Activity : Programming Methods
Below is an example of a section of program code (using Visual Basic) that calculates the total amount of an invoice with VAT added. 

Prices and Quantities are input repeatedly until a rogue value of 0 is input.

The first version is an example of bad programming...
Dim P As Single
Dim Q As Integer
Dim T, F As Single
Total = 0
Do
Price = InputBox("Please enter the Price")
If P <> 0 Then
Q = InputBox("Please enter the Quantity")
T = T + (P * Q)
End If
Loop Until (P = 0)
F = T + T * 17.5 / 100

 

 This is difficult to read, and difficult to make changes if needed.
The 'better' version is shown below...
'Declare Local variables
Dim Price As Single
Dim Quantity As Integer
Dim Total, FinalTotal, VATAmount As Single

'Declare Constant
Const VATRate = 17.5

'Initialise Total to 0
Total = 0

Do

    'Input Price
    Price = InputBox("Please enter the Price")

    'Check for rogue value
    If Price <> 0 Then
        Quantity = InputBox("Please enter the Quantity")
        Total = Total + (Price * Quantity)
    End If

Loop Until (Price = 0)

'Calculate VAT
VATAmount = Total * VATRate / 100

'Add VAT to total
FinalTotal = Total + VATAmount

 

 Longer code, so more typing...but much easier to understand!
How many improvements can you spot?

Click on the space below to see if you were right...
 

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