Sub Procedures and Functions

1
Sub Procedures and Functions

• Advanced GISWeek 2/3
• 2008 Spring

2
Subroutines (or subprocedures in VB) Dont
return value

• Option Explicit manually check variable
  declaration
• Dim intMyNumber As Integer Dim outside Sub
• Private Sub cmdCalcualte_Click()
• intMyNumber InputBox("Input your number")
• Call SquareNumber
• End Sub
• Private Sub SquareNumber()
• lblAnswer.Caption intMyNumber intMyNumber
• End Sub

3
Passing arguments to subroutines

• Private Sub SquareNumber(intNum As Double)
• lblAnswer.Caption intNum intNum
• End Sub
• Private Sub cmdCalculate_Click()
• intMyNumber InputBox (Input your _
  number)
• Call SquareNumber(intMyNumber)
• End Sub

4
Exercise create a sub procedure with two
arguments for calculating area of a rectangle

• Private Sub Area(x as single, y as single)
• lblAnswer.Caption x y
• End Sub
• Private Sub cmdCalculate_Click() need to
  declare _ width/height
• width Inputbox (Input width of a square)
• height inputbox (Input height of a square)
• Call Area(width, height)
• End Sub

5
Exercise finding minimum values

• Private Sub cmdSmallest_Click()
• Dim value1 as Long, value2 as Long, value3 as
  Long
• value1 txtOne.Text
• value2 txtTwo.Text
• value3 txtThree.Text
• Call Minimum(value1, value2, value3)
• Private Sub Minimum (min as Long, y as Long, z as
  Long)
• If y lt min Then
• min y
• End if
• If z lt min Then
• min z
• End If
• lblSmallest.Caption Smallest value is
  min
• End Sub

6
ByVal or ByRef

• Parameters can be passed byVal or byRef
• byRef passes the memory location of the
  argument to the subprogram instead of the
  arguments value.
• Allows subprogram to change
• Deafult
• byValue pass the copy of variable. If value of
  copy changed, the original will not.

7
What will happen if cmdClick clicked 10 times?
What if ByVal is replaced with ByRef?

• Private Sub cmdClick()
• Dim Number1 As Integer
• Number1 10Call IncrementVariable(Number1)
• MsgBox(Number1)
• End Sub
• --------------------------------------------------
  -----------------------
• Private Sub IncrementVariable(ByVal Number1 As
  Integer)Number1 Number1 1
• End Sub

8
Functions return values which determines data
type of functions

• Return a value from a function by assigning it to
  the name of the function itself. Basically, the
  function is treated as though it were a variable.
• In slides 10, the SqureNumber sub can only change
  the lblAnswer.Caption. If a function is in place
  such as the follows
• Option Explicit
• Dim intMyNumber As Integer
• Private Function SquareNumber(intNum As Double)
  As Double
• SquareNumber intNum intNum
• End Function
• Private Sub cmdCalcualte_Click()
• Dim intMyNumber As Double
• intMyNumber txtNum.Text
• lblAnswer.Caption SquareNumber(intMyNumber)
• End Sub

9
Built-in Functions

• String, numeric, date and time, financial
  functions.
• Commonly used String functions
• LCase/UCase converts to L/U case
• Len return length of string
• Left/Right/Mid return specified number of cha.
  form left/right/middle side of a string.
• Replace replace one or more occurrence of a
  string inside another
• LTrim/RTrim/Trim removes spaces from the
  beginning (end)(both ends) of a string.
• InStr/InStrRev returns the position of the
  first(last) occurrence of one string within
  another
• Join return a string created by joining a number
  of substrings contained in an array.

10
Numeric/Date/Time

• Commonly used functions
• Abs/Sin/Cos/Tan/Atn(arctangent)/Exp/Log/
  Sqr/Sgn(sign of a number)/Rnd (random
  number)/Int,Fix (integer portion of a number)
• Date-current system date
• DateAdd- add specified interval to a date
• DateDiff - differ of two specified dates

11
Public or Private

• Public subprocedures are declared like this
• Public Sub ltsubprocedure namegt
• Public Function ltfunction namegt As ltreturn typegt
• A public routine can be accessed throughout the
  program but a private can only called in the same
  Form or Module
• Advantage of using Private
• use less memory, code protected within one
  corner, and names used over and over

12
Variable Scope
13
Static statement - to preserve the values of
procedure-level variables, use Static
VariableName As data type

• used to maintain the values of variables between
  calls of the procedure.
• Try this
• Private Sub Command1_Click()
• Static intNum As Integer
• intNum intNum 1
• MsgBox intNum
• End Sub
• Try to run these code several times, the
  increment of
• intNum can be shown in Static but not Dim