Section 5 - Mortgage Calculator Version 4

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

class MortgageData
{
private:
double dblPrincipal;
double dblRate;
double dblYears;

public:
// class constants
static const double MIN_LOAN;
static const double MAX_LOAN;
static const double MIN_RATE;
static const double MAX_RATE;
static const double MIN_YRS;
static const double MAX_YRS;

// accessors
bool setRate (double rt);
double getRate();
bool setPrincipal (double prin);
double getPrincipal();
bool setYears (double yrs);
double getYears();

// constructors
MortgageData(double prin, double rt, double yr);
MortgageData();
};

// static member intialization
double const MortgageData::MIN_LOAN = 1.;
double const MortgageData::MAX_LOAN = 100000000.;
double const MortgageData::MIN_RATE = .00001;
double const MortgageData::MAX_RATE = 25.;
double const MortgageData::MIN_YRS = 1;
double const MortgageData::MAX_YRS = 100;

// ordinary method prototypes
void stateInstructions();
void getInput(MortgageData &loan);
double computeMonthlyPayment(MortgageData loan);
void reportResults(double result);

// define the main method ---------------------

// the main method
int main()
{
double answer;
MortgageData loan;

stateInstructions();
getInput(loan);
answer = computeMonthlyPayment(loan);
reportResults(answer);
}


// stateInstructions method
void stateInstructions()
{
string instructions;
instructions =
"\nThe following program will calculate the \n"
"monthly payment  required for a loan of D dollars \n"
"over a period of Y years at an annual \n"
"interest rate of R%.\n";
cout << instructions;
}

// getInput method
void getInput(MortgageData &userData)
{
double dblResponse;

cout.setf(ios::fixed);
cout.precision(2);

// get principal
do
{
cout << "\nEnter amount of the loan. Only use numbers, \n"
"please.  No commas or characters like '$'.\n"
"Amount must be between " << MortgageData::MIN_LOAN
<< " and " << MortgageData::MAX_LOAN << ".\n"
"Your loan amount: ";
cin >> dblResponse;
}
while (!userData.setPrincipal(dblResponse));

// get interest
do
{
cout << "\nEnter the interest rate (If the quoted rate is 6.5%, \n"
"for example, enter 6.5 without the %.)\n"
"Rate must be between " << MortgageData::MIN_RATE
<< " and " << MortgageData::MAX_RATE << ".\n"
"Your annual interest rate: ";
cin >> dblResponse;
}
while (!userData.setRate(dblResponse));

// get length of loan
do
{
cout << "\nEnter term of the loan in years. \n"
"Term must be between " << MortgageData::MIN_YRS
<<  " and " << MortgageData::MAX_YRS << ".\n"
"Term of Loan: ";
cin >> dblResponse;
}
while (!userData.setYears(dblResponse));
}

// computeMonthlyPayment method
double computeMonthlyPayment(MortgageData loan)
{
// local variabls needed only in this method
double dblTemp, dblPmt, dblMonths, dblMoRt;

// convert years to months
dblMonths = loan.getYears() * 12;

// convert rate to decimal and months
dblMoRt = loan.getRate() / (100 * 12);

// use formula to get result
dblTemp = pow(1 + dblMoRt, dblMonths);
dblPmt = loan.getPrincipal() * dblMoRt * dblTemp
/ ( dblTemp - 1 );

// now that we have computed the payment, return it
return dblPmt;
}


// reportResults method
void reportResults(double result)
{
string signoff;
signoff =
"\nThanks for using the Foothill Mortgage Calculator. \n"
"We hope you'll come back and see us again, soon.\n\n";

cout.setf(ios::fixed);
cout.precision(2);
cout << "Your Monthly Payment: " << result << endl;

cout << signoff;
}

// define all MortgageData member methods ---------------------

// constructors
MortgageData::MortgageData()
{
// default values (can assign directly if preferred)
setPrincipal(MIN_LOAN);
setRate(MIN_RATE);
setYears(MIN_YRS);
}
MortgageData::MortgageData(double prin, double rt, double yr)
{
if (!setPrincipal(prin))
setPrincipal(MIN_LOAN);
if (!setRate(rt))
setRate(MIN_RATE);
if (!setYears(yr))
setYears(MIN_YRS);
}

// accessors
double MortgageData::getPrincipal()
{
return dblPrincipal;
}
double MortgageData::getRate()
{
return dblRate;
}
double MortgageData::getYears()
{
return dblYears;
}

// mutators
bool MortgageData::setPrincipal (double prin)
{
if (prin < MIN_LOAN || prin > MAX_LOAN)
return false;
dblPrincipal = prin;
return true;
}
bool MortgageData::setRate (double rt)
{
if (rt < MIN_RATE || rt > MAX_RATE)
return false;
dblRate = rt;
return true;
}
bool MortgageData::setYears (double yr)
{
if (yr < MIN_YRS || yr > MAX_YRS)
return false;
dblYears = yr;
return true;
}