initialize class functions but output still 0 - c++

Question

I am having problems with this program. When I compile it, I intialize all of the variables based upon the users input, but the cout still shows that the problem has '0' for most of the statements and for one of the statements its a '-negative' number. Any thoughts?
#include <iostream>
#include <conio.h>
#include <cmath>
#include <stdexcept>
using namespace std;
class MortgageCalc
{
protected:
float term;
public:
void setData(float, float, float);
float setTerm ();
float monthly;
float total;
float interest;
int years;
float loan;
};
void MortgageCalc::setData(float l, float i, float y)
{
loan = l;
interest = i;
years = y;
setTerm();
}
float MortgageCalc::setTerm()
{ //simple interest calculation with power calc to establish whole number translation
term = pow((1 + ((interest/100) / 12)), (12 * years));
return term;
}
class mPayment : public MortgageCalc
{
public:
int monthly()
{
return ((loan * ((interest/100) / 12) * term ) / (term - 1));
}
};
class tPayment : public mPayment
{
public:
int total()
{
return (monthly() * (years * 12));
}
};
class iPayment : public tPayment
{
public:
int plusInterest()
{
return (total() - loan);
}
};
int main()
{
double loan(0), interest(0);
int years = 0;
MortgageCalc mort1;
cout << "Enter the total loan amount on your mortgage loan: $"; //established loan variable
cin >> loan;
cout << "Enter the interest rate (in whole #'s only): "; //establishes interest rate variable
cin >> interest;
cout << "Enter the length of the loan in years: "; //establishes term of payments
cin >> years;
mort1.setData(loan, interest, years);
mPayment m;
cout << "Monthly payment due is " << m.monthly() << "." << endl;
tPayment t;
cout << "Total payment will be " << t.total() << "." << endl;
iPayment i;
cout << "Total payment plus Interest will be " << i.plusInterest() << "." << endl;
return 0;
};

Answer 1

You are taking all different objects like MortgageCalc mort1; mPayment m; tPayment t; iPayment i;.
These object do not have any relation.
Example:
mort1 = {term, monthly, total, interest, years, loan}
and suppose you have initialize with 1
mort1 = {term=1, monthly=1, total=1, interest=1, years=1, loan=1}
but it doesnot impact to the m because both are stored in memory on different location.
m = {term=0, monthly=0, total=0, interest=0, years=0, loan=0}
You can check both have different base address like cout<<&mort1<<endl<<&m; .
Data member you have set is part of MortgageCalc mort1 instead of mPayment m; tPayment t;.
You need to brush up your C++ basic's.

Answer 2

You use default constructors on those lines:
mPayment m;
tPayment t;
iPayment i;
They have no notion of previously input data held in mort1. You did not take care for any way to "share" or "communicate" this data.
m,t,i were all initialized with random data. There is no relation to mort1.
I won't go into details of what correct architecture here would be, but you should read about base class initialization. As a hint I'd say in your (a little weird) example you could try making this syntax work:
mPayment m(mort1);