8.11 Drivers are concerned with mileage obtained by their automobiles. One
driver has kept track of several tankful of gasoline by recording the number
of miles driven and the number of gallons used for each tankful. Develop a JavaScript
program that will input the miles driven and gallons used (both as integers)
for each tankful. The program should calculate and output XHTML text that displays
the number of miles per gallon obtained for each tankful and prints the combined
number of miles per gallon obtained for all tankfuls up to this point. Use prompt
dialogs to obtain the data from the user.
Answer
8.12 Develop a JavaScript program that will determine whether a department-store customer has exceded the credit limit on a charge account. For each customer, the following facts are available:
8.13 A large company pays its salespeople on a commission basis. The salespeople receive $200 per week, plus 9% of their gross sales for that week. For example, a salesperson who sells $5000 worth of merchandise in a week receives $200 plus 9% of $5000, or a total of $650. You have been supplied with a list of items sold by each salesperson. The values of these items are as follows:
| Item | Value |
| 1 | 239.99 |
| 2 | 129.75 |
| 3 | 99.95 |
| 4 | 350.89 |
Develop a program that inputs one salesperson's item sold for last week, calculates
the salesperson's earnings and outputs XHTML text that displays the salesperson's
earnings.
Answer
8.14 Develop a JavaScript program that will determine the gross pay for each
of three employees. The company pays "straight time" for the first
40 hours worked by by each employee and pays "time and a half" for
all hours worked in excess of 40 hours. You are given a list of the employees
of the company, the number of hours each employee worked last week and the hourly
rate of each employee. Your program should input this information for each employee,
determine the employee's gross pay and output XHTML text that displays the employee's
gross pay. Use prompt dialogs to input the data.
Answer
8.15 The process of finding the largest value (i.e. the maximum of a group
of values) is used frequently in computer applications. For example, a progam
that determines the winner of a sales contest would input the number of units
sold by each salesperson. The salesperson who sells the most units wins the
contest. Write a pseudocode program and then a JavaScript program that inputs
a series of 10 single-digit numbers as characters, determines the largest of
the numbers and outputs XHTML text that displays the largest number. Your program
should use three variables as follows:
a) counter: A counter to count to 10 (i.e. to keep track of how many numbers
have been input and to determine when all 10 numbers have been processed);
b) number: The current digit input to the program;
c) largest: The largest number found so far.
Answer
8.16 Write a JavaScript program that uses looping to print the following table of values. Output the results in an XHTML table:
| N | 10*N | 100*N | 1000*N |
|---|---|---|---|
| 1 | 10 | 100 | 1000 |
| 2 | 20 | 200 | 2000 |
| 3 | 30 | 300 | 3000 |
| 4 | 40 | 400 | 4000 |
| 5 | 50 | 500 | 5000 |
8.17 Using an approach similar to that in Exercise 8.15, find the two largest
values among the 10 digits entered. [Note: You may input each number only once.]
Answer
8.18 Modify the program in Fig. 8.11 to validate its input. For every value
input, if the value entered is other than 1 or 2, keep looping until the user
enters a correct value.
Answer
8.23 Write a script that reads in the size of a side of a square and outputs
XHTML text that displays a hollow square of that size constructed of asterisks.
Use a prompt dialog to read the size from the user. Your program should work
for squares of all sides between 1 and 20.
Answer
8.24 A palindrome is a number or a text that reads the same backward or forward.
For example, each of the following five-digit integers is a palindrome: 12321,
55555, 45554 and 11611. Write a script that reads in a five-digit integer and
determines whether it is a palindrome. If the number is not five digits long,
output XHTML text that displays an alert dialog indicating the problem to the
user. When the user dismisses the alert dialog, allow the user to enter a new
value.
Answer
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *Your program may use only three output statements, one of the form
document.write("* ");
one of the form
document.write(" ");
and one of the form
document.writeln("<br />");
[Hint: Repetition structures are required in this exercise/]
Answer
8.26 Write a script that outputs XHTML text that keeps displaying in the browser
window the multiples of the integer 2, namely 2, 4, 8, 16, 32, 64, etc. Your
loop should not terminate (i.e. you should create an infinite loop). What happens
when you run this program?
Answer
8.27 A company wants to transmit data over the telephone, but it is concerned
that its phones may be tapped. All of its data are transmitted as four-digit
integers. It has asked you to write a progam that will encrypt its data so that
the data may be transmitted more securely. Your script should read a four-digit
integer entered by the user in a prompt dialog and encrypt it as follows: Replace
each digit by (the sum of that digit plus 7) modulus 10. Then swap the first
digit with the third, and swap the second digit with the fourth. Then output
XHTML text that displays the encrypted integer.
Answer
8.28 Write a program that inputs an encrypted four-digit integer (from Exercise 8.27) and decrypts it to form the original number.