1. 1

2. Objectives
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
Use the line continuation character
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3. Objectives (continued)
Concatenate strings
Use the ControlChars NewLine constant
Change the case of a string
Determine whether an expression can be converted to a number
Display a message in a message box
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4. Objectives (continued)
Include a nested selection structure in pseudocode, flowchart, and code
Code an If/Elseif/Else selection structure
Include a Case selection structure in pseudocode, flowchart and code
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5. The Selection Structure
Also called decision structure
Make a comparison and choose between 2 paths depending upon the result of comparison (condition)
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6. Writing Pseudocode for the If and If/Else Selection Structures
If selection structure - 1 set of instructions which are processed if condition is true
If/Else - 2 sets of instructions – the first when condition is true, the other when condition is false
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7. Flowcharting the If and If/Else Selection Structures
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8. Coding the If and If/Else Selection Structures
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9. Coding the If and If/Else Selection Structures (continued)
Statement Block
Set of instructions in “true” path
(between keywords If and Then)
Optional set of instructions in “false” path
(between keywords Then and End If)
Any items in square brackets are optional
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10. Comparison Operators Also referred to as relational operators
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11. Comparison Operators (continued)
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12. Using Comparison Operators – Example 1
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13. Using Comparison Operators – Example 1 (continued)
Note: variable intTemp has block scope and can only be used in block in which declared
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14. Using Comparison Operators – Example 1 (continued)
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15. Using Comparison Operators – Example 1 (continued)
Line continuation character
Space followed by an underscore
Used to break up long instructions onto 2 lines
Concatenation Operator
The ampersand ( & )
Used to concatenate (connect or link) strings
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16. Using Comparison Operators – Example 1 (continued)
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17. HOW TO…
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18. Using Comparison Operators – Example 2
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19. Using Comparison Operators – Example 2 (continued)
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20. Using Comparison Operators – Example 2 (continued)
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21. Using the ToUpper and ToLower Methods
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22. Using the ToUpper and ToLower Methods (continued)
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23. Using the ToUpper and ToLower Methods (continued)
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24. Logical Operators
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25. Logical Operators (continued)
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26. Truth Tables
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27. Truth Tables (continued)
Note: short-circuit evaluation can occur with “And” operator. Both conditions will not be tested if first condition tests false
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28. Using the Truth Tables Understanding order of precedence is critical
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29. Using the Truth Tables (continued)
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30. Using Logical Operators in an If…Then…Else Statement
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31. Modifying the Skate-Away Sales Application
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32. Modifying the Skate-Away Sales Application (continued)
Modify to eliminate unwanted error message
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33. Modifying the Skate-Away Sales Application (continued)
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34. The IsNumeric Function
A predefined procedure that performs a specific task and returns a value after completing the task
IsNumeric function checks if an expression can be converted to a number
Returns Boolean true if able to convert to number
Returns Boolean false if conversion cant be made
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35. The IsNumeric Function (continued)
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36. The MessageBox.Show method
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37. The MessageBox.Show method (continued)
Arguments in the MessageBox.Show method
Text - a string containing the text to display
Caption - text displayed in title bar
Buttons - buttons to display in message box
Can be one of 6 different constants
Icon – icon displayed in title bar
Defaultbutton – button automatically selected if user presses the Enter key on keyboard
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38. The MessageBox.Show method (continued)
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39. The MessageBox.Show method (continued)
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40. HOW TO…
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41. Nested Selection Structures
When at least one side of the selection structure’s path contains another selection structure
Inner structure is referred to as “nested”
“Else” is paired up with nearest preceding If regardless of indentation of code
Use when you want to make one decision and then choose between two options depending upon the result of the first decision
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42. Nested Selection Structures (continued)
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43. Nested Selection Structures (continued)
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44. Nested Selection Structures (continued)
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45. Nested Selection Structures (continued)
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46. The If/ElseIf/Else Selection Structure
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47. The Case Selection Structure
PsuedoCode
Get Grade
Grade value:
Display “Excellent”
Display “Above Average”
Display “Average”
D,F Display “Below Average”
Other Display “Error”
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48. The Case Selection Structure (continued)
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49. HOW TO…
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50. Using To and Is in an ExpressionList
To allows range of values in Case expression
Example
Number of items ordered Price per item
$25
$23
Is allows use of comparison operators
More than $20
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51. Using To and Is in an ExpressionList (continued)
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52. Programming Example – Fat Calculator
Application allows user to enter the total number of calories and grams of fat contained in a specific food
Calculate and display 2 values: number of fat calories, and fat percentage
Display appropriate message depending on level of fat percentage
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53. TOE Chart
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54. User Interface
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55. Objects, Properties, and Settings
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56. Objects, Properties, and Settings (continued)
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57. Tab Order
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58. Pseudocode btnExit Click event procedure close application
btnCalc Click event procedure
if the txtCalories and txtFatGrams controls contain numbers
assign the numbers to variables
calculate the fat calories by multiplying total calories by 9
calculate fat percentage by dividing fat by total calories
display fat calories and fat percentage in appropriate labels
if fat percentage is over 30%
display “This food is high in fat” in message box
else
display “This food is not high in fat” in message box
end if
display “The calories and fat grams must be numbers”
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59. Code
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60. Code (continued)
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61. Summary
Selection structure allows program to make a decision and then select one of 2 paths depending upon the results of that decision
Visual Basic .NET has 4 selection structures
If If/Else
If/ElseIf/Else Case
Selection structures can be “nested” within other selection structures
Outer structure contains primary decision
Inner structure contains secondary decision
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62. Summary (continued)
All expressions in a selection structure evaluate to either true or false
Use line continuation character (space &) to break up long instruction into 2 physical lines
Use concatenation operator (&) to connect (link) 2 strings together
String comparisons are case sensitive
Use ToUpper and ToLower functions to convert case
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63. Summary (continued)
ControlChars.NewLine constant advances insertion point to the next line in a control
Use logical operators to create compound conditions (And, Or, AndAlso)
IsNumeric function verifies expression can be converted to a number
MessageBox.Show allows communication with user in the form of a message box
Use If/ElseIf/Else and Case selection structures to choose between multiple alternatives
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