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Chapter 3

Chapter 3. Fundamentals of Programming in Visual Basic. Visual Basic Objects Visual Basic Events. Numbers Strings Input/Output Built-In Functions . Outline and Objective. The initial Visual Basic screen. Menu bar. Toolbar. Project Explorer window. Toolbox. Properties window.

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Chapter 3

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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 Objective Chapter 3 - Visual Basic Schneider

  3. The initial Visual Basic screen Menu bar Toolbar Project Explorer window Toolbox Properties window Form Chapter 3 - Visual Basic Schneider

  4. Steps to Create a Visual Basic Program 1. Create the Objects 2. Set Properties 3. Write the Code for each Event Chapter 3 - Visual Basic Schneider

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

  6. A Text Box Walkthrough: • Double-click on Text Box 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. A Text Box Walkthrough Text box Chapter 3 - Visual Basic Schneider

  8. Name Caption Border style Visible Back Color Alignment Font Some Useful Properties: Chapter 3 - Visual Basic Schneider

  9. Naming Objects: • Use the Propertywindow to change the Name property of an object • Good Programming habit is that each name begins with three letter prefix that identifies the type of control. Chapter 3 - Visual Basic Schneider

  10. Naming Objects: Chapter 3 - Visual Basic Schneider

  11. Visual Basic Events • Code is a set of statements that will be executed when you run a program. • Write Code for each Event. • Most Events are associated with Objects. • The code for each event is called an “Event Procedure”. Chapter 3 - Visual Basic Schneider

  12. The steps for creating a VB program: • Create the Interface. • Set Properties for the objects. • Write the code that executes when event occur. Chapter 3 - Visual Basic Schneider

  13. An Event Procedure Walkthrough • Create the interface. • Set Properties. • Double click on the object to open the Code window. • Click on the Procedure box to find the event • Write the code for that event. Chapter 3 - Visual Basic Schneider

  14. Example of An Event 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

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

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

  17. Variables • A storage location in main memory whose value can change 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

  18. Must begin with a letter. Can contain letters, numeric digits. Can have up to 255 characters. Can Not be restricted keyword. Rules for Creating Variable Names Chapter 3 - Visual Basic Schneider

  19. Used to store Numbers . The value is assigned either by the programmer or by calculation. Numeric Variables Chapter 3 - Visual Basic Schneider

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

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

  22. Constant • Similar to a variable, but 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: Integer Real 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. Numeric Constants in a Statement: tax = 0.02 * (income - 500 * dependence) sum = 2 + x + 4.6 + y Chapter 3 - Visual Basic Schneider

  26. String Constants: • A group of alphanumeric data consisting of any type of symbols. Chapter 3 - Visual Basic Schneider

  27. Valid String Constants “A rose by any other name” “Down By the Sea Shore” “134.23” “She said, ‘stop , thief!’” Chapter 3 - Visual Basic Schneider

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

  29. Arithmetic Operations & Hierarchy of 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

  30. Examples Evaluate the following expressions: x = 3 * 6 - 12 / 3 x = 4 ^ (8 / 4) y = 12 + 6 / (3 * (10 - 9)) z = 5 + 4 ^ 2 m = 6 / 3 + 3 Chapter 3 - Visual Basic Schneider

  31. Words that have predefined meaning to Visual Basic . Can Not be used as variable names. Example: Print Cls If While Keywords Chapter 3 - Visual Basic Schneider

  32. Print: Is a method used to display data on the screen or printer. Can be used to print value of variables. Can be used to print value of arithmetic expressions . Visual Basic Print Statement Chapter 3 - Visual Basic Schneider

  33. Example 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 2 * (3 + 4) End Sub Chapter 3 - Visual Basic Schneider

  34. picOutput.Print speed picOutput.Print taxRate picOutput.Print “Class average is”; total / 3 Example of Print Statement Chapter 3 - Visual Basic Schneider

  35. x = 15 y = 5 picOutput.Print (x + y) / 2, x / y Example Chapter 3 - Visual Basic Schneider

  36. 10 3 Output Chapter 3 - Visual Basic Schneider

  37. Internal Documentation • An apostrophe (‘) can be used to indicate comments; comments are ignored by Visual Basic. • The keyword Rem can also be used instead of an apostrophe for comments. • Remarks can also be placed after program statement too. Chapter 3 - Visual Basic Schneider

  38. Visual Basic Assignment Statement • The statement var = expr assigns the value of the expression to the variable. • Assigns the value of the expression on the right to the variable on the left. Chapter 3 - Visual Basic Schneider

  39. Example Private Sub cmdCompute_Click( ) picResults.Cls a = 5 b = 4 c = a * (2 + b) picResults.Print c End Sub Chapter 3 - Visual Basic Schneider

  40. Valid Assignment Statement count = count + 1 num = 5 count = count + num /2 Chapter 3 - Visual Basic Schneider

  41. 10 = count count + 1 = count Invalid Assignments Chapter 3 - Visual Basic Schneider

  42. A String variable stores character strings. The rules for naming string variables are identical to those of numeric variables. When a String variable is first declared, its value is the null string. (that is, the empty string). String Variables Chapter 3 - Visual Basic Schneider

  43. 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 Example of String Variable Chapter 3 - Visual Basic Schneider

  44. Two string can be combined with the concatenation operation. Concatenation is represented with the ampersand ( & ) sign. Concatenation Chapter 3 - Visual Basic Schneider

  45. strVar1 = “Hello” strVar2 = “World” picOutput.Print strVar1& strVar2 Example of Concatenation: Chapter 3 - Visual Basic Schneider

  46. txtBox.Text = “32” & CHR(176) & “ Fahrenheit” Example of Concatenation Chapter 3 - Visual Basic Schneider

  47. Data Types • Each variable in the program is assigned to a data type. Chapter 3 - Visual Basic Schneider

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

  49. Data Types : • Single-precision numeric variable: Stores real numbers • Double-precision numeric variable: Stores real numbers with many digits • Integer: Stores integers • Long integer: Stores integers with many digits Chapter 3 - Visual Basic Schneider

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

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