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This review covers the basics of Visual Basic programming, including object definitions, event handling, and the use of forms and controls. Learn about properties, methods, variables, arrays, and more.
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Visual Basic Review LBS 126
VB programming Project Form 1 Form 2 Form 3 Button Text box Button Text box Picture box Objects 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. VB object Properties (size, Caption…) Methods (Print…) Event Handler (Command1_Click())
Handling the event Get Text1.text Properties Text box Methods Message Dispatching Block Event Handler User Properties Button Methods Event Handler Command1_Click Print Properties Picture Box You have got clicked. Methods Event Handler
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(argumentslist)
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-elseblocks • 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