Procedures in Visual Basic 6

Visual Basic offers different types of procedures to execute small sections of coding in applications. The various procedures are elucidated in details in this section.Visual Basic Program can be broken into smaller logical components called Procedures. Procedures are useful for condensing repeated operations such as the frequently used calculations, text and control manipulation etc. The benefits of using procedures in programming are:

It is easier to debug a program a program with procedures, which breaks a program into discrete logical limits.

Procedures used in one program can act as building blocks for other programs with slight modifications.

A Procedure can be Sub, Function or Property Procedure.

Sub Procedures

A sub procedure can be placed in standard, class and form modules. Each time the procedure is called, the statements between Sub and End Sub are executed. The syntax for a sub procedure is as follows:

[Private | Public] [Static] Sub Procedurename [( arglist)]
[ statements]
End Sub

arglist is a list of argument names separated by commas. Each argument acts like a variable in the procedure. There are two types of Sub Procedures namely general procedures and event procedures.

Event Procedures

An event procedure is a procedure block that contains the control's actual name, an underscore(_), and the event name. The following syntax represents the event procedure for a Form_Load event.

Private Sub Form_Load()
....statement block..
End Sub

Event Procedures acquire the declarations as Private by default.

General Procedures

A general procedure is declared when several event procedures perform the same actions. It is a good programming practice to write common statements in a separate procedure (general procedure) and then call them in the event procedure.

In order to add General procedure:

·         The Code window is opened for the module to which the procedure is to be added.

·         The Add Procedure option is chosen from the Tools menu, which opens an Add Procedure dialog box as shown in the figure given below.

·         The name of the procedure is typed in the Name textbox

·         Under Type, Sub is selected to create a Sub procedure, Function to create a Function procedure or Property to create a Property procedure.

·         Under Scope, Public is selected to create a procedure that can be invoked outside the module, or Private to create a procedure that can be invoked only from within the module.

We can also create a new procedure in the current module by typing Sub ProcedureName, Function ProcedureName, or Property ProcedureName in the Code window. A Function procedure returns a value and a Sub Procedure does not return a value.

Function Procedures

Functions are like sub procedures, except they return a value to the calling procedure. They are especially useful for taking one or more pieces of data, called arguments and performing some tasks with them. Then the functions returns a value that indicates the results of the tasks complete within the function.

The following function procedure calculates the third side or hypotenuse of a right triangle, where A and B are the other two sides. It takes two arguments A and B (of data type Double) and finally returns the results.

Function Hypotenuse (A As Double, B As Double) As Double
Hypotenuse = sqr (A^2 + B^2)
End Function

The above function procedure is written in the general declarations section of the Code window. A function can also be written by selecting the Add Procedure dialog box from the Tools menu and by choosing the required scope and type.

Property Procedures

A property procedure is used to create and manipulate custom properties. It is used to create read only properties for Forms, Standard modules and Class modules.Visual Basic provides three kind of property procedures-Property Let procedure that sets the value of a property, Property Get procedure that returns the value of a property, and Property Set procedure that sets the references to an object.