static data member help

[hoosier23]

any idea what i am doing wrong?

Error 3 error LNK2001: unresolved external symbol "private: static float SavingsAccount::annualInterestRate" (?annualInterestRate@SavingsAccount@@0MA) Savings.obj

SavingsAccount.h

#ifndef SAVINGSACCOUNT1_H
#define SAVINGSACCOUNT1_H

using namespace std;

class SavingsAccount 
{
private:
    static float annualInterestRate;
    float savingsBalance;
public:
    SavingsAccount()
    {
      annualInterestRate = 0.03;
      savingsBalance= 2000;
    }
    float calculateMonthlyInterest()
    {
        float subtotal = 0;
        float monthlyint = 0;
        subtotal = savingsBalance * annualInterestRate;
        monthlyint = subtotal / 12;
        savingsBalance = monthlyint + savingsBalance;
        return savingsBalance;
    }
    static void modifyInterestRate()
    {
        annualInterestRate=.04;
    }
    void printSavingsBalance()
    {
        cout << "Your balance is: $" << savingsBalance << endl;
    }
};
#endif

Savings.cpp

#include <iostream> 
#include "SavingsAccount.h"

using namespace std;

int main()
{
SavingsAccount saver1;        //instantiate saver1;
SavingsAccount saver2;        //instantiate saver2;

saver1.printSavingsBalance();
cout << "Interest of Month #1" << saver1.calculateMonthlyInterest() << endl;
saver1.modifyInterestRate();
cout << "Interest of Month #2" << saver1.calculateMonthlyInterest() << endl;

return 0;
}

any help would be great

:o

[Salem]

Why did you make it static?

It makes ALL the accounts have the same annual interest rate, and that's simply not true in the real world.

You need this just before your main

float SavingsAccount::annualInterestRate = 0;

> using namespace std;
Putting this in a header file is very bad form.
Anyone who includes the file will get the whole namespace whether they like it or not.

[hoosier23]

I had to make this static as if it were a fixed interest rate that a person is locked into. What is the logic behind using

float SavingsAccount::annualInterestRate = 0;
right before my main? I see that you are setting annualInterestRate to zero, but why does this need to be done? Afterall, I have made annualInterestRate .03 in the default constructor.

Thank you s.o.s.

~hoosier23

[~s.o.s~]

Try out something like:

#ifndef SAVINGSACCOUNT1_H
#define SAVINGSACCOUNT1_H

class SavingsAccount 
{
private:
    float annualInterestRate;
    float savingsBalance;
    
public:
    SavingsAccount()
    {
      annualInterestRate = 0;
      savingsBalance= 0;
    }
    
    SavingsAccount (float my_interest_rate, float my_savings_balance)
    {
        annualInterestRate = my_interest_rate ;
        savingsBalance = my_savings_balance ; 
    }
    
    float calculateMonthlyInterest()
    {
        float subtotal = 0;
        float monthlyint = 0;
        subtotal = savingsBalance * annualInterestRate;
        monthlyint = subtotal / 12;
        savingsBalance = monthlyint + savingsBalance;
        return savingsBalance;
    }
    
    void setInterestRate (float my_interest_rate)
    {
        annualInterestRate = my_interest_rate ;
    }
    void printSavingsBalance()
    {
        cout << "Your balance is: $" << savingsBalance << endl;
    }
};
#endif

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

int main()
{
    SavingsAccount saver1 (1, 2) ;        //instantiate saver1;
    SavingsAccount saver2 (2, 3) ;        //instantiate saver2;

    saver1.printSavingsBalance();
    cout << "Interest of Month #1" << saver1.calculateMonthlyInterest() << endl;
    saver1.setInterestRate (4);
    cout << "Interest of Month #2" << saver1.calculateMonthlyInterest() << endl;
    return 0;
}

Hope it helped, bye.

[GloriousEremite]

What is the logic behind using

float SavingsAccount::annualInterestRate = 0;
right before my main? I see that you are setting annualInterestRate to zero, but why does this need to be done? Afterall, I have made annualInterestRate .03 in the default constructor.

I believe static variables will be automatically initialized to zero or with their default constructor (and someone correct me if I'm wrong) if you don't specify, so it shouldn't be necessary. It's still often better to be explicit, though.

And don't assume that annualInterestRate will have a value of 0.3 whenever you choose to use it (if it's static, that is, since it can be used before the class constructor is called)

[Salem]

> Afterall, I have made annualInterestRate .03 in the default constructor.
You made it static, so there is only ever ONE instance of it.

You could change the assignment I posted to make it read .03 and remove the assignment from your constructor and it should still do the same thing.