关于C#：无法声明正文，因为它被标记为抽象

cannot declare a body because it is marked abstract

嗨，我是C控制台应用程序的新成员，我正在使用抽象和重写，但是我在公共抽象double compute()的第一个方法中得到了堆栈。我得到了一个错误，它说不能声明一个主体，因为它被标记为抽象。请帮助我。谢谢您！

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abstract class Cake
{
public string _flavor, _size;
public int _quantity;

public Cake(string flavor, string size, int quantity)
{
_flavor = flavor;
_size = size;
_quantity = quantity;
}

public abstract double Compute()
{
double price;
if(_flavor =="Chocolate" && _size =="Regular")
{
price = 250.50;
}
else if (_flavor =="Chocolate" && _size =="Large")
{
price = 450.50;
}
else if (_flavor =="Strawberry" && _size =="Regular")
{
price = 300.50;
}
else
{
price = 500.75;
}
return price;
}
}

class BirthdayCake:Cake
{
public int _numOfCandles;

public BirthdayCake(string flavor, string size, int quantity, int numOfCandles):base(flavor,size,quantity)
{
_numOfCandles = numOfCandles;
}

public override double Compute()
{
return _numOfCandles * 10.00;
}
}`