程序代码：

#include<iostream>
using namespace std;
class Student
{
public:
  Sudent(int n,int a,float s):num(n),age(a),score(s){}
  void total();
  static float average();
private:
  int num;
  int age;
  float score;
  static float sum;
  static float count;
};
void Student::total()
{
  sum+=score;
  count++;
}
float Student::average()
{return(sum/count);}
float Student::sum=0;
float Student::count=0;
int main()
{Student stud[3]={
  Student(1001,18,70),
  Student(1002,19,78),
  Student(1005,20,98)
};
  int n;
  cout<<"please input the number of students:"<<endl;
  cin>>n;
  for(int i=0;i<n;i++)
    stud[i].total();
  cout<<"the average score of"<<n<<"students is"<<Student::average()<<endl;
  return 0;
}