Visual Basic Review

1. Visual Basic Review LBS 126

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

3. 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

4. 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())

5. 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

6. 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

7. 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

8. 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

9. 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.

10. 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”

11. 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.

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

13. 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.

14. 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)

15. 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

16. 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.

17. 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.

18. 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

19. 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

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

21. 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

22. 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

23. 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

24. 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