Visual Basic Core 1 Projects Data types Variables

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 • . frm has data eg form width height, and event-driven subroutines • Module = VB code (general) • Class = defining your own classes • Can make into. exe

Project files

VERSION 5. 00 Begin VB. Form 1 Caption = "Form 1" Client. Height = 2445 Client. Left = 5145 Client. Top = 4110 Client. Width = 5070 Link. Topic = "Form 1" Scale. Height = 2445 Scale. Width = 5070 Begin VB. Command. Button Command 1 Caption = "Command 1" Height = 615 Left = 1200 Tab. Index = 0 Top = 600 Width = 1815 End Attribute VB_Name = "Form 1" Attribute VB_Global. Name. Space = False Attribute VB_Creatable = False Attribute VB_Predeclared. Id = True Attribute VB_Exposed = False Option Explicit Private Sub Command 1_Click() Msg. Box ("Hello world") End Sub Inside a. frm file

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 My. Int As Integer = 5

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 &HFF 0012

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

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

Data type conversion DIM x as integer x = Cint("10") Conversion function Converts an expression to Cbool Boolean Cbyte Byte Ccur Currency Cdate Date CDbl Double Cint Integer CLng Long CSng Single CStr String Cvar Variant CVErr Error

Form properties

Controls and properties

Example - calculator Exercise – try this out. Then add and program subtract, multiply and divide buttons. Ignore invalid numbers and divide by zero – done later Private Sub Command 1_Click() Dim num 1 As Integer Dim num 2 As Integer Dim result As Integer num 1 = Text 1. Text num 2 = Text 2. Text result = num 1 + num 2 Label 1. Caption = result End Sub