多态的应用，麻烦高手看下

#include <iostream.h>
class base
{
protected:
char name[20];
public:
virtual void set(){};
virtual void fun(){};
virtual float get(){ return 0;}
};
class stu:public base
{   float  score;
    public:
    void  set()
    {
        cout<<"please input student name:"<<endl;
        cin>>name;
        cout<<"please input "<<name<<"   score:"<<endl;
        cin>>score;
    }
void  fun(){cout<<"student:"<<endl;cout<<name<<endl<<score<<endl;}
float get(){ return score;}
};
class tec:public base
{   int  num;
    public:
    void  set()
    {
        cout<<"please teacher  name:"<<endl;
        cin>>name;
        cout<<"please input "<<name<<"    zuoping  num:"<<endl;
        cin>>num;
    }
     void  fun(){cout<<"teacher:"<<endl;cout<<name<<endl<<num<<endl;}
  float  get(){return float(num);}
};
int main()
{
    base *p=NULL;
    stu  t[3];  
    tec  z[3];
    p=t;
    for( int i=0;i<3;i++)
    {
        (p+i)->set();
    }
    for(i=0;i<3;i++)
    { if  ((p+i)->get()>90)   
        (p+i)->fun();}
    p=z;
    for(  i=0;i<3;i++)
       (p+i)->set();
    
    for(i=0;i<3;i++)
    if  ((p+i)->get()>3)   (p+i)->fun();
    return 0;
}
这个程序可以运行，也没错误，但是，输入一次后，就报错，不知道怎么回事，麻烦高手解读下！