一个sizeof的有关问题

一个sizeof的问题！
代码如下：

Animal.h文件：

#ifndefANIMAL_H
#define   ANIMAL_H
#include <string>
using   std::string;

class   Animal{
public:
virtual   void   who()   const;
virtual   string   sound()   const=0;
virtual   ~Animal();
protected:
Animal(string   n,int   w);
string   name;
int   weight;
};

class   Sheep:public   Animal{
public:
Sheep(string   n,int   w);
virtual   void   who()   const;
virtual   string   sound()   const;
private:
string   s;
};

class   Dog:public   Animal{
public:
Dog(string   n,int   w);
virtual   void   who()   const;
virtual   string   sound()   const;
private:
string   s;
};

class   Cow:public   Animal{
public:
Cow(string   n,int   w);
virtual   void   who()   const;
virtual   string   sound()   const;
private:
string   s;
};

class   Zoo{
public:
Zoo();
void   set(Animal*   a[]);
void   show(int   n)   const;
private:
Animal*   pAnimal[50];
};

#endif


Animal.cpp文件：

#include "Animal.h "
#include <iostream>
#include <string>
using   std::string;
using   std::cout;
using   std::endl;

Animal::Animal(string   n,int   w){
name=n;
weight=w;
}

void   Animal::who()   const{
cout < <name < < "的体重为： " < <weight;
}

Animal::~Animal(){}

Sheep::Sheep(string   n,int   w):Animal(n,w){
s= "mian   mian   mian ";
}

void   Sheep::who()   const{
cout < <name < < "的体重为： " < <weight;
}

string   Sheep::sound()   const{
return   s;
}

Dog::Dog(string   n,int   w):Animal(n,w){
s= "wang   wang   wang ";
}

void   Dog::who()   const{
cout < <name < < "的体重为： " < <weight;
}

string   Dog::sound()   const{
return   s;
}

Cow::Cow(string   n,int   w):Animal(n,w){
s= "wo   wo   wo ";
}

void   Cow::who()   const{
cout < <name < < "的体重为： " < <weight;
}

string   Cow::sound()   const{
return   s;
}

Zoo::Zoo(){
for(int   i=0;i <50;i++)
pAnimal[i]=0;
}

void   Zoo::set(Animal*   a[]){
for(int   i=0;i <sizeof   a/sizeof   a[0];i++){
pAnimal[i]=a[i];
}
}

void   Zoo::show(int   n)   const{
for(int   i=0;i <n;i++){
pAnimal[i]-> who();
cout < < "   叫声是： " < <pAnimal[i]-> sound() < <endl;
}
}


main.cpp文件

#include <iostream>
using   std::cout;
using   std::endl;
#include "Animal.h "

int   main(){
Animal*   b[]={new   Sheep   ( "山羊 ",200),
  new   Sheep   ( "绵羊 ",300),
  new   Dog   ( "狼狗 ",80),

  new   Dog   ( "狮子狗 ",20),
  new   Cow   ( "奶牛 ",500),
  new   Cow   ( "母牛 ",550),};
Zoo   z;
z.set(b);
z.show(sizeof   b/sizeof   b[0]);
for(int   i=0;i <sizeof   b/sizeof   b[0];i++)
delete   b[i];

return   0;
}


运行出错。原因是：sizeof   b是24，而sizeof   a是4。b作为参数传递给a，那a和b应该一样嘛，怎么a比b小呢？请各位高手指点，谢谢！！！


[解决办法]
int a,*b;
sizeof(b)==sizeof(&a)!=sizeof(*b)==sizeof(a) 应该是这样的
b 的类型是int * 不是int