“对象”不包含“名称”的定义

Question

I'm having an error message that tells me this:

'BankAccount.account' does not contain a definition for 'withdraw'.

Here's my code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace BankAccounts
{
class account
{
    protected string name;
    protected float balance;
    public account(string n, float b)
    {
        name = n;
        balance = b;
    }

    public void deposit(float amt)
    {
        balance -= amt;
    }

    public void display()
    {
        Console.WriteLine("Name: {0}. Balance: {1}.", name, balance);
    }
}

class savingaccount : account
{
    static int accno = 1000;
    int trans;
    public savingaccount(string s, float b) : base(s, b)
    {
        trans = 0;
        accno++;
    }
    public void withdraw (float amt)
    {
        if (trans >= 10)
        {
            Console.WriteLine("Number of transactions exceed 10.");
            return;
        }
        if (balance - amt < 500)
            Console.WriteLine("Below minimum balance.");
        else
        {
            base.withdraw(amt);
            trans++;
        }
    }
    public void deposit(float amt)
    {
        if (trans >= 10)
        {
            Console.WriteLine("Number of transactions exceed 10.");
            return;
        }
        base.deposit(amt);
        trans++;
    }
    public void display()
    {
        Console.WriteLine("Name: {0}. Account no.: {1}. Balance: {2}", name, accno,        balance);
    }
}

class currentaccount : account
{
    static int accno = 1000;
    public currentaccount(string s, float b) : base(s, b)
    {
        accno++;
    }
    public void withdraw(float amt)
    {
        if (balance - amt < 0)
            Console.WriteLine("No balance in account.");
        else
            balance -= amt;
    }
    public void display()
    {
        Console.WriteLine("Name: {0}. Account no.: {1}. Balance: {2}.", name, accno, balance);
    }
}

}

I don't understand why it doesn't recognize it. It is a method in the class savingaccount.

Answer 1

You're calling

base.withdraw(amt);

from your class savingsaccount . But the base class ( account ) has no such method. So the compiler is absolutely correct.

Answer 2

It looks like you simply missed the method from the base type:

public virtual void Deposit(float amt)
{
    balance += amt;
}
public virtual void Withdraw(float amt)
{
    balance -= amt;
}

Note I changed "deposit" to += , and made the method virtual so that subclasses can override the method, which is (I strongly suspect) what the intent is here. Additionally, float is a really bad choice for storing money. decimal might be a better choice. As a stylistic change, I also capitalized the names.

Answer 3

I assume your intention was to define the basic withdraw method in the base account class, so that it would be inherited by both savingaccount and currentaccount . You should declare it as virtual in order to allow it to be overridden by the derived classes, if required.

class account
{
    public virtual void withdraw(float amt)
    {
        if (balance - amt < 0)
            Console.WriteLine("No balance in account.");
        else
            balance -= amt;
    }
}

The currentaccount class presumably does not need to modify the logic of this inherited method, so you can omit it altogether. On the other hand, in your savingaccount class, you can override the method to implement your custom behaviour:

class savingaccount : account
{
    public override void withdraw(float amt)
    {
        if (trans >= 10)
        {
            Console.WriteLine("Number of transactions exceed 10.");
            return;
        }
        if (balance - amt < 500)
            Console.WriteLine("Below minimum balance.");
        else
        {
            base.withdraw(amt);
            trans++;
        }
    }
}

Answer 4

您在savingaccount类中调用base.withdraw(amt) ，但基类account未定义此方法。

Answer 5

If you look closely, you'll see that your account class in fact doesn't have a withdraw method.

I'd guess you meant to have your account class contain a virtual method withdraw , defined like this: public virtual void withdraw(float amt) { ... }

Then, in your inherited classes you'd want to override this method, like so:

class currentaccount : account
{
    public override void withdraw(float amt)
    {
        ...
        base.withdraw(amt)
        ...
    }
    ...
}

There's also a naming style issue with your code, but this is probably not in the scope of this question :)

Answer 6

正如大家已经指出的，你应该在你的基类账户上声明withdraw()方法，这样所有的派生类都可以继承该方法。