Editing car loan calculator code

[llind212]

I am a beginner c++ student with an assignment to create a car loan calculator. I am having trouble with the calculations of the monthly payment, which I assume is because the operands are of different types in the equation? I am also not able to produce the results for the number of payments, total amount owed and total interest paid. If someone could look over my code, I would appreciate any input to help get my program working correctly!

//Date: 2/15/2011
// Programmer: Lindsay Lewis
// Description: This program computes the monthly payment for a car loan

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;

int main()
{

// This step requires the user to input the type of vehicle
string car_type;
cout << "Enter the type of vehicle: ";
getline (cin,car_type);

// This step requires the user to input the purchase price of the car
double purchase_price;
cout << "Enter the purchase price of the car: ";
cin >> purchase_price;

// This step requires the user to input the amount of the down payment
double down_payment;
cout << "Enter the amount of your down payment: ";
cin >> down_payment;

// This step requires the user to input the number of years to pay off the car
int years;
cout << "Enter the number of years to pay off the car: ";
cin >> years;

// This step requires the user to input the interest rate
float interest_rate;
cout << "Enter the annual interest rate:";
cin >> interest_rate;

// This step calcuates the interest rate
double interest;
interest = interest_rate / 100;


// This step defines the value for the amount to be financed
double amount_financed;
amount_financed = purchase_price - down_payment ;

// This step defines the number of payments per year
int payments_year;
payments_year = 12;

// This step calculates the monthly payment
double monthly_payment;
monthly_payment = (amount_financed * (interest / payments_year)) /(1 - pow(1+\
interest / payments_year),(-payments_year * years));

// This step calculates the number of payments
double number_payments;
number_payments = years - monthly_payment;

// This step calculates the total amount owed
double total_amount_owed;
total_amount_owed = number_payments * monthly_payment;

// This step calculates the total interest paid
double total_interest_paid;
total_interest_paid = monthly_payment * number_payments - amount_financed;

// This step calculates the number of payments
double number_payments;
number_payments = years - monthly_payment;

// This step calculates the total amount owed
double total_amount_owed;
total_amount_owed = number_payments * monthly_payment;

// This step calculates the total interest paid
double total_interest_paid;
total_interest_paid = monthly_payment * number_payments - amount_financed;

cout << left;
cout << setw(40) << "Monthly Car Loan Payment Calculation" << endl;
cout << setw(40) << "========================================" << endl;
cout << setw(40) << "Type of Vehicle:" << car_type << endl;
cout << setw(40) << "Purchase Price:" << purchase_price << endl;
cout << setw(40) << "Down Payment:" << down_payment << endl;
cout << setw(40) << "Amount Financed:" << amount_financed << endl;
cout << setw(40) << "Length of Loan:" << years << endl;
cout << setw(40) << "Annual Interest Rate:" << interest_rate << endl;
cout << setw(40) << "Monthly Payment:" << monthly_payment << endl;
cout << setw(40) << "Number of Payments:" << number_payments << endl;
cout << setw(40) << "Total Amount Owed:" << total_amount_owed << endl;
cout << setw(40) << "Total Interest Paid:" << total_interest_paid << endl;

}

[moorecm]

To debug this yourself, you could just print out the values of the variables as you go along and verify that they are correct. Then you can narrow it down to a line where a calculation goes wrong.

Most likely, there's integer division in there somewhere and some floating point calculation isn't returning what you'd expect. Just a guess, though.

[Toothkiller]

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;

int main()
{

// This step requires the user to input the type of vehicle
string car_type;
cout << "Enter the type of vehicle: ";
getline (cin,car_type);

// This step requires the user to input the purchase price of the car
double purchase_price;
cout << "Enter the purchase price of the car: ";
cin >> purchase_price;

// This step requires the user to input the amount of the down payment
double down_payment;
cout << "Enter the amount of your down payment: ";
cin >> down_payment;

// This step requires the user to input the number of years to pay off the car
int years;
cout << "Enter the number of years to pay off the car: ";
cin >> years;

// This step requires the user to input the interest rate
float interest_rate;
cout << "Enter the annual interest rate:";
cin >> interest_rate;

// This step calcuates the interest rate
double interest;
interest = interest_rate / 100;


// This step defines the value for the amount to be financed
double amount_financed;
amount_financed = purchase_price - down_payment ;

// This step defines the number of payments per year
int payments_year;
payments_year = 12;

// This step calculates the monthly payment
double monthly_payment;
monthly_payment = (amount_financed * (interest / payments_year)) /(1 - pow(1+\
interest / payments_year),(-payments_year * years));

// This step calculates the number of payments
double number_payments;
number_payments = years - monthly_payment;

// This step calculates the total amount owed
double total_amount_owed;
total_amount_owed = number_payments * monthly_payment;

// This step calculates the total interest paid
double total_interest_paid;
total_interest_paid = monthly_payment * number_payments - amount_financed;

// This step calculates the number of payments
double number_payments;
number_payments = years - monthly_payment;

// This step calculates the total amount owed
double total_amount_owed;
total_amount_owed = number_payments * monthly_payment;

// This step calculates the total interest paid
double total_interest_paid;
total_interest_paid = monthly_payment * number_payments - amount_financed;

cout << left;
cout << setw(40) << "Monthly Car Loan Payment Calculation" << endl;
cout << setw(40) << "========================================" << endl;
cout << setw(40) << "Type of Vehicle:" << car_type << endl;
cout << setw(40) << "Purchase Price:" << purchase_price << endl;
cout << setw(40) << "Down Payment:" << down_payment << endl;
cout << setw(40) << "Amount Financed:" << amount_financed << endl;
cout << setw(40) << "Length of Loan:" << years << endl;
cout << setw(40) << "Annual Interest Rate:" << interest_rate << endl;
cout << setw(40) << "Monthly Payment:" << monthly_payment << endl;
cout << setw(40) << "Number of Payments:" << number_payments << endl;
cout << setw(40) << "Total Amount Owed:" << total_amount_owed << endl;
cout << setw(40) << "Total Interest Paid:" << total_interest_paid << endl;

}

use code tags.

The answers to your questions are mostly mathematical. Like to find number of payments do this:

int numberofpayments=0;
while(amountowed>0)
{
        amountowed-=payment;
        numberofpayments++;
}

and if you are really confused about types such as double and int interacting just play around with them making programs to see what happens when you plug them in.

[kernalSeiden]

Are they teaching you functions in your programming class yet? This program would benefit a lot from the use of functions; would make for much prettier code at the very least.

edit: and by the way, put before and after your code when posting.

[llind212]

We have not yet covered code tags or functions in the programming class yet. I'm sorry to say that I do not have any clue as to how to use code tags. Thanks for the input though!

[danaigo]

in this forum when you post there is a format box to the right. make sure your cursor is on a new line and then click the <> button you will get a [] with the word code in it and a closing tag with the word /code in it. Put the code you want us to look at in between the two tags.

that will make your code appear like this:

//your code goes here. 

[moorecm]

Also note the preview button, so that you can play with it before posting.