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Visual Basic : Core 1

Visual Basic : Core 1. Projects Data types Variables and constants Comments, hex constants and line continuation Forms and controls A calculator program. What's in a Project. Project = code for an application Form = window – several in a project

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Visual Basic : Core 1

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  1. Visual Basic : Core 1 • Projects • Data types • Variables and constants • Comments, hex constants and line continuation • Forms and controls • A calculator program

  2. What's in a Project • Project = code for an application • Form = window – several in a project • .frm has data eg form width height, and event-driven subroutines • Module = VB code (general) • Class = defining your own classes • Can make into .exe

  3. Project files

  4. VERSION 5.00 Begin VB.Form Form1 Caption = "Form1" ClientHeight = 2445 ClientLeft = 5145 ClientTop = 4110 ClientWidth = 5070 LinkTopic = "Form1" ScaleHeight = 2445 ScaleWidth = 5070 Begin VB.CommandButton Command1 Caption = "Command1" Height = 615 Left = 1200 TabIndex = 0 Top = 600 Width = 1815 End End Attribute VB_Name = "Form1" Attribute VB_GlobalNameSpace = False Attribute VB_Creatable = False Attribute VB_PredeclaredId = True Attribute VB_Exposed = False Option Explicit Private Sub Command1_Click() MsgBox ("Hello world") End Sub Inside a .frm file

  5. Variables • Dim x as Integer • Dim x,y as Integer NO! • Is case sensitive (kind of) • Variable naming conventions • Microsoft Simonyi Hungarian Reddick • House rules • Assignment statement – x = 4 • Option Explicit YES! • Constants – Private Const MyInt As Integer = 5

  6. Comments, line continuation and hex • Comments start with an apostrophe • 'and run to the end of the line • A very long statement can use a_ to continue onto the next line • Hex constants written like &HFF0012

  7. Data types • Integer Long • Single Double • Currency • Byte unsigned 0 - 255 • String • Boolean • Date • Object • Variant - do not use except explicit reason

  8. VarType to determine type 0 Empty (uninitialized) 1 Null (no valid data) 2 Integer 3 Long integer 4 Single-precision floating-point number 5 Double-precision floating-point number 6 Currency value 7 Date value 8 String 9 Object 10 Error value 11 Boolean value 12 Variant (used only with arrays of variants) 13 A data access object 14 Decimal value 17 Byte value 36 Variants that contain user-defined types 8192 Array Dim x As Variant x = 1 MsgBox (VarType(x))

  9. Data type conversion DIM x as integer x = Cint("10")

  10. Form properties

  11. Controls and properties

  12. Example - calculator Private Sub Command1_Click() Dim num1 As Integer Dim num2 As Integer Dim result As Integer num1 = Text1.Text num2 = Text2.Text result = num1 + num2 Label1.Caption = result End Sub Exercise – try this out. Then add and program subtract, multiply and divide buttons. Ignore invalid numbers and divide by zero – done later

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