Question

In Visual Basic:

Think of a function, then write its definition and document what the function does. Examples that are appropriate: Check if a number is negative, if a number is even, if a number is odd. Other examples include, a function that returns the the smallest number in an array, the largest number in an array, the average of an array.

Your answer must be unique and not from the book, so make sure you read all posted messages before you post your example.

Answer 1

This is a full program for prime number checking, it uses function.
We should have a form named form1, and one label, one textbox and a button.
We must change some properties of these controls.

Control	property	changes
Label1	text	change the text property to " enter an integer"
TextBox1	name	chage name totxtPrime
Button1	txt,name	change name to btnPbtnPrimeOrNot and text to Check Prime

After change these properties, double click the button, we would redirected to the code window. Write the following code there.

Public Class Form1

Private Function PrimeN(num As Integer)As Integer
Dim i as Integer

'This is the called PrimeN Function, note that it has one argument num with Integer data type. The 'As Integer' statement outside the parenthesis indicates the function returns an integer value.

PrimeN=1

'Set PrimeN variable to 1 at first. Then divide each of the variables from 2 to n-1, and take its reminder. If the reminder is 0, which means it is also a factor of num. A prime number has only two factors 1 and the number it self.

For i = 2 To (num – 1)

If num Mod i = 0 Then

PrimeN = 0

'Set PrimeN to 0, if any numbers in the loop give a reminder 0, which means it is not a prime. Then we dont want to check other i values. So exit from loop

Exit For

'Exiting from loop

End If

'End of if statement

Next

'end of loop

End Function

'end of function

Private Sub btnPrimeOrNot_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPrimeOrNot.Click

'When double click the button we would be here

Dim num, status As Integer

'declaring num for storing textbox value

num = Val(txtPrime.Text)

'Val() method convert the textbox string data into integer and assign it to num.

status = PrimeN(num)

'calling Function named PrimeN(), and assign the returned value to status variable.

If status = 0 Then

'After returned from called Function status variable should contain either 0 or1. If it is 0, then show message not prime

MessageBox.Show(“Not prime”)

Else

'If status is 1, show message as Prime

MessageBox.Show(“prime”)

End If

'end if stetement

End Sub

'end sub routine

End Class