Writing General Procedures in VB6.0

VISUAL BASIC 6.0

WRITING GENERAL PROCEDURES

Procedures perform some specific task of the VB Project.

A procedure is a set of VB statement in a larger Project.

Advantages

  1. Decomposing complex problems into smaller subproblems
  2. Reducing duplication of code
  3. Reuse of code
  4. Improving readability of the VB Project

Creating a New Sub Procedure

Steps to add a new general procedure to a form:

  1. Display the Code window for the form
  2. Select Add Procedure from the Tools menu
  3. Enter a name in the Add Procedure dialog box
  4. Choose the Type of Procedure (Sub/ Function / Property / Event)
  5. Select Private or Public for Scope of the VB Project
  6. Clink OK

 


Types of Procedures

1.Sub Procedures – perform actions but do not return a value to the calling code

2.Function Procedures – perform actions and return a value to the calling code

3.Property Procedures – create and execute custom properties of an objects

4.Event Procedures - execute when a particular event occur on a particular object

 

1.Sub Procedures

  • A Sub Procedure is a set of VB statements enclosed by the Sub and End Sub statements.
  • The Sub procedure performs a task and then returns control to the calling code.
  • But it does not return a value to the calling code.

Syntax for declaring a Sub Procedure is

[scope]  Sub SubName[(Parameter List)]

Statement of the Sub Procedure

End Sub

The value of scope may be Public or Private

The Syntax for a call to a Sub Procedure is

[Call] SubName [(Parameter List)]

Passing Parameters: By Value or By Reference

VB supports two ways of passing parameters to procedures

  1. By Value (ByVal)
  2. By Reference (ByRef)

By Value (ByVal)

  • When pass arguments by values, the procedure works only with the copies of the values.
  • When work with large amount of data, this may lead to performance overheads.

By Reference (ByRef)

  • When pass arguments by reference, the procedure receives a reference to the actual values.
  • When modified, the original values are affected.
  • ByRef consumes more time and space efficient.
  • But it is more error prone.

Eamples

1. Dim A, B As String

Private Sub JOIN_Click()

Call add( )

End Sub

 

Public Sub add( )

A = "Welcome to "

B = "VB Programming World"

Label1.Caption = A & B

End Sub

 

2. Dim A, B As String

Private Sub JOIN_Click()

A = "Welcome to "

B = "VB Programming World"

call add(A, B)

End Sub

 

Public Sub add(ByVal X As String, ByVal Y As String)

Label1.Caption = X & Y

End Sub


2.Function Procedure

  • A Function Procedure is a set of VB statements enclosed by the Function and End Function statements.
  • The Sub procedure performs a task and then returns control to the calling code.
  • When it returns control, it returns a value to the calling code.

The Syntax for declaring a Function is

[scope]  Function FunctionName[(Parameter List)] As ReturnType

Statement of the Function Procedure

End Function

The syntax for a call to a Function is

[Call] FunctionName [(Parameter List)] (or)

Value = FunctionName [(Parameter List)]

Returning values

The Function returns a value to the calling code.

Example

Dim A, B As String

Private Sub JOIN_Click()

A = "Welcome to "

B = "VB Programming World"

Label1.Caption = add(A, B)

End Sub

 

Public Function add( X As String, Y As String) As String

Return X & Y

End Function

 

3.Property Procedure

  • A Property Procedure is a set of VB statements enclosed by the Property and End Property statements.
  • A Property procedure is used to create and manipulate custom properties.
  • It is used to create read only properties for Forms, Modules and Classes

Type of Property Procedures

Property Let Procedure – sets the value of a property

Property Get Procedure – returns the value of a property

Property Set Procedure – sets the reference to an object

 

4.Event Procedures

  • An event procedure is a set of statements that execute when a particular event occur on a particular object.
  • It contains the control’s actual name, an underscore and the event name.
  • The default scope of  Event Procedures is Private.

The Syntax for declaring Event Procedure is

[Scope] Sub ControlName_Event( )

Statement of the Sub Procedure

End Sub

Example

Private Sub Form_Load()

Caption = "Event Procedure"

End Sub

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