Sub Procedures

A sub procedure is commonly used to accept input, display information, print information, manipulate object properties, or perform other specific tasks. Unlike an event procedure, it is not automatically tied to a runtime event such as clicking a button. Instead, it is called explicitly from other code whenever the task needs to be performed.

This makes sub procedures very useful for:

• Reducing repeated code
• Keeping the main program shorter and clearer
• Organizing logic into smaller reusable parts
• Improving readability and maintenance

A sub procedure begins with the Sub keyword and ends with the End Sub keyword. The general structure is:

Sub ProcedureName(parameter)
    Statements
End Sub

The parameter is optional. If a procedure needs external data in order to do its job, that data can be passed into the procedure through parameters.

A parameter is data supplied to the procedure from outside. Parameters let one sub procedure work with different values each time it is called.

For example, a procedure that adds two numbers can be reused with many different pairs of values instead of hard-coding the numbers inside the procedure.

In this example, a sub procedure named sum accepts two parameters and displays their total in a message box.

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    sum(5, 6)
End Sub 

Sub sum(a As Single, b As Single)
    MsgBox("sum=" & a + b)
End Sub

When the form loads, the main procedure calls sum(5, 6). The numbers 5 and 6 are passed into the sub procedure as the parameters a and b. The sub procedure then calculates the result and shows it in a message box.

This example demonstrates how a program can repeatedly generate possible passwords and compare them with the actual password. It uses a timer together with a sub procedure named generate().

The key idea is that the timer repeatedly calls the procedure. This makes it possible to perform the same task over and over without rewriting the logic each time.

In the original lesson, the timer interval is set to 100, which means 0.1 seconds. The timer is disabled at first and only starts after the user clicks the button.

The functions used include:

• Rnd() generates a random number between 0 and 1.
• Int(...) removes the decimal part and returns an integer.
• Timer1_Tick runs at the chosen interval while the timer is enabled.

Public Class Form1
    Dim password As Integer
    Dim crackpass As Integer

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Timer1.Enabled = True
    End Sub

    Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick

        generate()

        If crackpass = password Then
            Timer1.Enabled = False
            Label1.Text = crackpass
            MsgBox("Password Cracked! Login Successful!")
        Else
            Label1.Text = crackpass
            Label2.Text = "Please wait..."
        End If

    End Sub

    Sub generate()
        crackpass = Int(Rnd() * 100) + 100
    End Sub

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        password = 123
    End Sub
End Class

Here is how the program works:

• The real password is stored in the variable password.
• When the user clicks the button, the timer starts.
• Each timer tick calls the generate() procedure.
• The procedure creates a random three-digit number between 100 and 199.
• The generated value is compared with the actual password.
• If both match, the timer stops and the program displays a success message.

This example is a useful demonstration of how sub procedures can be called repeatedly to perform a specific task.

At first, the generated password values keep changing while the program searches. When the generated value matches the correct password, the timer stops and login is shown as successful.