Section 2 - Mortgage Calculator Version 3

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

// method prototypes
void stateInstructions();
void getInput();
double computeMonthlyPayment();
void sayGoodbye();

// global variables shared by more than one method
double dblPrincipal, dblRate, dblYears;

int main()
{
double answer;

stateInstructions();
getInput();
answer = computeMonthlyPayment();
cout <<  "\nYour Monthly Payment: " << answer << endl;
sayGoodbye();
}

// gives an overview to user
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;
}

// gets input, stores in globals
void getInput()
{
string prompt;

// get principal
prompt = "\nEnter amount of the loan. (only use numbers, \n"
"please, no commas or characters like '$')\n"
"Your loan amount: ";
cout << prompt;
cin >> dblPrincipal;

// get interest
prompt = "\nNow enter the interest rate (If the quoted rate is 6.5%, \n"
"for example, enter 6.5 without the %.)\n"
"Your annual interest rate: ";
cout << prompt;
cin >> dblRate;

// get length of loan
prompt = "\nEnter term of the loan in years: ";
cout << prompt;
cin >> dblYears;
}

// computes and returns answer
double computeMonthlyPayment()
{
double dblTemp, dblPmt, dblMoRt, dblMonths;

// convert years to months
dblMonths = dblYears * 12;

// convert rate to decimal and months
dblMoRt = dblRate / (100 * 12);

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

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


// sign off
void sayGoodbye()
{
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 << signoff;
}