C言語とC++言語コミュの英語なのですがこの課題に助けをください。

課題はこの以下です。
Your program will ask the user to enter the amount of
money they want to borrow, the interest rate, and the
monthly payment amount. Your program will then
determine how many months it will take to pay off that
loan, what the final payment amount will be, and how
much interest was paid over that time. If the monthly
payment amount isn't high enough to pay off more than
one month's interest, your program should notify the
user what the minimum monthly payment is.

Here are some examples of how your program should
behave. Please use the exact same test cases as these,
so that I can verify that your program works:

** Welcome to the Consumer Loan Calculator **

How much do you want to borrow? $1000
What is the annual interest rate expressed as a
percent? 18
What is the monthly payment amount? $50
Your debt will be paid off after 24 months, with a
final payment of just $47.83
The total amount of interest you will pay during that
time is $197.83

** Don't get overwhelmed with debt! **


** Welcome to the Consumer Loan Calculator **

How much do you want to borrow? $15000
What is the annual interest rate expressed as a
percent? 10
What is the monthly payment amount? $100
You must make payments of at least $126
Because your monthly interest is $125.00

** Don't get overwhelmed with debt! **


** Welcome to the Consumer Loan Calculator **

How much do you want to borrow? $-50
You must enter a positive number!
How much do you want to borrow? $-200
You must enter a positive number!
How much do you want to borrow? $20000
What is the annual interest rate expressed as a
percent? -2.5
You must enter a positive number!
What is the annual interest rate expressed as a
percent? 5
What is the monthly payment amount? $0
You must enter a positive number!
What is the monthly payment amount? $200
Your debt will be paid off after 130 months, with a
final payment of just $125.79
The total amount of interest you will pay during that
time is $5925.79

** Don't get overwhelmed with debt! **

Here are the rules and some tips:
○The user enters the interest rate as an annual
percentage rate. You need to convert this annual
percentage to a monthly decimal. For example, 12%
annual interest is 1% per month, which is 0.01
○Your program must allow only positive numbers to be
entered by the user, as shown above
○This program should mimic the standard way loans work for credit cards, car loans, and home mortgages: Each
month the following happens:
・The balance (amount owed) is multiplied times the
monthly interest rate to determine how much interest is owed this month. This amount of interest is added to
the principle (additional debt)
・This amount of interest is also added to the total
interest so far (to be output at end)
・The monthly payment is subtracted from the balance,
reducing the amount of debt.
・The month is counted (to be output at end)
This is repeated each month until the debt is paid off (balance reaches zero).
○Your program must notify the user if their monthly
payment isn't high enough, and tell them what the
minimum payment is to pay off one month's interest (and thus make progress paying off the debt).
○Your program must use at least 2 functions in
addition to main. At least one of these functions must
use a call-by-reference parameter These functions can
be of your choosing, but here are two ideas for
functions you could write for your program:
void get_input(double& principle, double& interest, double& payment);
/* This function asks the user to input the
principle, interest, and payment amount, and only
accepts positive numbers for input. All three
parameters are call-by-reference, so the function in
effect returns the three values by changing the values
of the arguments which are passed to it. The initial
values of these parameters are ignored and overwritten.
*/

double pay_off_loan(double principle, double rate,
double payment,int& months, double& total_interest);
/* This function assumes the payment is enough to
cover first month's interest. It has a loop to pay off the loan one month at a time.
Pre-Condition:
principle = starting principle.
rate = monthly interest rate expressed as a
decimal.
payment = amount of monthly payment, which
must be high enough to pay off the first month's
interest.
Post-Condition:
amount of final payment is returned by the
function.
months = number of months it took to pay off
loan.
total_interest = total amount of interest
paid during that time.
It may help to think of principle, rate, and
payment as input parameters, and months, and
total_interest
as output parameters.
*/