Below is my code to calculate interest and balances and how many months to get there. However, my months calculations are way off by the thousands. Any idea?

#include<iostream>
#include<string>
#include<cmath>

using namespace std;

class Account
{
        public:
        Account();
        Account (double bal);
        void deposit(double amount);
        void withdraw(double amount);
        double get_balance() const;
        void add_interest(double rate);

        private:
        double balance;
};

Account::Account()
{
}
Account::Account(double bal)
{
        balance = bal;
}

void Account::deposit(double amount)
{
        balance +=amount;
}

void Account::withdraw (double amount)
{
        if ( balance >= amount)
                balance -= amount;
        else
                balance -= 5.00;  // Charge a $5.00 penalty fee if attempting to withdraw more than balance.
}

double Account::get_balance()const
{
        return balance;
}

void Account::add_interest(double rate)
{
        balance *= ( 1 + (rate/100.0));
}

int main()
{

        cout << " Enter initial investment: ";
        double initial_investment;
        cin >> initial_investment;

        cout << " Enter annual interest rate in percentage: ";
        double rate_in_percentage;
        cin >> rate_in_percentage;

        double monthly_rate = rate_in_percentage/100.0/12.0;
        double final_amount = 2 * initial_investment;

        Account my_account(initial_investment);

        int months = 1;

        //
        // one iteration of the loop corresponds to one month
        //

        while ( my_account.get_balance()<final_amount)
        {
                my_account.add_interest(monthly_rate);
                months++;
        }

        cout << " It took " << months << " months for $ " << initial_investment <<
                " to double at " << rate_in_percentage << "% annual interest. \n";

        cout << " Account balance: " << my_account.get_balance() << "\n";

        return 0;
}

Edited 3 Years Ago by diafol: fixed formatting

Show us the values you are entering and your output..

Below is the values and the output:

[hs001@cs hs001]$ g++ p6-5.cpp
[hs001@cs hs001]$ a.out
Enter initial investment: 1000
Enter annual interest rate in percentage: 5
It took 16637 months for $ 1000 to double at 5% annual interest.
Account balance: 2000.01
[hs001@cs hs001]$

Below is the values and the output:

[hs001@cs hs001]$ g++ p6-5.cpp
[hs001@cs hs001]$ a.out
Enter initial investment: 1000
Enter annual interest rate in percentage: 5
It took 16637 months for $ 1000 to double at 5% annual interest.
Account balance: 2000.01
[hs001@cs hs001]$

Now here is what the correct output should be. the professor supplied the main program but I had to create the class to work with his main program. I am not getting the correct output yet.


Enter initial investment: 1000
Enter annual interest rate in percentage: 5
It took 168 months for $1000 to double at 5% annual interest.
Account balance: 2002.48

figured it out. the calculation for the add_interest member function was wrong. It should have been


balance*= (1 + (12*(rate/12.0)));

thanks.

Show us the values you are entering and your output..

figured it out. the calculation for the add_interest member function was wrong. It should have been


balance*= (1 + (12*(rate/12.0)));

thanks.

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