Q:

Why is my reference to AccountBalance returning a 0 amount?

I'm brand new to C# and am struggling with a program I am trying to create. I hope I can ask this question to the best of my ability. Per my assignment, we are creating a Windows Form in Visual Basic that creates an account. For the purpose of my question, I have an Account class, a Savings Account class (that is derived from the Account class), I have four forms, I have a AccountForm (that is the main form which displays the account number and the account amount using a string method). I have an estimate interest form, that needs to take the current AccountBalance from the account class (or savings account class, not sure which) and take user entered rate and term (which is collected from the InterestForm) to calculate an estimated interest. Right now, my AccountBalance on my InterestForm is returning 0 and I'm not sure why. Here is my code for the InterestForm.
namespace Assignment_6_third_attempt
{
    public partial class InterestForm : Form
    {

        private SavingsAccount savingsAccount = new SavingsAccount();
        //private double accountBalance;

        public InterestForm()
        {
            InitializeComponent();
        }

        public InterestForm(double accountBalance)
        {
            accountBalance = savingsAccount.AccountBalance;
            InitializeComponent();
        }

        private void addInterestButton_Click(object sender, EventArgs e)
        {
            CalculateInterest();
            // this.Close();
        }

        public void CalculateInterest()
        {
            //A = P(1 + rt)
            double accountBalance = savingsAccount.AccountBalance;
            double interestRate = double.Parse(interestUpDown.Text);
            double term = double.Parse(termUpDown.Text);
            double estimateInterest = (accountBalance * (1 + (interestRate * term)));
            estimateTextBox.Text = estimateInterest.ToString("C");
        }

    }
}

A:

Change your InterestForm constructor to:
public InterestForm(double accountBalance) : this()
{
   savingsAccount.AccountBalance = accountBalance; 
}

