Visual Basic Review LBS 126

VB programming Project Form 1Form 2Form 3 Text boxButton Picture box Objects Text box Button Objects

Definitions Form contains the Main Program Controls are user interface elements (text boxes, commands) in the Form Forms and Controls are referred to as OBJECTS

Objects in VB Everything in VB is objects, forms, buttons, … Three elements of objects. Properties Methods Event handlers. Important properties of common objects. Properties (size, Caption…) Methods (Print…) Event Handler (Command1_Click()) VB object

Handling the event Message Dispatching Block User Text box Properties Methods Event Handler Button Properties Methods Event Handler Command1_Click Picture Box Properties Methods Event Handler Print Get Text1.text You have got clicked.

Define event handler When you double click the command button, you only define the default event handler (command1_click). Other event can be defined as well. Then procedure name of the event handler. Private Sub ObjectName_EventName() End Sub

Variables Different Types: Byte, Integer, Long, Single, String Naming Starting with letter No special symbols, like ^ $ % Less than 255 characters. Key words are reserved. Declare Variable Dim VariableName As Variable Type

Declaring Arrays Use Dim key word to declare arrays, just as what we do for variables. Dim Data(1 to 50) As Single Dim Species(1 to 4) As String Accessing values in an array with subscript. Data(44) = 22.5; Species(1) = “ACTGACTCGTAACGT” Red Number is INDEX Use ReDim when declaring an array size based on a variable User tells you there are 50 values (count = 50) ReDim Values(1 to count) as Single

Scope of a variable Local scope. Variable declared in a sub procedure It only exists in this sub procedure. Form-level scope. Variable declared out of any sub procedure. Any sub procedure can read it.

Two meanings of “ = “ sign Assignment operator: assign the value of the RIGHT side to the LEFT side. Dim A as Integer A=0 A=A+1 Relational operator If A = B Then Reads “A is assigned with A+1” Reads “If A equals to B then”

Strings String data is defined between two double quotations. “Hello world” String variable is a name used to refer to a string. String1=“Hello world” String is just a bunch of ASCII codes. You can not do mathematical operations on string.

String operations and functions Concatenation String relations =, <>,, = String functins Len(), Val(), Str(), Ucase()… Read text pp. 51

Sub procedures and Functions Procedures and functions are pre-defined code fragments. Why using procedures and functions Making code better structured. Reusing code. Three types of procedures. Event procedure (event handler) General procedure Function procedure Different between Sub procedure and Functions.

General Procedures Defined by key word Sub Private Sub ProcedureName() Block of code End Sub Not linked with any event Can be called by other part of code. Call ProcedureName(arguments list)

Functions procedure Function is a sub procedure with a returned value. Function procedure is used in the same way as a built-in numeric or string function. Variable = FunctionName(arguments…) Define a function Private Function FunctionName(arg1 As type1, arg2 As type2,…) As ReturnType Block of code FunctionName=expression End Function

Passing arguments to and from procedure Passing by reference Sum(num1, num2) Create a tunnel that a procedure can output the computing results. Passing by value Sum((num1),num2) Isolate the procedure from it external world.

Comparison Operators See table 5.1 = equal to <> unequal to < less than > greater than <= less than or equal to >= greater than or equal to Works both for numbers and strings.

Logical Operators And, Or, Not a >=b And b <> 2 a >=b Or b <> 2 And statements: Both must be true Or statements: one or both must be true Not statements: True if statement is false

Boolean value Comparison operator and logical operator will return a Boolean value. Dim VariableName as Boolean Boolean value has only two possibilities: True and False Boolean value can be directly used in decision structure, do while loop, etc. If boolean_variable Then… Do While boolean_variable

Decision structure Simple If statement IF Boolean_Condition Then End IF If-then-else blocks Nested decision blocks. If –ElseIf- Elseif… – Else blocks

Select Case Blocks Allows multiple options (not just true or false) Select Case Variable Case Condition1 Case Condition2 Case Condition3 Case Else End Select Read text pp. 114

Repetition struction Do while Loop When times of loop is unknow Do while condition Loop For Next loop Fixed number of loops For variable = start# to end# Next varialbe

Three steps of reading data from file Step 1:Open the plain text file Open “filename.txt” For Input As #1 Step 2: Read data Input #1, variable Step 3: Close file Close #1

VB and Excel How to exchange data between VB and Excel..csv file How to write a user defined function in Excel. Private Function FuncName(arg1 as type1) as type End Function