Private Variable Question

[skyline01]

I have a question about private class attributes. I have the following program to calculate the yield-to-maturity for a coupon-paying bond:

Bond.h:

#ifndef BOND_H_
#define BOND_H_
class bond {
public:
	bond(); // default constructor

	void set_YTM(double YTM0); // setter
	double get_YTM(); // accessor

	// variables:
	double T; // time to maturity
	double t; // current time
	double C; // annual coupon payment
	double P; // principal

	// methods:
	double price_calculator(); // calculates the price of a bond

private:
	double YTM; // yield-to-maturity (uses continuous compounding)
};
#endif 

Bond.cpp:

#include "Bond.h" // use the Bond header file
#include <assert.h>
#include <math.h>

// default constructor
bond::bond()
{
	Price = 0;
	YTM = 0;
}

// since YTM is private, we need to set and get the yield-to-maturity:

void bond::set_YTM(double YTM0)
{
	assert(YTM0 >= 0);
	YTM = YTM0;
}

double bond::get_YTM()
{
	return YTM;
}

// calculate the bond price, given YTM, T, t, C, and P:
double bond::price_calculator()
{
	// do the sum:
	double sum;
	for(int i = 1; i <= T; i++)
	{
		sum = sum + exp(-(i - t)*YTM);
	}
	return C*sum + P*exp(-(T - t)*YTM);
}

Main.cpp:

#include <iostream>
#include "Bond.h"
using namespace std;

int main(void)
{
	bond bond1; // call the default constructor of a bond
	cout << "We will calculate the price of a bond given its YTM." << endl;

/*
	cout << "Enter the time to maturity (years) of the bond when issued (T): ";
	cin >> bond1.T;
	cout << "Enter the current time (t): ";
	cin >> bond1.t;
	cout << "Enter the coupon payment (C): ";
	cin >> bond1.C;
	cout << "Enter the principal payment (P): ";
	cin >> bond1.P;
	cout << "Enter the yield-to-maturity (YTM): ";
	double YTM_dummy;
	cin >> YTM_dummy;
	bond1.set_YTM(YTM_dummy);
*/

	bond1.T = 4;
	bond1.t = 0.1;
	bond1.C = 5;
	bond1.P = 100;
	bond1.set_YTM(0.05);

	cout << "Price is: " << bond1.price_calculator() << endl;

	return 0;
}

In main, I am trying 2 ways to send in the variables into the bond1 class. In the first way (which I have commented out), I assign the values through cin's. In the second way, I hard-code them into the class. The second way works. But, I don't understand why the first way does not work (this is the way that I want, though). Any ideas? Thanks!

[Zhuge]

What was the error when you tried the first method?

[IceThatJaw]

Whats the problem exactly? I ran it and T, t, C, and P were strored correctly.

Is it

	cout << "Enter the yield-to-maturity (YTM): ";
	double YTM_dummy;
	cin >> YTM_dummy;
	bond1.set_YTM(YTM_dummy);

that is giving you problems?


The cin part isn't what giving you problems, it must be your logic in the implementation of bond.

[skyline01]

The problem is that my bond price calculator function returns "nan" (i.e., not a number). I don't know why it's happening.

[IceThatJaw]

I want to help you but whats up with this?

bond::bond()
{
	Price = 0;
	YTM = 0;
}

Price isn't even a declared variable.

[skyline01]

Oops. Sorry about that. I meant to remove Price from that default constructor. (I basically boiled my code down to the core stuff. I have a bunch of other stuff in my program that I know works, but it isn't necessary for the given issue.)

[ne555]

-Wall

double bond::price_calculator()
{
	// do the sum:
	double sum;
	for(int i = 1; i <= T; i++)
	{
		sum = sum + exp(-(i - t)*YTM); //warning: ‘sum’ is used uninitialized in this function 
	}
	return C*sum + P*exp(-(T - t)*YTM);
}

[skyline01]

That's it! Thanks! I forgot to initialize sum to 0 before the loop started.