c++程序运行错误求解！

想问一下这个c++程序哪里出了错误，然后应该怎么改过来，求解！

#include<iostream>
using namespace std;

class Student{
	public:
		void scoretotalcount(double s);
		static float sum();
		static float average();
	private:
		float score;
		static float total;
		static int count;
};

void Student::scoretotalcount(double s){
	score = s;
	total += s;
	count++;
}

float Student::sum(){
	return total;
}

float Student::average(){
	float av;
	av = total / count;
	return av;
}

float Student::total = 0;
int Student::count = 0;

int main(){
	Student a;
	double score;
	cout << "请输入班级成绩：(-1结束)" << endl;
	cin >> score;
	while(score != -1){
		a.scoretotalcount(score);
		cin >> score;
	}
	cout << "全班总分为:" << a.sum() << endl;
	cout << "全班平均分为:" << a.average() << endl;
	return 0;
}