Microsoft Visual Basic 2008: Reloaded Fourth Edition

1. Microsoft Visual Basic 2008: Reloaded Fourth Edition Chapter Four Making Decisions in a Program

2. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 2 Objectives After studying this chapter, you should be able to: Include the selection structure in pseudocode and in a flowchart Explain the difference between single-alternative and dual-alternative selection structures Code a selection structure using the If…Then…Else statement Include comparison operators and logical operators in a selection structure’s condition Create a block-level variable

3. Objectives (cont'd.) Concatenate strings Use the ControlChars.NewLine constant Change the case of a string Include a check box in an interface Generate random numbers Microsoft Visual Basic 2010: Reloaded, Fourth Edition 3

4. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 4 The Selection Structure Selection structure (or decision structure): Used to select a path to take based on the outcome of a decision or comparison Condition: The decision to be made Results in a Boolean (True or False) answer Single-alternative selection structure: performs a set of tasks only when the condition is true True path: the tasks to perform when the condition is true

5. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 5 The Selection Structure (cont’d.) Dual-alternative selection structure: contains one set of tasks to perform when the condition is true and a different set of tasks to perform when the condition is false False path: the tasks to perform when the condition is false Pseudocode uses if…end if to denote a selection structure and else to denote the false path Indent instructions within the selection structure

6. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 6 The Selection Structure (cont'd.)

7. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 7 The Selection Structure (cont'd.)

8. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 8 The Selection Structure (cont'd.)

9. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 9 The Selection Structure (cont'd.)

10. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 10 The Selection Structure (cont'd.)

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14. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 14 Coding Single-Alternative and Dual-Alternative Selection Structures If…Then…Else statement: used to code single-alternative and dual-alternative selection structures Else clause: an optional part of the If statement Only used for the dual-alternative selection structure Condition must be a Boolean expression that evaluates to either True or False Can contain variables, literal constants, named constants, properties, methods, arithmetic operators, comparison operators, and logical operators Statement block: set of statements in the true path or the false path

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17. Comparison Operators Comparison operators (or relational operators): Used as part of the condition in an If…Then…Else statement to compare two values Most commonly used comparison operators: Equal to: = Greater than: > Greater than or equal to: >= Less than: < Less than or equal to: <= Not equal to: <> Microsoft Visual Basic 2010: Reloaded, Fourth Edition 17

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19. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 19 Comparison Operators (cont’d.)

20. Comparison Operators (cont'd.) Comparison operators: Have no order of precedence Are evaluated from left to right in an expression Are evaluated after any arithmetic operators in the expression All expressions containing comparison operators evaluate to True or False only Microsoft Visual Basic 2010: Reloaded, Fourth Edition 20

21. Comparison Operators (cont'd.) Microsoft Visual Basic 2010: Reloaded, Fourth Edition 21

22. Comparing Numeric Values Auction House application displays highest and lowest of two bids entered by the user Microsoft Visual Basic 2010: Reloaded, Fourth Edition 22

23. Comparing Numeric Values (cont'd.) Microsoft Visual Basic 2010: Reloaded, Fourth Edition 23

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25. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 25 Comparing Numeric Values (cont'd.)

26. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 26 Comparing Numeric Values (cont'd.)

27. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 27 Comparing Numeric Values (cont'd.)

28. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 28 Comparing Numeric Values (cont'd.)

29. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 29 Comparing Numeric Values (cont'd.)

30. Comparing Strings Addition and Subtraction Calculator application: displays the sum or difference of two numbers Microsoft Visual Basic 2010: Reloaded, Fourth Edition 30

31. Comparing Strings (cont'd.) Microsoft Visual Basic 2010: Reloaded, Fourth Edition 31

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33. Comparing Strings (cont'd.) MaxLength property: text box property that specifies the maximum number of characters that can be entered CharacterCasing property: text box property that indicates if text should remain as typed or be converted to uppercase or lowercase Microsoft Visual Basic 2010: Reloaded, Fourth Edition 33

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35. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 35 The ToUpper and ToLower Methods String comparisons in Visual Basic are case-sensitive ToUpper method: converts a string to uppercase ToLower method: converts a string to lowercase ToUpper and ToLower can be used to permanently or temporarily convert a variable’s contents

36. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 36 The ToUpper and ToLower Methods (cont’d.)

37. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 37 The ToUpper and ToLower Methods (cont’d.)

38. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 38 The ToUpper and ToLower Methods (cont’d.)

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41. Comparing Boolean Values Check boxes: used to offer the user one or more independent and nonexclusive items from which to choose Microsoft Visual Basic 2010: Reloaded, Fourth Edition 41

42. Comparing Boolean Values (cont’d.) Microsoft Visual Basic 2010: Reloaded, Fourth Edition 42

43. Comparing Boolean Values (cont’d.) Microsoft Visual Basic 2010: Reloaded, Fourth Edition 43

44. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 44 Logical Operators Logical operators (or Boolean operators): Used to combine two or more conditions into one compound condition Compound condition: a combination of conditions using logical operator(s)

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48. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 48 Logical Operators (cont'd.) Truth tables: used to evaluate logical operators in an expression Short-circuit evaluation: an evaluation in which the second condition may not be evaluated AndAlso evaluates to True only when both sub-conditions are True OrElse evaluates to False only when both sub-conditions are False AndAlso and OrElse operations do not evaluate the second condition if the first condition is false

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50. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 50 Using the Truth Tables Use And or AndAlso when both conditions must be true to give a true result Use Or or OrElse when one or both conditions must be true to give a true result Remember: logical operators are evaluated after arithmetic or comparison operators in an expression

51. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 51 The Carroll Company Application Data validation: Process of verifying that the input data is within the expected range

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53. The Carroll Company Application (cont'd.) Microsoft Visual Basic 2010: Reloaded, Fourth Edition 53

54. Summary of Operators Microsoft Visual Basic 2010: Reloaded, Fourth Edition 54

55. Summary of Operators (cont’d.) Microsoft Visual Basic 2010: Reloaded, Fourth Edition 55

56. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 56 Generating Random Integers Pseudo-random number generator: a device that produces a sequence of numbers that meets certain statistical requirements for randomness Random object: represents a pseudo-random number generator Random.Next method: Generates a random integer Can specify a minimum and maximum value

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58. Generating Random Integers (cont'd.) Microsoft Visual Basic 2010: Reloaded, Fourth Edition 58

59. Generating Random Integers (cont'd.) Microsoft Visual Basic 2010: Reloaded, Fourth Edition 59

60. Programming Tutorial 1 Microsoft Visual Basic 2010: Reloaded, Fourth Edition 60

61. Programming Tutorial 2 Microsoft Visual Basic 2010: Reloaded, Fourth Edition 61

62. Programming Example Microsoft Visual Basic 2010: Reloaded, Fourth Edition 62

63. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 63 Summary Selection structure allows a procedure to make a decision and then take the appropriate action Three types of selection structures: single-alternative, dual-alternative, and multiple-alternative Diamond symbol represents a decision in a flowchart Expressions with comparison operators will result in an answer of True or False Comparison operators are evaluated from left to right in expressions, after arithmetic operators

64. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 64 Summary (cont'd.) Variables declared within a selection expression have block-level scope Concatenation: connecting or linking two strings together with the concatenation operator (&) ControlChars.Newline advances the insertion point to the next line in a control String comparisons are case-sensitive Use ToUpper and ToLower methods to temporarily convert the case of a string

65. Microsoft Visual Basic 2010: Reloaded, Fourth Edition 65 Summary (cont'd.) Use check boxes to provide the user with one or more independent and nonexclusive choices Use logical operators to create compound conditions An expression containing a logical operator will evaluate to either True or False Logical operators have an order of precedence and are evaluated after arithmetic and comparison operators Use the pseudo-random number generator to generate random numbers