Specification

Design a program which asks the user to input the radius of a circle. The program should then calculate and display the circumference and area of the circle, both rounded to 2 decimal places.

Designing the code

From "asks the user to input the radius of a circle" we can see that:

• The user needs to input radius
• The program will need to remember the radius

From "It should then calculate and display the circumference and area of the circle" we can see that:

• The program has to calculate the circumference
• The program has to calculate the area
• The program will need to display the circumference
• The program will need to display the area

From "rounded to 2 decimal places" we can see that:

• The program has to round the circumference to 2 d.p.
• The program has to round the area to 2 d.p.

Put these steps into a suitable order and add detail if necessary:

1. Get radius from user
2. Calculate circumference (π * radius * 2)
3. Round circumference to 2 d.p.
4. Calculate area (π * radius ^ 2)
5. Round area to 2 d.p.
6. Display circumference
7. Display area

Designing the user interface

VB code - solution

VB code - alternative solution

This solution assumes the form contains a textbox (called txtRadius) and two labels (called lblOutputCircumf and lblOutputArea): Dim radius As Integer Dim circumf As Single Dim area As Single radius = txtRadius.Text circumf = Math.PI * radius * 2 circumf = Math.Round(circumf,2) area = Math.PI * radius ^ 2 area = Math.Round(area,2) lblOutputCircumf.Text = “The circle’s circumference is “ & circumf lblOutputArea.Text = “The circle’s area is “ & area

This solution would require a different user interface design as it uses InputBoxes and MessageBoxes: Dim radius As Integer Dim circumf As Single Dim area As Single radius = InputBox ("Please enter the radius") circumf = Math.PI * radius * 2 circumf = Math.Round(circumf,2) area = Math.PI * radius ^ 2 area = Math.Round(area,2) MsgBox (“The circle’s circumference is “ & circumf) MsgBox (“The circle’s area is “ & area)

Specification

Create a prototype program which gives information about tax rebates.

Your program will ask for the names and incomes of 6 people.
If a person’s income is less than £18000 then they will be due a tax rebate.

The user should input the name and income of six people. Income should be validated to ensure it is greater than 0.
The program will store all names and incomes and whether or not they qualify for a rebate.
The program should output:

• all of the names and incomes
• the total number of people who qualify for the rebate.

Designing the code

1. DECLARE names AS ARRAY OF STRING INITIALLY []
2. DECLARE income AS ARRAY OF INTEGER INITIALLY []
3. DECLARE rebate AS ARRAY OF BOOLEAN INITIALLY []
4. DECLARE rebate_count AS INTEGER INITIALLY 0


5. FOR person FROM 0 TO 5 DO


6.         RECEIVE names [person] FROM KEYBOARD
7.         RECEIVE income [person] FROM KEYBOARD


8.         WHILE income [person] <=0 DO
9.                 SEND “Please enter an income larger than 0” TO DISPLAY
10.                 RECEIVE income [person] FROM KEYBOARD
11.         END WHILE


12.         IF income [person] < 18000 THEN
13.                 SET rebate [person] TO TRUE
14.                 SET rebate_count TO rebate_count + 1
15.         ELSE
16.                 SET rebate [person] TO FALSE
17.         END IF


18. END FOR


19. FOR person FROM 0 TO 5 DO
20.         SEND names [person] TO DISPLAY
21.         SEND income [person] TO DISPLAY
22. END FOR


23. SEND rebate_count & “ people qualified for the rebate.” TO DISPLAY

Designing the user interface

This is where a lovely wireframe will go. But I haven't scanned it in yet.

VB code - solution

This solution assumes the form contains a listbox (called lstOutput):

Dim names (5) As String
Dim income (5) As Integer
Dim rebate (5) As Boolean
Dim rebate_count As Integer

For person = 0 To 5
        name (person) = InputBox("Please enter your name")
        income (person) = InputBox("Please enter your income")

        Do While income (person) <=0
                income (person) = InputBox (“Please enter an income larger than 0”)
        Loop

        If income (person) < 18000 Then
                rebate (person) = True
                rebate_count = rebate_count + 1
        Else
                rebate (person) = False
        End If
Next

For person = 0 To 5
        LstOutput.Items.Add name (person)
        LstOutput.Items.Add income (person)
Next

LstOutput.Items.Add rebate_count & “ people qualified for the rebate.”


Testing

Testing the input validation of income

Type of data	Income	Expected result	Actual result
Normal	15000	Input accepted and program continues	As expected
Normal	7500	Input accepted and program continues	As expected
Extreme	1	Input accepted and program continues	As expected
Exceptional	0	Prompted to re-enter income - "Please enter an income larger than 0"	As expected
Exceptional	-40000	Prompted to re-enter income - "Please enter an income larger than 0"	As expected
Exceptional	Omelette	Prompted to re-enter income - "Please enter an income larger than 0"	Program crashed as it expected an integer. I may try to fix this to make the program more robust.

Evaluation

Fitness for purpose

My testing demonstrates that my program meets the requirements of the specification and is therefore fit for purpose. It asks for the names of 6 people and stores them in an array. It also asks for their incomes and stores them in another array. The user can not input an income of 0 or less - they will be asked to re-enter. It works out if anyone is due a rebate based on their income being less than £18000. At the end the program displays all of the names and incomes which were input. It also displays the number of people who qualified for a rebate.

Robustness

My program is not particularly robust. If the user inputs any non-numerical value then it crashes. I think I could fix this using the IsNumeric function. However, it does ensure that only positive values can be input.

Efficiency

I think my program is quite efficient in its use of data structures - I have used arrays where appropriate, rather than lots of variables. This meant I was able to use a loop to traverse the arrays. If I had used variables then I wouldn't have been able to use a loop which would have resulted in more code.

Readability

I have used meaningful variable and array names so that their purpose is clear. I have used indentation and white space to help the various control structures or segments of code stand out. However, I have not put any internal commentary in - this would have improved readability massively and make it much easier to work out what the program is doing.