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 2017, 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 function in next lesson.
A sub procedure is usually used to accept input from the user, display information, print information, manipulate properties or perform some other tasks. It is a program code by itself and it is not an event procedure because it is not associated with a runtime procedure. It is called by other code whenever it is required to perform a certain task.
Sub procedures help to make programs smaller and seamless to manage. A sub procedure begins with a Sub keyword and ends with an End Sub keyword.
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.
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
This is Visual Basic 2017 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 the actual password or not. If they are equal, the passwords generating process will be terminated by setting the Timer1.Enabled property to false.
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