C#: Access modifiers code errors and encapsulation.

Question

Here is the example that was given in C# course on encapsulation.

class BankAccount {
private double balance=0;
public void Deposit(double n) {
balance += n;
}
public void Withdraw(double n) {
balance -= n;
}
public double GetBalance() {
return balance;
}
}
class Program
{
static void Main(string[] args)
{
BankAccount b = new BankAccount();
b.Deposit(199);
b.Withdraw(42);
Console.WriteLine(b.GetBalance());
}

I decided to play with it and changed it like this:

class BankAccount {
public double balance=0;
public void Deposit(double n) {
balance += n;
}
public void Withdraw(double n) {
balance -= n;
}
public double GetBalance() {
return balance;
}
}
class Program
{
static void Main(string[] args)
{
BankAccount b = new BankAccount();
b.Deposit(199);
b.Withdraw(42);
balance.Deposit(100);
Console.WriteLine(b.GetBalance());
}

The error appeared, that balance does not exist in this context. Why? I thought changing the access modifier from private to public will make me able to access this variable.

Answer 1

The line

balance.Deposit(100);

Here is the problem. <balance> is not defined in Main() method, <balance> is defined as member of BankAccount class. And there, it was defined as `double` type. In Main() method you treat <balance> as if it was a BankAccount instance (calling Deposit() method).

Perhaps you meant this?

b.Deposit(100);

Answer 2

In addition, making balance public means you can access it directly without going through Deposit of Withdraw. For example: b.balance = 0; would work in your version but not in the original because it is private there. But to access balance, you need an object (b) to reference it (b.balance).