Solutions Manual Internet and World Wide Web How to Program 5th Edition Deitel

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8

JavaScript: Control

Statements II, Solutions

Who can control his fate?

—William Shakespeare

Not everything that can be

counted counts, and not every

thing that counts can be

counted.

—Albert Einstein

Self-Review Exercises

8.1 State whether each of the

following is true or false. If false,

ex-plain why.

a) The

default

case is

re-quired in the

switch

selection statement.

O b j e c t i v e s

In this chapter you’ll:

■

Learn the essentials of

counter-controlled repetition

■

Use the

for

and

do

…

while

repetition statements to

execute statements in a

program repeatedly.

■

Perform multiple selection

using the

switch

selection

statement.

■

Use the

break

and

continue

program-control

statements

■

Use the logical operators to

make decisions.

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ANS:

False. The

default

case is optional. If no

default

action is needed, then there’s no

need for a default case.

b) The

break

statement is required in the last case of a

switch

selection statement.

ANS:

False. The

break

statement is used to exit the

switch

selection statement. The

break

statement is not required for the last

case

in a

switch

selection statement.

c) The expression

( x > y && a < b )

is true if either

x > y

is true or

a < b

is true.

ANS:

False. Both of the relational expressions must be true for the entire expression to be

true when using the

&&

operator.

d) An expression containing the

||

operator is true if either or both of its operands is true.

ANS:

True.

8.2 Write a JavaScript statement or a set of statements to accomplish each of the following tasks:

a) Sum the odd integers between 1 and 99. Use a

for

structure. Assume that the variables

sum

and

count

have been declared.

ANS: sum = 0;

for

( count = 1; count <= 99; count += 2 ) sum += count;

b) Calculate the value of 2.5 raised to the power of 3. Use the

pow

method.

ANS: Math.pow( 2

.

5, 3 )

c) Print the integers from 1 to 20 by using a

while

loop and the counter variable

x

. Assume

that the variable

x

has been declared, but not initialized. Print only five integers per line.

[Hint: Use the calculation

x % 5

. When the value of this expression is

0

, start a new

paragraph in the HTML5 document.]

ANS: x = 1; document.writeln( "<p>" ); for ( x = 1; x <= 20; x++ ) { document.write( x + " " ); if ( x % 5 == 0 ) document.write( "</p><p>" ); } document.writeln( "</p>" );

d) Repeat Exercise 8.2 (c), but using a

for

statement.

ANS: document.writeln( "<p>" ); for ( x = 1; x <= 20; x++ ) { document.write( x + " " ); if ( x % 5 == 0 ) document.write( "</p><p>" ); } document.writeln( "</p>" );

8.3 Find the error in each of the following code segments, and explain how to correct it:

a) x = 1;

while ( x <= 10 ); ++x;

}

ANS:

Error: The semicolon after the

while

header causes an infinite loop, and there’s a

missing left brace.

Correction: Replace the semicolon with a

{

, or remove both the

;

and the

}

.

b)

switch ( n )

{

case 1:

document.writeln( "The number is 1" ); case 2:

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document.writeln( "The number is 2" ); break;

default:

document.writeln( "The number is not 1 or 2" ); break;

}

ANS:

Error: Missing

break

statement in the statements for the first case.

Correction: Add a

break

statement at the end of the statements for the first case. Note

that this missing statement is not necessarily an error if you want the statement of

case 2:

to execute every time the

case 1:

statement executes.

c) The following code should print the values from 1 to 10:

n = 1;

while ( n < 10 )

document.writeln( n++ );

ANS:

Error: Improper relational operator used in the

while

repetition-continuation

condi-tion.

Correction: Use

<=

rather than

<

, or change

10

to

11

.

Exercises

8.4 Find the error in each of the following segments of code [Note: There may be more than

one error]:

a)

For ( x = 100, x >= 1, ++x ) document.writeln( x );

ANS:

Error:

For

should be lowercase to be recognized, and the statements need to be

sep-arated by semicolons. Also, this code will result in an infinite loop, since

++x

will

con-tinue to increment

x

, and it will never fail to fulfill the condition

x >= 1

.

Correction: Change

For

to lowercase, replace every

,

with

;

and change

++x

to

--x

or switch the locations of the

100

and the

1 and the >=

to a

<=

.

b) The following code should print whether the integer value is odd or even:

switch ( value % 2 )

{

case 0:

document.writeln( "Even integer" ); case 1:

document.writeln( "Odd integer" ); }

ANS:

Error: There should be

break

statements for eacb case. Currently, both statements

will be executed for

case 0

.

Correction: Add a

break

statement after the content in each

case

.

c) The following code should output the odd integers from 19 to 1:

for ( x = 19; x >= 1; x += 2 ) document.writeln( x );

ANS:

Error: The code results in an infinite loop, since

x

will never be less than 1 if it starts

at 19 and always increments.

Correction: The

+=

statement should be replaced with

-=

.

d) The following code should output the even integers from 2 to 100:

counter = 2; do

{

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counter += 2;

} While ( counter < 100 );

ANS:

Error: The

While

statement should be lowercase, and the statement inside the

while

does not include the final case (where

counter = 100

).

Correction: Change

while

to lowercase, and make the conditional statement

counter <= 100

or

counter < 101

.

8.5 What does the following script do?

ANS:

8.6 Write a script that finds the smallest of several non-negative integers. Assume that the first

value read specifies the number of values to be input from the user.

1 <!DOCTYPE html>

2

3  4 <html>

5 <head>

6 <meta charset = "utf-8">

7 <title>Mystery</title> 8 <script>

9

10 document.writeln( "<table>" );

11

12 for ( var i = 1; i <= 7; i++ )

13 { 14 document.writeln( "<tr>" ); 15 16 for ( var j = 1; j <= 5; j++ ) 17 document.writeln( "<td>(" + i + ", " + j + ")</td>" ); 18 19 document.writeln( "</tr>" ); 20 } // end for 21 22 document.writeln( "</table>" ); 23 24 </script> 25 </head><body /> 26 </html>

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ANS:

1

<!DOCTYPE html>

2

3

4

<html>

5

<head>

6

<meta charset = "utf-8">

7

<title>Solution 8.6</title>

8

<script>

9

10

var i;

11

var input;

12

var amount;

13

var current;

14

var smallest;

15

16

input = parseInt( window.prompt( "How many numbers?", "0" ) );

17

amount = parseInt( input );

18

19

if ( input !== 0 )

20

{

21

input = window.prompt( "Enter first integer:", "0" );

22

smallest = parseInt( input );

23

document.writeln( "Number entered: " + smallest );

24

} // end if

25

26

for ( i = 2 ; i <= amount ; i++ )

27

{

28

input = window.prompt( "Enter next integer", "0" );

29

current = parseInt( input );

30

document.writeln( "<br />Number entered: " + current );

31

32

if ( current < smallest )

33

smallest = current;

34

} // end for

35

document.writeln( "<p>Smallest number is: " +

36

smallest + "</p>" );

37

38

</script>

39

</head><body></body>

40

</html>

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8.7 Write a script that calculates the product of the odd integers from 1 to 15 and outputs

HTML5 text that displays the results.

ANS:

1

<!DOCTYPE html>

2

3

4

<html>

5

<head>

6

7

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8.8 Modify the compound interest program in Fig. 8.6 to repeat its steps for interest rates of 5,

6, 7, 8, 9 and 10 percent. Use a

for

statement to vary the interest rate. Use a separate table for each

rate.

ANS:

8

<script>

9

10

var result = 1;

11

12

for ( var i = 1; i <= 15; i += 2 )

13

result *= i;

14

15

document.writeln( "<h2>Solution 8.7</h2>" );

16

document.writeln( "Result = " + result );

17

18

</script>

19

20

</html>

1

<!DOCTYPE html>

2

3

4

<html>

5

<head>

6

7

8

<style type = "text/css">

9

table { width: 300px;

10

border-collapse: collapse;

11

background-color: lightblue;

12

margin: 10px;}

13

table, td, th { border: 1px solid black;

14

padding: 4px; }

15

th { text-align: left;

16

color: white;

17

background-color: darkblue; }

18

tr.oddrow { background-color: white; }

19

</style>

20

<script>

21

22

var principal = 1000.0;

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24

for ( var interestRate = 5; interestRate <= 10; interestRate++ )

25

{

26

document.writeln( "<table>" );

27

document.writeln( "<tr><th>Year</th>" );

28

document.writeln( "<th>Amount on deposit</th>" );

29

document.writeln( "<th>Interest Rate</th></tr>" );

30

31

var rate = interestRate / 100.0;

32

33

for ( var year = 1; year <= 10; year++ )

34

{

35

var amount = principal * Math.pow( 1.0 + rate, year );

36

37

if ( year % 2 !== 0 )

38

document.writeln( "<tr class='oddrow'><td>" + year +

39

"</td><td>" + amount.toFixed( 2 ) + "</td><td>" +

40

rate + "</td></tr>" );

41

else

42

document.writeln( "<tr><td>" + year +

43

"</td><td>" + amount.toFixed( 2 ) + "</td><td>" +

44

rate + "</td></tr>" );

45

} // end for

46

47

document.writeln( "</table>" );

48

} // end for

49

50

</script>

51

52

</html>

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8.9 One interesting application of computers is drawing graphs and bar charts (sometimes

called histograms). Write a script that reads five numbers between 1 and 30. For each number read,

output HTML5 text that displays a line containing that number of adjacent asterisks. For example,

if your program reads the number 7, it should output HTML5 text that displays *******.

ANS:

1

<!DOCTYPE html>

2

3

4

<html>

5

<head>

6

7

8

<script>

9

10

var input;

11

var number;

12

13

for ( var i = 1; i <= 5; ++i )

14

{

15

input = window.prompt( "Enter a number: ", "0" );

16

number = parseInt( input );

17

18

while ( number < 1 || number > 30 )

19

{

20

input = window.prompt( "Input not in range. " +

21

"Enter a number: ", "0" );

22

number = parseInt( input );

23

}

24

25

document.writeln( "<p>" );

26

27

for ( var stars = 1; stars <= number; ++stars )

28

document.write( "*" );

29

30

document.writeln( "</p>" );

31

} // end for

32

33

</script>

34

35

</html>

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8.10 ("The Twelve Days of Christmas” Song) Write a script that uses repetition and a

switch

struc-tures to print the song “The Twelve Days of Christmas.” You can find the words at the site

www.santas.net/twelvedaysofchristmas.htm ANS:

1

<!DOCTYPE html>

2

3

4

<html>

5

<head>

6

7

8

<style type = "text/css">

9

p { margin-top: 0;

10

margin-bottom: 0; }

11

p.firstline { margin-top: 20px; }

12

</style>

13

<script>

14

15

document.writeln( "<h1>The Twelve Days of Christmas</h1>" );

16

17

for ( var day = 1; day <= 12; ++day )

18

{

19

document.write( "<p class='firstline'>On the " );

20

21

switch ( day )

22

{

23

case 1:

24

document.write( "first" );

25

break;

26

case 2:

27

document.write( "second" );

28

break;

29

case 3:

30

document.write( "third" );

31

break;

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32

case 4:

33

document.write( "fourth" );

34

break;

35

case 5:

36

document.write( "fifth" );

37

break;

38

case 6:

39

document.write( "sixth" );

40

break;

41

case 7:

42

document.write( "seventh" );

43

break;

44

case 8:

45

document.write( "eighth" );

46

break;

47

case 9:

48

document.write( "ninth" );

49

break;

50

case 10:

51

document.write( "tenth" );

52

break;

53

case 11:

54

document.write( "eleventh" );

55

break;

56

case 12:

57

document.write( "twelfth" );

58

break;

59

} // end switch

60

61

document.writeln(

62

" day of Christmas,</p><p>my true love gave to me:</p>" );

63

64

// display remainder of verse

65

switch ( day )

66

{

67

case 12:

68

document.writeln( "<p>Twelve drummers drumming,</p>" );

69

70

case 11:

71

document.writeln( "<p>Eleven pipers piping,</p>" );

72

73

case 10:

74

document.writeln( "<p>Ten lords-a-leaping,</p>" );

75

76

case 9:

77

document.writeln( "<p>Nine ladies dancing,</p>" );

78

79

case 8:

80

document.writeln( "<p>Eight maids-a-milking,</p>" );

81

82

case 7:

83

document.writeln( "<p>Seven swans-a-swimming,</p>" );

84

85

case 6:

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87

88

case 5:

89

document.writeln( "<p>Five golden rings.</p>" );

90

91

case 4:

92

document.writeln( "<p>Four calling birds,</p>" );

93

94

case 3:

95

document.writeln( "<p>Three French hens,</p>" );

96

97

case 2:

98

document.writeln( "<p>Two turtle doves, and</p>" );

99

100

case 1:

101

document.writeln( "<p>a Partridge in a pear tree.</p>");

102

} // end switch

103

} // end for

104

//-->

105

</script>

106

107

</html>

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8.11 A mail-order house sells five different products whose retail prices are as follows: product 1,

$2.98; product 2, $4.50; product 3, $9.98; product 4, $4.49; and product 5, $6.87. Write a script

that reads a series of pairs of numbers as follows:

a) Product number

b) Quantity sold for one day

Your program should use a

switch

statement to help determine the retail price for each product

and should calculate and output HTML5 that displays the total retail value of all the products sold

last week. Use a

prompt

dialog to obtain the product number and quantity from the user. Use a

sen-tinel-controlled loop to determine when the program should stop looping and display the final

results.

ANS:

1

<!DOCTYPE html>

2

3

4

<html>

5

<head>

6

7

<style type = "text/css">

8

table { width: 100% }

9

th { text-align: left }

10

</style>

11

12

<script>

13

14

var product1 = 0;

15

16

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17

18

19

var inputString;

20

var productId = 1;

21

22

while ( productId != 0 )

23

{

24

inputString = window.prompt(

25

"Enter product number ( 1-5 ) ( 0 to stop ):" );

26

productId = parseInt( inputString );

27

28

if ( productId >= 1 && productId <= 5 )

29

{

30

inputString = window.prompt(

31

"Enter quantity sold:" );

32

var quantity = parseInt( inputString );

33

34

switch ( productId )

35

{

36

case 1:

37

product1 += quantity * 2.98;

38

break;

39

case 2:

40

41

break;

42

case 3:

43

44

break;

45

case 4:

46

47

break;

48

case 5:

49

50

break;

51

} // end switch

52

} // end if

53

else if ( productId != 0 )

54

{

55

window.alert(

56

"Product number must be between 1 and 5 or "

57

+ "0 to stop" );

58

} //end else if

59

} // end while

60

61

document.writeln( "<h2>Product Totals</h2>" );

62

document.writeln( "<table border = '1'>" );

63

document.writeln( "<tr><th>Product #</th>" );

64

document.writeln( "<th>Total Sales</th></tr>" );

65

document.writeln( "<tr><td> Product 1 </td><td>"

66

+ product1 + "</td>" + "<tr><td> Product 2 </td><td>"

67

+ product2 + "</td></tr>" + "<tr><td> Product 3 </td><td>"

68

69

70

+ product5 + "</td></tr></table>" );

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71

72

</script>

73

74

</html>

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8.12 Assume

i = 1

,

j = 2

,

k = 3

and

m = 2

. What does each of the following statements print?

Are the parentheses necessary in each case?

a)

document.writeln( i == 1 ); ANS: true

b)

document.writeln( j == 3 ); ANS: false

c)

document.writeln( i >= 1 && j < 4 ); ANS: true

d)

document.writeln( m <= 99 & k < m ); ANS: false

[Note: The

&

in part (d) should be

&&

.]

e)

document.writeln( j >= i || k == m ); ANS: true

f)

document.writeln( k + m < j || 3 - j >= k ); ANS: false

[Note: The

|

in part (f) should be

||.

]

g)

document.writeln( !( k > m ) );

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8.13 Given the following

switch

statement:

What values are assigned to

x

when

k

has values of 1, 2, 3, 4 and 10?

ANS: x

= 1,

x

= 3,

x

= 4,

x

= 3 and

x

= 30, respectively.

1

switch ( k )

2

{

3

case 1:

4

break;

5

case 2:

6

case 3:

7

++k;

8

break;

9

case 4:

10

--k;

11

break;

12

default:

13

k *= 3;

14

}

15

16

x = k;