This is a Visual Basic program that generates a geometric progression and displays the results in a list box. Geometric progression is a sequence of numbers where each subsequent number is found by multiplying the previous number by a fixed number. The fixed number is called the common ratio. The common ratio can be negative, an integer, a fraction and any number but it must not be a zero.

The formula to find the nth term of the geometric progression is
ar^{n-1} , where a is the first number and r is the common ratio.

In visual basic, we employs the **Do.... Loop Until **statement to generate the numbers in a geometric progression.In this program, we need to insert three text boxes for the user to enter the first number, the common ratio and the number of terms. We also need to insert a list box to list the numbers. Besides that, a command button is need for the user to generate the numbers in the geometric progression.

To add the numbers to the list box, we use the **AddItem** method. The syntax is **List1.AddItem** n, where n can be any variable. The runtime interface is
shown in the figure below.

Private Sub cmd_compute_Click()

Dim x, n, num As Integer

Dim r As Single

x = Txt_FirstNum.Text

r = Txt_CR

num = Txt_Terms.Text

List1.AddItem "n" & vbTab & "x"

List1.AddItem "___________"

n = 1

Do

x = x * r

List1.AddItem n & vbTab & x

n = n + 1

Loop Until n = num + 1

End Sub

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