菜鸟问题，大侠进来解释一下下。

[逍遥_WX]

#include <iostream.h>
#include <stdlib.h>
class student
{
public:
float Cal_Grade(int tempGrade)
{
return tempGrade;
}
};
class graduate:public student
{
public:
float Cal_Grade(int tempGrade)
{
return 30+tempGrade*0.7;
}
};
float fn(student &x,int tempGrade)
{
return x.Cal_Grade(tempGrade);
}
int main()
{
student s;
graduate gs;
cout<<"The grade of s="<<s.Cal_Grade(80)<<endl;
cout<<"The grade of gs="<<gs.Cal_Grade(80)<<endl;
cout<<"The grade of s="<<fn(s,80)<<endl;
cout<<"The grade of gs="<<fn(gs,80)<<endl;

system("PAUSE");
return 0;
}

运行结果为:
The grade of s=80
The grade of gs=86
The grade of s=80
The grade of gs=80----------------这一个结果不懂，请大侠解释一下。

[prototype]

Cal_Grade should be virtual. if not, 'x.Cal_grade' will call 'student's member function instead of the 'graduate's.

[我不懂电脑]

结果是对的呀。
The grade of s=80 //student
The grade of gs=86 //graduate
The grade of s=80 //student
The grade of gs=80 //graduate强制转换成了student

[fayekiss]

The grade of gs=80
这句没错,传的是graduate,函数接收时,回调用student的一个复制构造函数(C++编译器自动产生)强制转换成了student.

[wlz47]

float fn(student &x,int tempGrade)
{
return x.Cal_Grade(tempGrade);
}
由参数x传来的对象调用的都将是student::Cal_Grade

[winfit]

这就是类的多态性，调用的参数虽然是graduate ，但函数的指针为student，所以调用的是它的基类，而不是graduate