Microsoft Visual Basic 2008: Reloaded Third Edition

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

2. Microsoft Visual Basic 2008: Reloaded, Third Edition 2 Objectives After studying this chapter, you should be able to: Include the selection structure in pseudocode and in a flowchart Write an If�Then�Else statement Write code that uses comparison operators and logical operators Create a variable having block scope Concatenate strings

3. Microsoft Visual Basic 2008: Reloaded, Third Edition 3 Objectives (continued) Use the ControlChars.NewLine constant Change the case of a string Generate random numbers

4. Microsoft Visual Basic 2008: Reloaded, Third 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 Four forms of selection structure: If If/Else If/ElseIf/Else Case

5. Microsoft Visual Basic 2008: Reloaded, Third Edition 5 The Selection Structure (continued)

6. Microsoft Visual Basic 2008: Reloaded, Third Edition 6 Writing Pseudocode for the If and If/Else Selection Structures If selection structure: contains one set of instructions to process when the condition is true If/Else selection structure: Contains two sets of instructions One set is processed when the condition is true The other set is processed when the condition is false True path: path to follow when condition is true False path: path to follow when condition is false

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8. Microsoft Visual Basic 2008: Reloaded, Third Edition 8 Flowcharting the If and If/Else Selection Structures Flowchart uses standardized symbols to show the steps a computer must take Selection/repetition symbol: Diamond shape Represents both selection and repetition structures One flowline entering and two flowlines leaving

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10. Microsoft Visual Basic 2008: Reloaded, Third Edition 10 Coding the If and If/Else Selection Structures If�Then�Else statement: used to code the If and If/Else selection structures Else clause: an optional part of the If statement Condition must be a Boolean expression Must evaluate to either True or False Statement block: set of statements terminated by an Else or End If If�Then�Else statement can contain variables, literal constants, named constants, properties, methods, arithmetic operators, comparison operators, and logical operators

11. Microsoft Visual Basic 2008: Reloaded, Third Edition 11 Coding the If and If/Else Selection Structures (continued)

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13. Comparison Operators Comparison operators (or relational operators): Used as part of the condition in an If statement 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 2008: Reloaded, Third Edition 13

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15. Comparison Operators (continued) 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 2008: Reloaded, Third Edition 15

16. Comparison Operators (continued) Microsoft Visual Basic 2008: Reloaded, Third Edition 16

17. Using Comparison Operators � Swapping Numeric Values Pseudocode for a procedure that displays highest and lowest of two numbers Microsoft Visual Basic 2008: Reloaded, Third Edition 17

18. Using Comparison Operators � Swapping Numeric Values (continued) Microsoft Visual Basic 2008: Reloaded, Third Edition 18

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20. Microsoft Visual Basic 2008: Reloaded, Third Edition 20 Using Comparison Operators � Swapping Numeric Values (continued)

21. Microsoft Visual Basic 2008: Reloaded, Third Edition 21 Using Comparison Operators � Swapping Numeric Values (continued)

22. Microsoft Visual Basic 2008: Reloaded, Third Edition 22 Using Comparison Operators � Swapping Numeric Values (continued)

23. Microsoft Visual Basic 2008: Reloaded, Third Edition 23 Using Comparison Operators � Swapping Numeric Values (continued)

24. Using Comparison Operators � Example 2 Pseudocode for a procedure to allow the user to display the sum or difference of two numbers: Microsoft Visual Basic 2008: Reloaded, Third Edition 24

25. Using Comparison Operators � Example 2 (continued) Microsoft Visual Basic 2008: Reloaded, Third Edition 25

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27. Microsoft Visual Basic 2008: Reloaded, Third Edition 27 Using Comparison Operators � Example 2 (continued)

28. Using Comparison Operators � Example 2 (continued) 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 upper- or lowercase Microsoft Visual Basic 2008: Reloaded, Third Edition 28

29. Microsoft Visual Basic 2008: Reloaded, Third Edition 29 Using 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

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31. Microsoft Visual Basic 2008: Reloaded, Third Edition 31 Using the ToUpper and ToLower Methods (continued)

32. Microsoft Visual Basic 2008: Reloaded, Third Edition 32 Using the ToUpper and ToLower Methods (continued)

33. Using the ToUpper and ToLower Methods (continued) Microsoft Visual Basic 2008: Reloaded, Third Edition 33

34. Microsoft Visual Basic 2008: Reloaded, Third Edition 34 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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37. Microsoft Visual Basic 2008: Reloaded, Third Edition 37 Logical Operators (continued) Truth tables: used to evaluate logical operators in an expression Short-circuit evaluation: an evaluation in which the second condition may not be evaluated And and Or operations always evaluate both conditions AndAlso and OrElse operations do not evaluate the second condition if the first condition is false

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39. Microsoft Visual Basic 2008: Reloaded, Third Edition 39 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 Use XOr when exactly one condition must be true to give a true result Logical operators are evaluated after arithmetic or comparison operators in an expression

40. Microsoft Visual Basic 2008: Reloaded, Third Edition 40 Using the Truth Tables (continued)

41. Using the Truth Tables (continued) Microsoft Visual Basic 2008: Reloaded, Third Edition 41

42. Microsoft Visual Basic 2008: Reloaded, Third Edition 42 Using Logical Operators in an If�Then�Else Statement Data validation: Process of verifying that the input data is within the expected range Use an If�Then�Else statement to validate input data

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44. Using Logical Operators in an If�Then�Else Statement (continued) Microsoft Visual Basic 2008: Reloaded, Third Edition 44

45. Microsoft Visual Basic 2008: Reloaded, Third Edition 45 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

46. Microsoft Visual Basic 2008: Reloaded, Third Edition 46 Generating Random Integers (continued)

47. Generating Random Integers (continued) Microsoft Visual Basic 2008: Reloaded, Third Edition 47

48. Generating Random Integers (continued) Microsoft Visual Basic 2008: Reloaded, Third Edition 48

49. Programming Tutorial Microsoft Visual Basic 2008: Reloaded, Third Edition 49

50. Programming Example Microsoft Visual Basic 2008: Reloaded, Third Edition 50

51. Microsoft Visual Basic 2008: Reloaded, Third Edition 51 Summary Selection structure allows a program to make a decision and then select one of two paths Four forms of selection structures: If, If/Else, If/ElseIf/Else, and Case 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

52. Microsoft Visual Basic 2008: Reloaded, Third Edition 52 Summary (continued) 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

53. Microsoft Visual Basic 2008: Reloaded, Third Edition 53 Summary (continued) 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