MIC 305 Session 3

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MIC 305Session 3

• General Procedures

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Outline Objective

• Creating Visual Basic Sub Procedures
• Creating User-defined Function Procedures
• Parameter Passing Mechanism
• Modularizing in Programming Languages

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What is Modularization

• Breaking the program into subtasks
• A Sub procedure or Function performs a
  well-defined task
• Easier to test, debug and correct

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Why use Sub procedures and Functions?

• Provide abstract operations
• Make programs easier to write, debug and maintain.

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Modularizing Programs in Visual Basic

• In Visual Basic, there are two types of
  procedures
• Sub
• Function

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Passing Arguments to Subs

• When you define a Sub procedure sometimes you
  need to transfer variables that are used in
  different Subs. This is called passing in
  programming languages.

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Sub Procedures Properties

• may be called
• may be passed data called arguments
• may return values to the calling program
• may change the data stored in a received
  variable

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Components of Sub Procedure

• name used to identify the Sub procedure
• parameters a Sub procedure accepts values from
  the caller through its parameters it may also
  send values back to the caller through its
  parameters.

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Sub Procedure's Name

• The rules for naming Sub Procedures are the same
  as naming variables.
• In this text, Sub procedure names begin with
  uppercase letters in order to distinguish them
  from variable names.

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Syntax of a Sub Procedure

• Private Sub ProcedureName ( )
• statement(s)
• End Sub

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Creating Visual Basic Sub Procedure

• Activate a code window
• Select Add Procedure from the Tools menu
• Type in the name of the Sub procedure
• Click on Private in Scope frame
• Press the Enter key or click the OK button
• Type the statements of the Sub procedure into
  this window

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Example of Call to a Sub Procedure

• Private Sub cmdCompute_Click()
• Dim num As Single
• num Val(InputBox("Enter a number"))
• Call Triple(num)
• End Sub

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Sub Procedure Triple

• Private Sub Triple(num As Single)
• ' Multiply the value of the number by 3
• picResult.Print "The number is" 3 num
• End Sub

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Passing Arguments to Sub Procedures

• Arguments Variables or expressions placed in
  parentheses in a Call statement.
• Not only is the value of the argument passed to
  the parameter, but the value of the parameter is
  passed back to the argument.

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Example of Arguments

• Call Triple(num)

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Parameters

• Variables placed in parentheses after a Sub
  Procedure's name.
• When the procedure is called, the values of the
  corresponding arguments are placed in the
  parameters.

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Example of Parameters

• Private Sub Triple(num As Single)

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Passing arguments to parameters

• Call Triple(num )
• Private Sub Triple (num As Single)

Argument
Parameter
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Passing Arguments to Parameters

• Call Add (x, y )
• Private Sub Add ( num1 As Single, num2 As Single)

Arguments
Parameters
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Important Rules for Passing Arguments to a Sub

• The number of arguments and parameters must
  match.
• The data type of each argument must match its
  corresponding parameter.

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Local Variables

• A variable that is used only in a specific
  procedure (Sub or Function).
• The scope of the local variable is the portion of
  a Sub or Function in which that variable has
  been defined.

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Local Variables

• Declared within a procedure definition
• Private to a procedure definition
• Variables in different procedures are totally
  independent
• different procedures can have variables with the
  same names however, each variable will have its
  own memory location

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Advantages of Local Variables

• Extremely useful for team programming
• To protect side effect (which is an accidental
  change of the value of the variable)

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Example of Local Variables

• Private Sub cmdButton_Click()
• Dim var1 As Integer, var2 As Integer,num As
  Integer
• var1 2
• var2 4
• Call Add(num)
• picBox.Print num
• End Sub

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Sub Add

• Private Sub Add(num As Integer)
• Dim var1 As Integer, var2 As Integer
• num var1 var2
• End Sub

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Form-Level Variables

• Form-level variables are visible to every
  procedure (Global variable).
• Form-level variables appear at the top of the
  code window.

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How to create Form-Level Variables?

• Activate the code window
• Click on the down arrow to the right of the
  object list box
• Click on General
• Click on Declaration in the procedure list box
• Type in Dim statements for form-level variables

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Example

• ' In Declaration section of General
• Dim num1 As Single, num2 As Single

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Review

• Visual Basic has two types of procedures
• Sub
• Function
• Each Sub procedure performs a distinct task.
• The Call statement causes a Sub procedure to be
  executed.

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Review

• Values can be passed between the calling program
  and Sub by passing arguments.
• The number and type of arguments in the calling
  program and Sub must match.

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Review

• Structure charts are useful in determining how to
  divide a program into Sub procedures.
• Modularizing programs offers significant
  advantages.
• Easier to maintain
• Extremely useful for team programming
• Side effect can be prevented