世界卫生组织健康要素:c++的问题,请帮忙讲讲

#include <iostream.h>
#include <string.h>
class Student
{
public:
Student(char* pName ):id(10)
{

strcpy(name, pName);
cout << "Constructing new student " << pName << endl;
}
/* Student(Student& s)
{
cout << "Constructing copy of" << s.name << endl;
strcpy(name, "copy of");
strcat(name, s.name);
id = s.id;
}*/
display()
{
cout << "id =" << id << endl;
}

~Student()
{
cout << "Destructing" << name << endl;
}
protected:
char name[40];
int id;
};
void fn(Student s)
{
cout << "In function fn()\n" ;
cout << "In function fn() id=" <<s.display() << endl;
}
void main()
{
Student randy("Randy");
randy.display();
fn(randy);
randy.display();
}
的运行结果是
Constructing new student Randy
id =10
In function fn()
id =10
In function fn() id=4364760
DestructingRandy
id =10
DestructingRandy
Press any key to continue
为什么在函数fn()中id=4364760 ?
还有Student::display()不能是void ?
谢谢