1 / 73

Programming with Microsoft Visual Basic 2010 5 th Edition

Programming with Microsoft Visual Basic 2010 5 th Edition. Chapter Four The Selection Structure. Previewing the Monthly Payment Calculator Application. The Monthly Payment Calculator application uses the selection structure. Figure 4-1 Message box. Figure 4-2

Download Presentation

Programming with Microsoft Visual Basic 2010 5 th Edition

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Programming with Microsoft Visual Basic 2010 5th Edition Chapter Four The Selection Structure

  2. Previewing the Monthly Payment Calculator Application • The Monthly Payment Calculator application uses the selection structure

  3. Figure 4-1 Message box Figure 4-2 Monthly payment amount shown in the interface

  4. Lesson A Objectives After studying Lesson A, you should be able to: • Write pseudocode for the selection structure • Create a flowchart to help you plan an application’s code • Write an If...Then...Else statement • Include comparison operators and logical operators in a selection structure’s condition • Change the case of a string • Determine the success of the TryParse method

  5. Making Decisions in a Program • Three basic control structures • Sequence • Selection • Repetition • All procedures in an application are written using one of more of these structures • Procedures in previous chapters used sequence structure only

  6. Making Decisions in a Program (cont’d.) • Selection structure • Chooses one of two paths based on condition • Also called a decision structure • Example: • If employee works over 40 hours, add overtime pay • Condition • Decision expression evaluating to true or false

  7. Making Decisions in a Program (cont’d.) • Single-alternative selection structure • Tasks performed only when condition is true • Dual-alternative selection structure • One set of tasks performed if condition is true • Called true path • Different set of tasks performed if condition is false • Called false path • If and end if • Denotes selection structure’s beginning and end • Else denotes beginning of false path

  8. Making Decisions in a Program (cont’d.) Figure 4-3 Selection structures you might use today

  9. Making Decisions in a Program (cont’d.) • Example: Kanton Boutique Figure 4-4 Problem specification for Kanton Boutique

  10. Figure 4-5 Interface for the Kanton Boutique application Figure 4-6 Pseudocode containing only the sequence structure

  11. Figure 4-7 Modified problem specification and pseudocode containing a single-alternative selection structure

  12. Making Decisions in a Program (cont’d.) • Decision symbol • Diamond shape in a flowchart • Represents the selection structure’s condition • Other symbols • Oval: Start/stop symbol • Rectangle: Process symbol • Parallelogram: Input/output symbol

  13. Figure 4-8 Single-alternative selection structure shown in a flowchart

  14. Figure 4-9 Modified problem specification and pseudocode containing a dual-alternative selection structure

  15. Figure 4-10 Dual-alternative selection structure shown in a flowchart

  16. Coding Single-Alternative and Dual-Alternative Selection Structures • If…Then…Else statement • Used to code single and dual-alternative selection structures • Statement block • Set of statements in each path • Syntax and examples shown in Figure 4-11 on next slide

  17. Figure 4-11 Syntax and examples of the If…Then…Else statement (continues)

  18. Figure 4-11 Syntax and examples of the If…Then…Else statement (cont’d.)

  19. Comparison Operators • Comparison operators • Used to compare two values • Always result in a True or False value • Rules for comparison operators • They do not have an order of precedence • They are evaluated from left to right • They are evaluated after any arithmetic operators in the expression

  20. Figure 4-12 Listing and examples of commonly used comparison operators

  21. Comparison Operators (cont’d.) • Using comparison operators: Swapping numeric values • Sample application displays the lowest and highest of two numbers entered by the user Figure 4-14 Sample run of the Lowest and Highest application

  22. Comparison Operators (cont’d.) Figure 4-15 Pseudocode containing a single-alternative selection structure

  23. Figure 4-16 Flowchart containing a single-alternative selection structure

  24. Figure 4-17 Display button’s Click event procedure

  25. Comparison Operators (cont’d.) • Values input by the user are stored in variables with procedure scope • A temporary variable is used when values must be swapped • Declared within statement block • Block-level variable • Block scope • Restricts use of variable to statement block in which it is declared

  26. Comparison Operators (cont’d.) Figure 4-18 Illustration of the swapping concept

  27. Comparison Operators (cont’d.) • Using comparison operators: Displaying the sum or difference • Sample application displays the sum or difference of two numbers entered by the user Figure 4-19 Sample run of the Addition and Subtraction application

  28. Comparison Operators (cont’d.) Figure 4-20 Pseudocode containing a dual-alternative selection structure

  29. Figure 4-21 Pseudocode containing a dual-alternative selection structure

  30. Figure 4-22 Calculate button’s Click event procedure

  31. Logical Operators • Logical operators • Used to create compound conditions • Expressions evaluate to a Boolean value • True or False • Six logical operators in Visual Basic • Not, And, AndAlso, Or, OrElse, Xor

  32. Figure 4-23 Listing and examples of logical operators (continues)

  33. Figure 4-23 Listing and examples of logical operators (cont’d.)

  34. Logical Operators (cont’d.) • Truth tables • Show how logical operators are evaluated • Short-circuit evaluation • Bypasses evaluation of condition when outcome can be determined without it • Operators using technique: AndAlso, OrElse • Example: • If state = "TN" AndAlso sales > $5000 Then… • If state is not TN, no need to evaluate sales > $5000

  35. Figure 4-24 Truth tables for the logical operators

  36. Logical Operators (cont’d.) • Using the truth tables • Scenario: Calculate a bonus for a salesperson • Bonus condition: “A” rating and sales > $9,000 • Appropriate operators: And, AndAlso (more efficient) • Both conditions must be true to receive bonus • Sample code: strRating = "A”AndAlsodblSales> 9000

  37. Logical Operators (cont’d.) • Using logical operators: Calculating gross pay • Scenario: Calculate and display employee gross pay • Requirements for application • Verify hours are within range (>= 0.0 and <= 40.0) • If data is valid, calculate and display gross pay • If data is not valid, display error message • Can accomplish this using AndAlso or OrElse • Data validation • Verifying that input data is within expected range

  38. Comparing Strings Containing Letters • Scenario: • Display “Pass” if ‘P’ is entered in txtLetter control • Display “Fail” if ‘F’ is entered in txtLetter control • Can use the OrElse or the AndAlso operator • Note that ‘P’ is not the same as ‘p’ • They have different Unicode values

  39. Figure 4-28 Examples of using string comparisons in a procedure

  40. Converting a String to Uppercase or Lowercase • String comparisons are case sensitive • CharacterCasing property: • Three case values: Normal (default), Upper, Lower • ToUpper method: Converts string to uppercase • ToLower method: Converts string to lowercase • Syntax and examples shown in Figure 4-29 on next two slides

  41. Figure 4-29 Syntax and examples of the ToUpper and ToLower methods (continues)

  42. Figure 4-29 Syntax and examples of the ToUpper and ToLower methods (cont’d.)

  43. Converting a String to Uppercase or Lowercase (cont’d.) • Using the ToUpper and ToLower Methods: Displaying a Message • Procedure requirements • Display message “We have a store in this state” • Valid states: IL, IN, KY • Must handle case variations in the user’s input • Can use ToLower or ToUpper • Can assign a String variable to the input text box’s value converted to uppercase

  44. Figure 4-29 Examples of using the ToUpper and ToLower methods in a procedure

  45. Comparing Boolean Values • Boolean variable: Contains either True or False • Naming convention: “Is” denotes Boolean type • Example: blnIsInsured • When testing for a True value, it is not necessary to include the “= True” • Examples in Figure 4-32 on next slide

  46. Comparing Boolean Values (cont’d.) Figure 4-32 Examples of using Boolean values in a condition

  47. Comparing Boolean Values (cont’d.) • Comparing Boolean values: Determining whether a string can be converted to a number • TryParse method returns a numeric value after converting the string, or 0 if it cannot be converted • TryParse also returns a Boolean value indicating success or failure of the conversion attempt • Use Boolean value returned by TryParse method in an If…Then…Else statement

  48. Figure 4-33 Syntax and example of using the Boolean value returned by the TryParse method

  49. Summary of Operators • Precedence of logical operators • Evaluated after any arithmetic or comparison operators in the expression • Summary listing of arithmetic, concatenation, comparison, and logical operators in Figure 4-36 in text

  50. Lesson A Summary • Single and dual-alternative selection structures • Use If...Then...Else statement • Use comparison operators to compare two values • Use a temporary variable to swap values contained in two variables • Use logical operators to create a compound condition • Use text box’s CharacterCasing property to change text to upper- or lowercase

More Related