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  1. Chapter 3 Fundamentals of Programming in Visual Basic Chapter 3 - Visual Basic Schneider

  2. Visual Basic Objects Visual Basic Events Numbers Strings Input/Output Built-In Functions Outline and Objectives Chapter 3 - Visual Basic Schneider

  3. The Initial Visual Basic Screen Menu bar Project Explorer window Toolbar Toolbox Properties window Description pane Form Project Container window Form Layout window Chapter 3 - Visual Basic Schneider

  4. Steps to Create a Visual Basic Program 1. Create the interface by placing controls on the form 2. Set properties for the controls and the form 3. Write code for event procedures associated with the controls and the form Chapter 3 - Visual Basic Schneider

  5. Four Useful Visual Basic Controls • Text Boxes • Labels • Command Buttons • Picture Boxes Chapter 3 - Visual Basic Schneider

  6. Placing a Text Box on a Form • Double-click on the text box icon in the toolbox to add a text box to your form • Activate the properties window (Press F4) • Set values of properties for text box Chapter 3 - Visual Basic Schneider

  7. Placing a Text Box on a Form Text box Chapter 3 - Visual Basic Schneider

  8. Name Caption Text (for Text Boxes) BorderStyle Visible BackColor Alignment Font Some Useful Properties of Objects Chapter 3 - Visual Basic Schneider

  9. Example Chapter 3 - Visual Basic Schneider

  10. Naming Objects: • Use the Propertywindow to change the Name property of an object • Good programming practice dictates that each object name begins with a three letter prefix that identifies the type of object. Chapter 3 - Visual Basic Schneider

  11. Naming Objects: Chapter 3 - Visual Basic Schneider

  12. Naming Objects • An Object Name • Must Start with a letter • Can include numbers and underscore (_) • Cannot include punctuation or spaces • Can be a maximum of 40 characters Chapter 3 - Visual Basic Schneider

  13. Visual Basic Events • Code is a set of statements that instruct the computer to carry out a task. • Code can be associated with events • When an event occurs, the code associated with that event (called an Event Procedure) is executed. Chapter 3 - Visual Basic Schneider

  14. Creating An Event Procedure • Double-click on an object to open a Code window. (The empty default event procedure will appear. Click on the Procedure box if you want to display a different event procedure.) • Write the code for that event procedure. Chapter 3 - Visual Basic Schneider

  15. Example of An Event Procedure Private Sub objectName_event ( ) statements End Sub Private Sub txtOne_GotFocus( ) txtOne.Font.Size = 12 txtOne.Font.Bold = False End Sub Chapter 3 - Visual Basic Schneider

  16. More Examples Private Sub cmdButton_Click( ) txtBox.ForeColor = vbRed txtBox.Font.Size = 24 txtBox.Text = “Hello” End Sub Chapter 3 - Visual Basic Schneider

  17. Exercises 11. Private Sub cmdButton_Click( ) frmHi= “Hello” End Sub 12. Private Sub cmdButton_Click( ) txtOne.ForeColor= “red” End Sub Chapter 3 - Visual Basic Schneider

  18. Exercises 13. Private Sub cmdButton_Click( ) txtBox.Caption = “Hello” End Sub 16. Private Sub cmdButton_Click( ) txtOne.MultiLine= True End Sub Chapter 3 - Visual Basic Schneider

  19. Tips • Most Properties can be set or altered at run time with code. cmdButton.visible = False • The BorderStyle and MultiLine properties of a text box can only be set from the properties window • “” surrounds Caption, Name, Font.Name or strings not True, vars or numeric constants Chapter 3 - Visual Basic Schneider

  20. Color Constants • At design time colors are selected from a palette • At run time the eight most common colors can be assigned with the color constants: Chapter 3 - Visual Basic Schneider

  21. Components of Visual Basic Statements • Constants • Variables • Keywords (reserved words) Chapter 3 - Visual Basic Schneider

  22. Constant • Can NOT change during the execution of a program. • Types of Constants: • numeric constants • string constants Chapter 3 - Visual Basic Schneider

  23. Valid Numeric Constants: IntegerReal number -2987 -1900.05 16 0.0185 5 10.56 Chapter 3 - Visual Basic Schneider

  24. Invalid Numeric Constants: 14,005.5 6.8% 33- $190.04 15 78 3.5& Chapter 3 - Visual Basic Schneider

  25. Arithmetic Operations Operator Operation Basic expression ^ Exponentiation A ^ B * Multiplication A * B / Division A / B + Addition A + B - Subtraction A - B Chapter 3 - Visual Basic Schneider

  26. Scientific Notation • Largest/Smallest number a Single can handle Chapter 3 - Visual Basic Schneider

  27. Variables • A storage location in main memory whose value can be changed during program execution. • These storage locations can be referred to by their names. • Every variable has three properties: a Name, a Value, and a Data Type. • Types of variables: Numeric and String Chapter 3 - Visual Basic Schneider

  28. Must begin with a letter Must contain only letters, numeric digits, and underscores ( _ ) Can have up to 255 characters Cannot be a Visual Basic language keyword (for example, Sub, End, False) Rules for Naming Variables Chapter 3 - Visual Basic Schneider

  29. Words that have predefined meaning to Visual Basic . Can Not be used as variable names. Examples: End - Print Sub - Let If -Select While -Call Keywords Chapter 3 - Visual Basic Schneider

  30. Used to store numbers Value is assigned by a statement of the form: numVar = expression The variable must be on the left and the expression on the right. Numeric Variables Chapter 3 - Visual Basic Schneider

  31. Assignment Statement: • The statement var = expr assigns the value of the expression to the variable • tax = 0.02 * (income - 500 * dependents) • sum = 2 + x + 4.6 + y Chapter 3 - Visual Basic Schneider

  32. timeElapsed taxRate speed n celsius Valid Numeric Variable Names: Chapter 3 - Visual Basic Schneider

  33. maximum/average 1stChoice square yard Invalid Numeric Variable Names: Chapter 3 - Visual Basic Schneider

  34. Valid Assignment Statements • count = count + 1 • num = 5 • count = count + num /2 Chapter 3 - Visual Basic Schneider

  35. 10 = count count + 1 = count Invalid Assignment Statements Chapter 3 - Visual Basic Schneider

  36. Print is a method used to display data on the screen or printer. Can be used to display values of variables or expressions Visual Basic Print Statement Chapter 3 - Visual Basic Schneider

  37. Examples of Print Statements Private Sub cmdCompute_Click() picResults.Print 3 + 2 picResults.Print 3 - 2 picResults.Print 3 * 2 picResults.Print 3 / 2 picResults.Print 3 ^ 2 picResults.Print 2 * (3 + 4) End Sub Chapter 3 - Visual Basic Schneider

  38. picOutput.Print speed picOutput.Print taxRate picOutput.Print “Class average is”; total / 3 Examples of Print Statements Chapter 3 - Visual Basic Schneider

  39. x = 15 y = 5 picOutput.Print (x + y) / 2, x / y Output: 10 3 Examples of Print Statements Chapter 3 - Visual Basic Schneider

  40. String Constants: • A sequence of characters treated as a single item • The characters in a string must be surrounded by double quotes (“ ”) Chapter 3 - Visual Basic Schneider

  41. Valid String Constants “A rose by any other name” “9W” “134.23” “She said, ‘stop , thief!’ ” Chapter 3 - Visual Basic Schneider

  42. Invalid String Constants ‘Down by the Seashore’ “134.24 “She said, “Stop, thief!”” Chapter 3 - Visual Basic Schneider

  43. A string variable stores a string. The rules for naming string variables are identical to those for naming numeric variables. When a string variable is first declared, its value is the empty string. String Variables Chapter 3 - Visual Basic Schneider

  44. Private Sub cmdShow_Click() picOutput.Cls phrase = "win or lose that counts." picOutput.Print "It's not whether you "; phrase picOutput.Print "It's whether I "; phrase End Sub String Variable Example Chapter 3 - Visual Basic Schneider

  45. Two strings can be combined by using the concatenation operation. The concatenation operator is the ampersand (&) sign. Concatenation Chapter 3 - Visual Basic Schneider

  46. strVar1 = “Hello”strVar2 = “World”picOutput.Print strVar1& strVar2 txtBox.Text = “32” & Chr(176) & “ Fahrenheit” Examples of Concatenation: Chapter 3 - Visual Basic Schneider

  47. Declaring Variable Types • Use the Dim statement to declare the type of a variable. • Examples: Dim number As Integer Dim flower As String Dim interestRate As Single Chapter 3 - Visual Basic Schneider

  48. Data Types : • Single: a numeric variable that stores real numbers • Integer: a numeric variable that stores integer numbers (from -32768 to 32767) • String: a variable that stores a sequence of characters Chapter 3 - Visual Basic Schneider

  49. Using Text Boxes for Input/Output • The contents of a text box are always a string. • Numbers can be stored in text boxes as strings. Chapter 3 - Visual Basic Schneider

  50. Using Text Boxes for Input/Output • The contents of a text box should be converted to a number before being assigned to a numeric variable. • Val(txtBox.Text) gives the value of a numeric string as a number • Example: Dim numVar as Single numVar = Val(txtBox.Text) Chapter 3 - Visual Basic Schneider