " ltlt smallVal
ltlt endl
cout ltlt "bigVal-- " ltlt bigVal-- ltlt endl
cout ltlt "smallVal " ltlt smallVal ltlt endl
cout ltlt "Now bigVal is " ltlt bigVal ltlt endl
cout ltlt "Now smallVal is " ltlt smallVal ltlt endl
cout ltlt "--bigVal " ltlt --bigVal ltlt endl
cout ltlt "smallVal " ltlt smallVal ltlt endl

7
Program Output

bigVal starts as 10 and smallVal starts as 1
bigVal-- 10
smallVal 1
Now bigVal is 9
Now smallVal is 2
--bigVal 8
smallVal 3

8
Using and -- in Mathematical Expressions

a 2
b 5
c a b
cout ltlt a ltlt ltlt b ltlt ltlt c
Results 2 6 10

9
Using and -- in Relational Expressions

x 10
if ( x gt 10)
cout ltlt x is greater than 10.\n
Two operations are happening
the value in x is tested to determine if it is
greater than 10
then x is incremented

10
5.2 Introduction to Loops - The while Loop

A loop is part of a program that repeats.
A while loop is a pre test loop - the
expression is tested before the loop is executed
while (expression)
statement

11
Program 5-3

// This program demonstrates a simple while loop.
include ltiostream.hgt
void main(void)
int number 0
cout ltlt "This program will let you enter number
after\n"
cout ltlt "number. Enter 99 when you want to quit
the "
cout ltlt "program.\n"
while (number ! 99)
cin gtgt number

12
Program Output with Example Input

This program will let you enter number after
number. Enter 99 when you want to quit the
program.
1 Enter
2 Enter
30 Enter
75 Enter
99 Enter

13
Terminating a Loop

A loop that does not have a way of stopping is
called an infinite loop
int test 0
while (test lt 10)
cout ltlt Hello\n
A null statement is also an infinite loop, but it
does nothing forever
while (test lt 10)

14
Programming Style and the while Loop

If there is only one statement repeated by the
loop, it should appear on the line after the
while statement and be indented one additional
level
If the loop repeats a block, the block should
begin on the line after the while statement and
each line inside the braces should be indented

15
5.3 Counters

A counter is a variable that is incremented or
decremented each time a loop iterates.

16
Program 5-4

// This program displays the numbers 1 through 10
and
// their squares.
include ltiostream.hgt
void main(void)
int num 1 // Initialize counter
cout ltlt "number number Squared\n"
cout ltlt "-------------------------\n"
while (num lt 10)
cout ltlt num ltlt "\t\t" ltlt (num num) ltlt endl
num // Increment counter

17
Program Output

number number Squared
-------------------------1 12
43 94
165 256 367
498 649
8110 100

18
Program 5-5

// This program displays the numbers 1 through 10
and
// their squares.
include ltiostream.hgt
void main(void)
int num 0
cout ltlt "number number Squared\n"
cout ltlt "-------------------------\n"
while (num lt 10)
cout ltlt num ltlt "\t\t" ltlt (num num) ltlt endl

19
Program Output

number number Squared
-------------------------1 12
43 94
165 256 367
498 649
8110 100

20
5.4 Letting the User Control the Loop

We can let the user indicate the number of times
a loop should repeat.

21
Program 5-6

// This program averages a set of test scores for
multiple
// students. It lets the user decide how many.
include ltiostream.hgt
void main(void)
int numStudents, count 0
cout ltlt "This program will give you the average
of three\n"
cout ltlt "test scores per student.\n"
cout ltlt "How many students do you have test
scores for? "
cin gtgt numStudents
cout ltlt "Enter the scores for each of the
students.\n"
cout.precision(2)

Program continues
22
Program continued from previous slide.

while (count lt numStudents)
int score1, score2, score3
float average
cout ltlt "\nStudent " ltlt count ltlt " "
cin gtgt score1 gtgt score2 gtgt score3
average (score1 score2 score3) / 3.0
cout ltlt "The average is " ltlt average ltlt ".\n"

23
Program Output with Example Input

This program will give you the average of three
test scores per student.
How many students do you have test scores for? 3
Enter
Enter the scores for each of the students.
Student 1 75 80 82 Enter
The average is 79.
Student 2 85 85 90 Enter
The average is 86.67.
Student 3 60 75 88 Enter
The average is 74.33.

24
5.5 Keeping a Running Total

A running total is a sum of numbers that
accumulates with each iteration of a loop. The
variable used to keep the running total is called
an accumulator.

25
Program 5-7

// This program takes daily sales figures over a
period of
// time and calculates their total.
include ltiostream.hgt
void main(void)
int days, count 0
float total 0.0
cout ltlt "For how many days do you have sales
figures? "
cin gtgt days

Program continues
26
Program continues

while (count lt days)
float sales
cout ltlt "Enter the sales for day " ltlt count ltlt
" "
cin gtgt sales
total sales
cout.precision(2)
cout.setf(iosfixed iosshowpoint)
cout ltlt "The total sales are " ltlt total ltlt
endl

27
Program Output with Example Input

For how many days do you have sales figures? 5
Enter
Enter the sales for day 1 489.32 Enter
Enter the sales for day 2 421.65 Enter
Enter the sales for day 3 497.89 Enter
Enter the sales for day 4 532.37 Enter
Enter the sales for day 5 506.92 Enter
The total sales are 2448.15

28
5.6 Sentinels

A sentinel is a special value that marks the end
of a list of values.

29
Program 5-8

// This program calculates the total number of
points a
// soccer team has earned over a series of games.
The user
// enters a series of point values, then -1 when
finished.
include ltiostream.hgt
void main(void)
int count 0, points 0, total 0
cout ltlt "Enter the number of points your team
has earned\n"
cout ltlt "so far in the season, then enter -1
when\n"
cout ltlt "finished.\n"

Program continues
30
Program continued from previous slide.

while (points ! -1)
count
cout ltlt "Enter the points for game " ltlt count
ltlt " "
cin gtgt points
if (points ! -1)
total points
cout ltlt "The total points are " ltlt total ltlt
endl

31
Program Output with Example Input

Enter the number of points your team has earned
so far in the season, then enter -1 when you are
finished.
Enter the points for game 1 7 Enter
Enter the points for game 2 9 Enter
Enter the points for game 3 4 Enter
Enter the points for game 4 6 Enter
Enter the points for game 5 8 Enter
Enter the points for game 6 -1 Enter
The total points are 34

32
5.7 The do-while Loop and for Loops

In addition to the while loop, C also offers
the do-while and for loops.
A do-while loop is similar to a while loop, but
in post-test format
do
statement
while (expression)

33
Program 5-9

//This program averages 3 test scores. It repeats
as many times as
// the user wishes
include ltiostream.hgt
void main(void)
int score1, score2, score3
float average
char again
do
cout ltlt "Enter 3 scores and I will average
them "
cin gtgt score1 gtgt score2 gtgt score3
average (score1 score2 score3) / 3.0
cout ltlt "The average is " ltlt average ltlt ".\n"
cout ltlt "Do you want to average another set?
(Y/N) "
cin gtgt again
while (again 'Y' again 'y')

34
Program Output with Example Input

Enter 3 scores and I will average them 80 90 70
Enter
The average is 80.
Do you want to average another set? (Y/N) y
Enter
Enter 3 scores and I will average them 60 75 88
Enter
The average is 74.333336.
Do you want to average another set? (Y/N) n
Enter

35
Program 5-10

// This program displays a menu and asks the user
to make a
// selection. A switch statement determines which
item the
// user has chosen. A do-while loop repeats the
program until
// the user selects item 4 from the menu.
include ltiostream.hgt
void main(void)
int choice, months
float charges
cout.setf(iosfixed iosshowpoint)
cout.precision(2)

Program continues
36
Program continued from previous slide.

do
cout ltlt "\n\t\tHealth Club Membership
Menu\n\n"
cout ltlt "1. Standard Adult Membership\n"
cout ltlt "2. Child Membership\n"
cout ltlt "3. Senior Citizen Membership\n"
cout ltlt "4. Quit the Program\n\n"
cout ltlt "Enter your choice "
cin gtgt choice
if (choice ! 4)
cout ltlt "For how many months? "
cin gtgt months

Program continues
37
Program continued from previous slide.

switch (choice)
case 1 charges months 40.00
cout ltlt "The total charges are "
cout ltlt charges ltlt endl
break
case 2 charges months 20.00
cout ltlt "The total charges are "
cout ltlt charges ltlt endl
break
case 3 charges months 30.00
cout ltlt "The total charges are "
cout ltlt charges ltlt endl
break

Program continues
38
Program continued from previous slide.

case 4 cout ltlt "Thanks for using this
" cout ltlt "program.\n" break
default cout ltlt "The valid choices are 1-4.
" cout ltlt "Try again.\n" while
(choice ! 4)

Program continues
39
Program Output with Example Input

Health Club Membership Menu 1. Standard
Adult Membership2. Child Membership3. Senior
Citizen Membership4. Quit the ProgramEnter
your choice 1 EnterFor how many months 12
EnterThe total charges are 480.00
Health Club Membership Menu 1. Standard
Adult Membership2. Child Membership3. Senior
Citizen Membership4. Quit the ProgramEnter
your choice 4 EnterThanks for using this
program.

40
The for Loop

Ideal for situations that require a counter
because it has built-in expressions that
initialize and update variables.
for (initialization test update)
statement

41
Program 5-11

// This program displays the numbers 1 through 10
and
// their squares.
include ltiostream.hgt
void main(void)
int num
cout ltlt Number Number Squared\n"
cout ltlt "-------------------------\n"
for (num 1 num lt 10 num)
cout ltlt num ltlt "\t\t" ltlt (num num) ltlt endl

42
Program Output

Number Number Squared
-------------------------1 12
43 94
165 256 367
498 649
8110 100

43
Omitting the for Loops Expressions

int num 1
for ( num lt 10 num)
cout ltlt num ltlt \t\t ltlt (num num) ltlt endl

44
Using initialization and update lists

You may need to perform more than one statement
in the initialization part of a for loop. In that
case, just separate the statements with commas.

45
Program 5-12

// This program takes daily sales figures for one
week
// and calculates their total.
include ltiostream.hgt
void main(void)
const int days 7
int count
float total
for (count 1, total 0.0 count lt days
count)
float sales
cout ltlt "Enter the sales for day " ltlt count ltlt
" "

Program continues
46
Program continued from previous slide.

cin gtgt sales
total sales
cout.precision(2)
cout.setf(iosfixed iosshowpoint)
cout ltlt "The total sales are " ltlt total ltlt
endl

47
Program Output with Example Input

Enter the sales for day 1 489.32 Enter
Enter the sales for day 2 421.65 Enter
Enter the sales for day 3 497.89 Enter
Enter the sales for day 4 532.37 Enter
Enter the sales for day 5 506.92 Enter
Enter the sales for day 6 489.01 Enter
Enter the sales for day 7 476.55 Enter
The total sales are 3413.71

48
5.8 Other forms of the update expression

Incrementing the counter by something besides 1
for(number 2 number lt 100 number 2)
cout ltlt number ltlt endl // print the even numbers
2 100
Going backwards
for(number 10 number gt 0 number--)
cout ltlt number ltlt endl //count from 10 to 0
A stand-alone for loop
//This one prints the integers from 1 to 10
for(number 1 number lt 10 cout ltlt number)
There are quite a few variations, try some of
your own!

49
5.8 Focus on Software Engineering Deciding Which
Loop to Use

The while Loop
A pre-test loop.
Use when you do not want the loop to iterate if
the condition is false from the beginning.
Ideal if you want to use a sentinel.
The do-while Loop
A post-test loop.
Use if you always want the loop to iterate at
least once.
The for Loop
A pre-test loop.
Automatically executes an update expression at
the end of each iteration.
Ideal for situations where a counter variable is
needed.
Used when the exact number of required iterations
is known.