Lesson 16 Creating Sub Procedure

A procedure is a program code that can carry out certain tasks or return a value. It can be called from other procedures. In Visual Basic 2019, there are two types of procedures;  sub procedures and functions. A sub procedure(also call subroutine) is a procedure that performs a specific task and does not return a value while a function is a procedure that returns a value. We will learn about the function in the next lesson.

The structure of a sub procedure is as follows:

Sub ProcedureName (parameter)
Statements
End Sub

The parameter is a certain data that is passed into the sub procedure to perform a specified task.

Example 16.1

In this example, we create a sub procedure, to sum up two values that are specified by the parameters. The main program can reference a procedure by using its name together with the parameters in the parentheses.

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 

Running the program produces a message box as shown in Figure 16.1

Example 16.2: Password Cracker

This is a Visual Basic 2019 program that demonstrates how to crack passwords. It can generate possible passwords and compare each of them with the actual password; and if the generated password found to be equal to the actual password, login will be successful.

In this program, a timer is inserted into the form.We create passwords generating procedure generate () and it is called by the Timer1_Tick() event so that the procedure is repeated after every interval. The interval of the timer can be set in its properties window. A value of 1 is 1 millisecond and a value of 1000 is 1 second. We shall set the Timer's interval at 100 which is equivalent to 0.1 seconds. The Timer1.Enabled property is set to false so that the program will only start generating the passwords after the user clicks on the Generate button. Rnd is a function that generates a random number between 0 and 1. Multiplying Rnd by 100 will produce a number between 0 and 100. Int is a function that returns an integer by ignoring the decimal part of that number.

Therefore, Int(Rnd*100) will produce a number between 0 and 99, and the value of Int(Rnd*100)+100 will produce a number between 100 and 199.Finally, the program uses If…Then…Else to check whether the generated password is equal to the actual password or not. If they are equal, the passwords generating process will be terminated by setting the Timer1.Enabled property to false.

The Code

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 

The output