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// File Name: Project9.cpp
// Author:
// Email Address:
// Assignment: Chapter 2 - Project 9
/* Description: Interest Calculator - User inputs item price, down payment amount, the interest rate (compounded monthly) and the
monthly payment amount. The program outputs the total amount of months to pay off the line of credit, the interest charged each
month, the last months charged interest, and the amount of the last payment */
// Last Changed: 10-5-12
#include <iostream>
using namespace std;
int main()
{
double principal; // Principal or loan amount
double interestRate; // Interest rate
double monthlyPayment; // Monthly payment
double interest = principal * (interestRate / 12); // Calculates monthly interest
double finalPayment; // Last months payment
double finalInterest; // Last months interest
double downPayment; // Down payment
double price; // Initial cost of item
int months; // Months
char exit; // Rerun program or exit program
cout.setf(ios::fixed); // Converts numbers into currency format
cout.setf(ios::showpoint); // Converts numbers into currency format
cout.precision(2); // Converts numbers into currency format
do // Always do this
{
months = 1; // Months value assigned to 1
cout << "Enter the cost of the item you wish to purchase: $"; // Prompts user to input the cost of the item
cin >> price;
cout << "Enter the down payment amount: $"; // Prompts user for the down payment amount
cin >> downPayment;
cout << "Enter the interest rate: "; // Prompts user for the interest rate
cin >> interestRate;
cout << "Enter the monthly payment: $"; // Prompts user to input the monthly payment amount
cin >> monthlyPayment;
principal = price - downPayment; // Calculates original principal or credit line amount
while (principal <= 0) /* If the principal amount is less than or equal to zero, do this. Prevents user from making the
down payment greater than the principal amount*/
{
cout << " " << endl; // Empty line for spacing
cout << "The down payment can not be greater than the price of the item." << endl; /* Tells the user that the item price
must be greater than the down payment */
cout << "Enter the cost of the item you wish to purchase: $"; // Prompts the user to enter the cost of the item
cin >> price;
cout << "Enter the down payment amount: $"; // Prompts user to enter the down payment amount
cin >> downPayment;
principal = price - downPayment; // Calculates original principal amount once correct inputs are entered by user
}
while(interestRate < 0) /* If user inputs an interest rate value below 0, the user will be asked to enter the interest
rate again. This prevents the user from having the program calculate a negative interest rate */
{
cout << " " << endl; // Empty line for spacing
cout << "The interest rate must be greater than zero." << endl;
cout << "Enter the interest rate: ";
cin >> interestRate;
}
while(monthlyPayment <= 0) /* If the user inputs a number less than or equal to zero for the monthly payment, do this.
This will prevent user from creating an infinite loop by entering 0 as the value for the monthly payment */
{
cout << " " << endl;
cout << "Monthly payment must be greater than zero." << endl;
cout << "Enter the monthly payment: $";
cin >> monthlyPayment;
}
if(interestRate >= 1) // If the user inputs an interest rate greater than 1(not in decimal form) do this
{
interestRate = interestRate / 100; // Converts interest from percentage form to decimal form
}
if(monthlyPayment >= principal) /* If the montly payment entered by user is equal to or larger than the principal amount
entered by user, do this. If the principal amount is lower than the monthly payment, this gives the correct output */
{
finalInterest = principal * (interestRate /12); // Calculates the final months interest
cout << " " << endl; // Empty line for spacing
cout << "MONTHS" << "\t" << "INTEREST" << "\t" << "PRINCIPAL" << endl; // Column Headers
cout << "------" << "\t" << "--------" << "\t" << "---------" << endl; // Column dividers
cout << months << "\t $" << finalInterest << "\t" "\t $" << principal << endl; /* Output: Count of months, monthly
interest and monthly principal. \t is used to tab columns for spacing */
cout << " " << endl; // Empty line used for spacing
cout << "Number of payments: " << months << endl; /* Output of the total number of payments or
the total number of months to pay off line of credit */
cout << "Last months interest: $" << finalInterest<< endl; // Output of last months interest
finalPayment = principal = principal * (1 + interestRate / 12); // Calculates the amount of the final payment
cout << "Last payment: $" << finalPayment << endl <<endl; // Ouputs final payment amount
cout << "Press Y to run again or any other key to exit: "; // Prompts user to rerun or exit the program
cin >> exit;
system("CLS"); // Clears screen
}
else // If the "if statement" above is false do this
{
interest = principal * (interestRate / 12); // Calculates interest
principal = principal * (1 + interestRate / 12) - monthlyPayment; // Calculates principal
cout << " " << endl; // An empty line for spacing
cout << "MONTHS" << "\t" << "INTEREST" << "\t" << "PRINCIPAL" << endl; /* Output of column headers:
MONTHS, INTEREST, and PRINCIPAl */
cout << "------" << "\t" << "--------" << "\t" << "---------" << endl; // Dashes to separate column header from output below
cout << months << "\t $" << interest << "\t" "\t $" << principal << endl; /* Output: Count of months, monthly interest, and
monthly principal */
while(principal > monthlyPayment) /* As long as the principal is greater than the monthly payment, do this. This prevents the
principal amount from becomming a negative number */
{
interest = principal * (interestRate / 12); // Calculates interest
principal = principal * (1 + interestRate / 12) - monthlyPayment; // Calculates principal
months = months++; // Counter for months
cout << months << "\t $" << interest << "\t" "\t $" << principal << endl; /* Output: Count of months, monthly interest, and
monthly principal */
}
cout << " " << endl; // Empty line for spacing
cout << "Number of payments: " << months+1 << endl; /* Adds 1 to months to give the total amount of months it took to pay
off debt*/
finalInterest = principal * (interestRate /12); // Calculates last months interest
cout << "Last months interest: $" << finalInterest<< endl; // Output of last months interest
finalPayment = principal * (1 + interestRate /12); // Calculates final payment
cout << "Last payment: $" << finalPayment << endl <<endl; // Output of final payment
cout << "Press Y to run again or any other character to exit: "; // Prompts user to run program again or exit
cin >> exit;
system("CLS"); // Clears screen
}
}
while(exit == 'y' || exit == 'Y'); /* If the user inputs Y or y for exit, the program runs again. Any other character ends the
program */
return 0;
}
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