Faculty of Science and Technology
4483 Software Technology 1 and
8995 Software Technology 1 G
Semester WT, 2019
Marked Tutorial
(5% of grade Optional Assignment)
The House Cost Calculator
GENERAL INSTRUCTIONS
This assignment should be done individually. The assignment consists of writing a program and demonstrating it.
This assignment is marked by demonstration if you can’t complete it on time (i.e. week 5, then show your tutor what you have done and then do a resubmission week 6). Resubmissions will be allowed until end of week 6. I encourage all students to aim for 5/5 for this mini assignment.
Your tutor, will mark the assignment demonstration that you will give. One purpose of the demonstration is for other students to watch, learn and become inspired. Your tutor, can ask you to explain your code as a check that you wrote the assignment yourself.
I strongly suggest that you build the assignment over the weekend or in the evenings – it’s likely that a twohour tutorial is not long enough for a student to complete the assignment to a satisfactory level.
Students can work at different levels according to their preferences; the grade you will achieve will depend on the functionality of the submitted program as shown in the marking rubric later in this document. If you are pressed for time skip the Investor report (only 1 mark)
You can ask for help in the tutorials and at PALS, but nobody should do the assignment for you (this is your chance to learn programming on a more realistic problem than the tutorials).
In many ways this is a practice Assignment – the assignment is of similar difficulty, here is a chance to practice and get help so you can confidently attack the main assignment.
MT1 Briefing:
Important NOTE: For MT1 you do not need to allow for input of nonnumeric in numeric inputs. My test cases will not include things like entering ‘fred’ in the ‘cost of property’ field. So, you don’t need to use exceptions (but you will need to do this in the main assignment due week 7)
Here in Australia the housing market is divided into mainly 2 kinds of purchasers.
 First Home Buyers
 Investors
The system you need to build helps both kinds of customers with different reports by providing the following services:
 For first home buyers it will give them a report on how much they need to pay each month as a repayment;
 For investors it will report if the property is positive or negative cash flow;
The Current Interest Rates are:
Bank  Loan Type  Interest Rate  Loan Establishment fee  Max percent able to be borrowed 
WESTPAC  HOME  3.79%  395  80% 
WESTPAC  INV  3.89%  395  95% 
COMB  HOME  3.79%  600  95% 
COMB  INV  3.99%  600  95% 
ANZ  HOME  3.69%  600  95% 
ANZ  HOME2  3.63%  600  80% 
NAB  HOME  3.54%  790  95% 
NAB  INV  4.86%  0  95% 
BEYOND  HOME2  3.79%  0  95% 
Loan Term in Years is 30 years (or 30*12 months = 360 months, 360 Payments)
NOTE1: The above rates and information is based on reality but is not reality, its simplified for the assignment. Banks have all kinds of varying terms and conditions to make it hard to compare one bank with another.
NOTE2: Westpac and NAB do not actually have a loan establishment fees as shown. I am using it as an approximation for the assignment, the above table is not a reflection of reality it’s a firstyear assignment example.
The program must have
 A clear easy to use main menu with an exit
 Displays the table above, called the “rates report”.
 It produces a report “First Home Buyer report” for a first home buyer of what they will repay each month.
 It produces a ‘Investor report’ for an investor what they will pay each and using the weekly rent as input if it is cashflow negative or positive.
 Note also that some input errors should be detected specifically:
 Bank codes must be WESTPAC, COMB, ANZ, NAB, BEYOND (or the relevant subset)
 Cost of property must be between 150,000 and 1,000,000
 Loan type must be INV, HOME, HOME2 (or the relevant subset)
 Deposit must be between 0 and the cost of the property
 The rent must be between $100 to $1000
 NOTE/WARNING – On my marking sheet test cases will check some of this editing
Calculation of First Home buyer repayments
Before we can calculate the repayments there are a few inputs needed:
 the cost of the property
 The bank
 The loan type (Home or Home2)
 The amount of deposit
Also, in the ACT a $7,000 grant is given to new home buyers; this needs to be added to the deposit (assume this program is for the ACT only).
We are ignoring stamp duty which is low for first home buyers
Step  Action  Notes 
1  input and check The cost of the property  Range 150,000 to 1,000,000 
2  input and check The bank code  WESTPAC, COMB, etc. 
3  input and check loan type  INV, HOME, HOME2 
4  input and check amount of deposit  Range 0 to cost of property 
5  Add 7000 to deposit to give final deposit  
6  Add loan establishment fee to cost of property giving amount needed  
7  Subtract final deposit from amount needed giving amount of loan  
8  Compute % being loaned (amount of loan)/(cost of the property)*100
 
9  Check that the loan is for less than or equal to the max % that can be borrowed  If not print a message and return to menu 
10  Convert the % interest rate to a decimal  Eg 3.71% would become 0.0371 
11  Use the supplied formulae to find the monthly repayments  This is the method ‘calcMonthPayment’ 
12  Display all the details – see example run  
Example Calculation: (WESTPAC HOME 3.79% 395 80%)
Step  Action  Notes 
1  input and check The cost of the property  300,000 
2  input and check The bank code  WESTPAC 
3  input and check loan type  HOME 
4  input and check amount of deposit  50,000 
5  Add 7000 to deposit to give final deposit  57,000 
6  Add loan establishment fee to cost of property giving amount needed  300,395 
7  Subtract final deposit from amount needed giving amount of loan  300,39557,000 = 243,395 
8  Compute % being loaned (amount of loan)/(cost of the property)*100  243,395/300,000 = 0.8113 =81.13 
9  Check that the loan is for less than or equal to the max % that can be borrowed  81.13 < 80 (false)
print a message and return to menu 
10  Convert the % interest rate to a decimal  
11  Use the supplied formulae to find the monthly repayments  
12  Display all the details – see example run 
Example Calculation: (WESTPAC HOME 3.79% 395 80%)
Step  Action  Notes 
1  input and check The cost of the property  300,000 
2  input and check The bank code  WESTPAC 
3  input and check loan type  HOME 
4  input and check amount of deposit  60,000 
5  Add 7000 to deposit to give final deposit  67,000 
6  Add loan establishment fee to cost of property giving amount needed  300,395 
7  Subtract final deposit from amount needed giving amount of loan  300,39567,000 = 233,395 
8  Compute % being loaned (amount of loan)/(cost of the property)*100  233,395/300,395 = 0.77798 =77.80 
9  Check that the loan is for less than or equal to the max % that can be borrowed  77.80 < 80 (true)

10  Convert the % interest rate to a decimal  3.79 becomes 0.0379 
11  Use the supplied formulae to find the monthly repayments  repay = calcMonthPayment(0.0379, 233395,30);
Calculated in Excel this is ($1,086.19) 
12  Display all the details – see example run 
Calculation of Investor Report
Before we can calculate the repayments there are a few inputs needed:
 the cost of the property
 The bank
 The loan type (Home or Home2)
 The amount of deposit
 The expected weekly rent
Also for cash flow purposes:
 The rent received is typically for 50 weeks (not 52 – this allows for 2 weeks of vacancy)
 10% of the rent goes to the renting agent
 Roughly 4% of the rent goes on maintenance
 About 6% of the rent goes in land tax, rates and other holding costs
 We are ignoring stamp duty which is not low for Investors but its complicated so to keep it simple we ignore it.
Step  Action  Notes 
First do the cost calculation  
1  input and check The cost of the property  Range 150,000 to 1,000,000 
2  input and check The bank code  WESTPAC, COMB, etc. 
(3)  Loan type will be INV  
4  input and check amount of deposit  Range 0 to cost of property 
5  Input and check weekly rent  Range $100 to $1000 
6  Add loan establishment fee to cost of property giving amount needed  
7  Subtract final deposit from cost of the property giving amount of loan  
8  Compute % being loaned (amount of loan)/(cost of the property)*100
 
9  Check that the loan is for less than or equal to the max % that can be borrowed  If not print a message and return to menu 
10  Convert the % interest rate to a decimal  Eg 3.71% would become 0.0371 
11  Use the supplied formulae to find the monthly repayments  This is the method ‘calcMonthPayment’ 
Now we do the Income Calculation  
12  Take the weekly rent multiply by 50 giving gross rent  
13  Now multiply the gross rent by 0.8 giving gross income  10%+4%+6% = 20% 100%20% = 80% 80% >> *0.8 
14  Now divide the gross income by 12 giving monthly income  
Now we do the Cashflow Calculation  
15  Subtract the monthly repayments from monthly income to give monthly cash flow  
16  Display all the details – see example run  
Example Calculation: (WESTPAC INV 3.89% 395 95%)
Step  Action  Notes 
1  input and check The cost of the property  500,000 
2  input and check The bank code  WESTPAC 
(3)  Loan type input not needed will be INV  
4  input and check amount of deposit  45,000 
5  Input and check weekly rent  $530 
6  Add loan establishment fee to cost of property giving amount needed  500,395 
7  Subtract deposit from amount needed giving amount of loan  500,39545,000 = 455,395 
8  Compute % being loaned (amount of loan)/(cost of the property)*100  455,395/500,395 = 0.9100 =91.00 
9  Check that the loan is for less than or equal to the max % that can be borrowed  91.00 < 95 (true)

10  Convert the % interest rate to a decimal  3.89 becomes 0.0389 
11  Use the supplied formulae to find the monthly repayments  repay = calcMonthPayment(0.0389, 455395,30);
Calculated in Excel this is: ($2,145.35) 
Now we do the Income Calculation  
12  Take the weekly rent multiply by 50 giving gross rent  530*50 = 26,500 
13  Now multiply the gross rent by 0.8 giving gross income  26500*0.8 = 21,200 
14  Now divide the gross income by 12 giving monthly income  21,200/12=1,766.66 
Now we do the Cashflow Calculation  
15  Subtract the monthly repayments from monthly income to give monthly cash flow  1,766.662,145.35 = 378.69
Yep in this case you lose 378.69 dollars a month 
16  Display all the details – see example run 
Notes
During my testing I found small rounding errors were affecting the result. Consequently, I will allow minor rounding errors in the answer (about 1c).
The Excel PMT function can help in the creation of test data
The following formulae will give the repayments on a loan of $20,000 over 3 years at 5%
=PMT(0.05/12,3*12,20000) The correct answer is 599.42
This website seems to use the same formula as me (as detailed below) accurate to the nearest cent: It may help in testing.
The formula I used can be found on Wikipedia. Most students don’t need this level of detail but it’s here for the curious.
https://en.wikipedia.org/wiki/Amortization_calculator
double calcMonthPayment(double yearlyrate, double loan, int years)
{
/* Inputs to this routine are:
yearlyrate – the yearly interest rate as a decimal
(eg a 5% interest rate would be entered as 0.05)
loan – the amount of the loan in dollars and cents (eg 21210.90)
years – an integer indicating the years of the loan (eg 3 )
*/
double retv;
int payments;
double mul;
double rate;
rate = yearlyrate / 12;
payments = years * 12;
mul = Math.pow(1 + rate, payments);
retv = (loan * mul * rate) / (mul – 1);
return retv;
}
I provide some code as follows:
I provide a Banks class that has been reasonably tested to assist you. It comes with some examples from the lecture.
I provide a menu example which uses a do while loop and has two options A and B (as well as an exit)
The following code is how I input the deposit amount
System.out.printf(“\nEnter Deposit: “);
double dep = in.nextDouble();
String temp = in.nextLine(); // eat whitespace
The following code is how I input bank code
System.out.printf(“\nEnter Bank Id: “);
String ban = in.nextLine();
//ban=ban.trim().toUpperCase();// you may want this
Students can change all the object/class models that I supply (there are better ones, but as it’s presented, it’s easy for beginners).
I give you this code so you can use it (i.e. its ok to copy and or modify the supplied code).
How to Get Started
This may look daunting but its designed to be done in baby steps – each small piece within your grasp (about 27 small steps – each one as simple (I hope) as a tutorial).
Beginner students should start with the following process:
 Read the assignment through carefully
 I mean it – Read the assignment through carefully; try to understand it
 Produce a test plan – not a huge formal one but calculate a few examples (as I do above, say 3 new First homebuyers and 3 new Investor reports). This process ensures you understand the maths of how to do it (use the PMT function in excel, I supply a spreadsheet)
 Load the menu example run it try to understand it
 Modify it so its suitable for the assignment and the exit works (this is worth 1 mark)
 Try to code the Rates Report if possible, using supplied Banks Class – if not like print hello (this is worth 1 mark)
 Then code the First Homebuyers report it’s the most straightforward (this is worth 2 marks)
 First get the menu option working
 Then code the input routine for cost of property (check range)
 Then code the input routine for bank code and check it
 Code the input routine for loan type
 Code the input routine for inputting deposit
 Do the calculations (will involve declaring new variables)
 Do the 15 or so lines of code to print the answer (and all other variables shown in the example) out.
 Tidy it up so its neatly formatted
 Then code the Investor report (this is worth 1 mark)
 Use basically the same steps as the First home buyers plus the extra input and computation.
 Test all options thoroughly (this stops mark deductions for things wrong)
 Show it to your tutor who will have a test sheet to work through with you and allocate a mark.
 If the mark is low and you think you can improve on it, then fix the problem and resubmit it in week 6.
Marking Rubric
Marks  Feature 
0  No submission till too late (once I have gone through the answer in the lecture in week 10 we can’t mark any more) 
1  Your menu works and exits 
+1  the Rates Report works and is nicely formatted 
+2  The First Home Buyer Report works and is nicely formatted 
+1  the Investor report works and is nicely formatted 
0.5  Poor formatting or minor accuracy error 
0.5  minor accuracy error 
0.5  input not edited – WARNING (this will NOT include putting letters in numeric fields) 
0.5  the menu fails to loop 
0.5  Additional failings as identified by your tutor 
Example Runs
Menu Exit
Rates Report
First Home Buyers
Investment Loan
Error Case 1 Borrow To high a percentage
Error case 2 ANZ has no INV loan type
Error case 3 Deposit is out of range
Error case 4 – cost numbers negative or to big
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