1. Chapter 10: Using Menus and Validating Input
Programming Logic and Design, Third Edition Comprehensive

2. Programming Logic and Design, Third Edition Comprehensive
Objectives
After studying Chapter 10, you should be able to:
Understand the need for interactive, menu-driven programs
Create a program that uses a single-level menu
Code modules as black boxes
Improve menu programs
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3. Programming Logic and Design, Third Edition Comprehensive
Objectives
Use a case structure to manage a menu
Create a program that uses a multilevel menu
Validate input
Understand types of data validation
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4. Using Interactive Programs
Programs for which all the data items are gathered prior to running use batch processing
Programs that depend on user input while the programs are running use interactive processing
Many computer programs cannot be run in batches
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5. Using Interactive Programs (continued)
Most programs must run interactively:
must interact with a user while they are running
Example: Ticket reservation programs for airlines and theaters must select tickets while you are interacting with them, not at the end of the month
Interactive computer programs are often called real-time applications:
run while a transaction is taking place, not at some later time
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6. Using Interactive Programs (continued)
You can refer to interactive processing as online processing:
the user’s data or requests are gathered during the execution of the program while the computer is operating
A batch processing system can be offline
you can collect data such as time cards or purchase information well ahead of the actual computer processing of the paychecks or bills
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7. Using Interactive Programs (continued)
A menu program is a common type of interactive program
the user sees a number of options on the screen and can select any one of them
For example, an educational program that drills you on elementary arithmetic skills might display three options
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8. Using Interactive Programs (continued)
The menu on the left is used in console applications:
require the user to enter a choice using the keyboard,
The menu style on the right is used in graphical user interface applications:
allow the user to use a mouse or other pointing device
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9. Using a Single-Level Menu
Suppose you want to write a program that displays a menu like the one shown previously in Figure 10-1
The program drills a student’s arithmetic skills
if the student chooses the first option, five addition problems are displayed
if the student chooses the second option, five subtraction problems are displayed
Uses a single-level menu:
user makes a selection from only one menu before using the program for its ultimate purpose—arithmetic practice
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10. Using a Single-Level Menu (continued)
Suppose you want to write a program that requires the user to enter a digit to make a menu choice
The mainline logic for an interactive menu program is not substantially different from any of the other sequential file programs you’ve seen so far in this book
You can create startUp(), looping(),and cleanUp()modules
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11. Using a Single-Level Menu (continued)
The only difference between the mainline logic in Figure 10-2 and that of other programs you have worked with lies in the main loop control question
When a program’s input data come from a data file, asking whether the input file is at the end-of- file (eof) condition is appropriate
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12. Using a Single-Level Menu (continued)
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13. The displayMenu()Module of the Arithmetic Drill Program
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14. The looping()Module for the Arithmetic Drill Program
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15. The cleanUp()Module for the Arithmetic Drill Program
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16. Coding Modules as Black Boxes
Any steps you want can occur within the addition()and subtraction()modules
The contents of these modules do not affect the main structure of the program in any way
Programmers often refer to the code in modules such as addition()and subtraction()as existing within a black box:
the module statements are “invisible” to the rest of the program
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17. Coding Modules as Black Boxes (continued)
When programmers develop systems containing many modules, they often code “empty” black box procedures, called stubs
Figure 10-7 shows a possible addition()module
The module:
displays four addition problems one at a time
waits for the user’s response
displays a message indicating whether the user is correct
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18. The addition()Module, Version 1
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19. Coding Modules as Black Boxes (continued)
The addition()module shown in Figure 10-7 works, but it is repetitious
a basic set of statements repeats four times, changing only the actual problem values that the user should add, and the correct answer to which the user’s response is compared
A more elegant solution:
store the problem values in arrays
use a loop
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20. Coding Modules as Black Boxes (continued)
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21. Coding Modules as Black Boxes (continued)
The addition()module in Figure 10-9 is more compact and efficient than the module shown in Figure 10-7
However, it still contains flaws
A student will not want to use the addition()module more than two or three times
Every time a user executes the program, the same four addition problems are displayed
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22. The addition()Module, Version 2, Using Arrays
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23. Coding Modules as Black Boxes (continued)
Once students have solved all the addition problems, they probably will be able to provide memorized answers without practicing arithmetic skills at all
Fortunately, most programming languages provide you with built-in modules, or functions:
subroutines that automatically provide a mathematical value such as a square root, absolute value, or random number
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24. Coding Modules as Black Boxes (continued)
Figure shows an addition()module in which two random numbers, each 10 or less, are generated for each of four arithmetic problems
Using this technique,
you do not have to store values in an array
users encounter different addition problems every time they use the program
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25. The addition()Module, Version 3, Using Random Values
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26. Making Improvements to a Menu Program
In programming, there is a saying that no program is every really completed - you always can continue to make improvements
For example, the looping()module in Figure shows that a helpful message (“You must select 1, 2, or 3”) appears when the user selects an inappropriate option
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27. Making Improvements to a Menu Program (continued)
However, if users do not understand the message, or simply do not stop to read the message, they might keep entering invalid data
As a user-friendly improvement to your program, you can add a counter that keeps track of a user’s invalid responses
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28. Programming Logic and Design, Third Edition Comprehensive
Adding an Error Message to the looping()Module for the Arithmetic Drill Program
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29. Using the Case Structure to Manage a Menu
The arithmetic drill program contains just three valid user options: numeric entries that represent Addition, Subtraction, or Quit
Many menus include more than three options, but the main logic of such programs is not substantially different from that in programs with only three
You just include more decisions that lead to additional subroutines
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30. Using the Case Structure to Manage a Menu (continued)
All menu-driven programs should be user-friendly:
they should make it easy for the user to make desired choices
Instead of requiring a user to type numbers to select an arithmetic drill
you can improve the menu program by allowing the user the additional option of typing the first letter of the desired option, for example A for addition
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31. Using the Case Structure to Manage a Menu (continued)
To enable the menu program to accept alphabetic characters as a variable named response, you must make sure you declare response as a character variable in the startUp()module
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32. Main Logic of Program Containing Four Optional Arithmetic Drills
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33. Using the Case Structure to Manage a Menu (continued)
Programmers often overlook the fact that computers recognize uppercase letters as being different from their lowercase counterparts
Figure shows the case structure that performs the menu option selection when the user can enter a variety of responses for each menu choice
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34. Using the Case Structure to Manage a Menu (continued)
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35. Using Multilevel Menus
Sometimes, a program requires more options than can easily fit in one menu
When you need to present the user with a large number of options, several potential problems arise:
If there are too many options to fit on the display at one time, the user might not know additional options are available
Overcrowded screen is not visually pleasing
Users become confused and frustrated when presented with too many choices
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36. Using Multilevel Menus (continued)
When you have many menu options to present, using a multilevel menu might be more effective than using a single-level menu
With a multilevel menu, the selection of a menu option leads to another menu from which the user can make further, more refined selections
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37. Using Multilevel Menus (continued)
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38. Programming Logic and Design, Third Edition Comprehensive
Flowchart and Pseudocode for startUp()Module for Multilevel Menu Program
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39. Programming Logic and Design, Third Edition Comprehensive
Flowchart and Pseudocode for displayMenu()Module for Multilevel Menu Program
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40. Programming Logic and Design, Third Edition Comprehensive
Flowchart and Pseudocode for looping()Module for Multilevel Menu Program
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41. Programming Logic and Design, Third Edition Comprehensive
Validating Input
Menu programs rely on user input to select one of several actions
Other types of programs also require a user to enter data
Users will make incorrect choices because:
they don’t understand the valid choices
they make typographical errors
To improve programs, employ defensive programming:
prepare for all possible errors before they occur
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42. Validating Input (continued)
Incorrect user entries are by far the most common source of computer errors
Validating input: checking the user’s responses to ensure they fall within acceptable bounds
Does not eliminate all program errors
The correct action to take when you find invalid data depends on the application
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43. Validating Input (continued)
If program uses data file
print a message so someone can correct the invalid data, OR
force the invalid data to a default value
Forcing a field to a value means you override incorrect data by setting the field to a specific value
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44. Validating Input (continued)
New programmers often make the following two kinds of mistakes when validating data:
They use incorrect logic to check for valid responses when there is more than one possible correct entry
They fail to account for the user making multiple invalid entries
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45. Validating Input (continued)
The logic shown in Figure intends to make sure that the user enters a Y or N
However, if you use the logic shown in Figure 10-26, all users will see the “invalid response” error message, no matter what they type
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46. Understanding Types of Data Validation
The data used within computer programs are varied
Thus, validating data requires a variety of methods
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47. Programming Logic and Design, Third Edition Comprehensive
Validating a Data Type
Some programming languages allow you to check data items to make sure they are the correct data type
Although this technique varies from language to language, you can often make a statement like the one shown in Figure 10-29
In this program segment, isNumeric represents a method call; it is used to check whether the entered employeeSalary falls within the category of numeric data
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48. Validating a Data Type (continued)
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49. Validating a Data Range
Sometimes, a user response or other data must fall within a range of values
For example, when the user enters a month, you typically require it to fall between 1 and 12, inclusive
The method you use to check for a valid range is similar to one you use to check for an exact match
you continue to prompt for and receive responses while the user’s response is out of range, as shown in Figure 10-30
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50. Validating a Data Range (continued)
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51. Validating Reasonableness and Consistency of Data
Data items can be the correct type and within range, but still be incorrect
However, there are many data items that you can check for reasonableness
If you make a purchase on May 3, 2004, then the payment cannot possibly be due prior to that date
If your ZIP code is 90201, your state of residence cannot be New York
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52. Validating Reasonableness and Consistency of Data (continued)
Each of the previous examples involves comparing two data fields for reasonableness and consistency
You should consider making as many such comparisons as possible when writing your own programs
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53. Validating Presence of Data
Sometimes, data are missing from a file, either for a reason or by accident
Many programming languages allow you to check for missing data with a statement similar to if Address is blank perform no Module()
You can place any instructions you like within the no Module(), including
forcing the field to a default value or
issuing an error message
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54. Programming Logic and Design, Third Edition Comprehensive
Summary
Programs for which all the data are gathered prior to running use batch processing
Programs that depend on user input while they are running use interactive, real-time, online processing
When you code a module as a black box, the module statements are invisible to the rest of the program
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55. Programming Logic and Design, Third Edition Comprehensive
Summary (continued)
A programmer can improve a menu program and assist the user by displaying a message when the selected response is not one of the allowable menu options
You can use the case structure to make decisions when you need to test a single variable against several possible values
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56. Programming Logic and Design, Third Edition Comprehensive
Summary (continued)
You can circumvent potential problems caused by a user’s invalid data entries by validating the user’s input
Some of the techniques you want to master include validating
data type
Range
reasonableness and consistency of data
presence of data
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