c++问题哪位大神帮我看看哪里错，输不出结果

Question

#include <iostream>
using namespace std;
class student
{
public:
student(string a,int b,double c){ name=a; no=b;deg=c; sum+=deg; num++;};
~student(){};
static void avg(){ cout<<"总分为:"<<sum<<"平均成绩:"<<(sum/num)<<endl;};
void display(){ cout<<"姓名:"<<name<<"学号:"<<no<<"成绩:"<<deg<<endl;};
private:
int no;
string name;
double deg;
static double sum;
static double num;
};

int main() {
student s1("小黄",1,89);
s1.display();
student s2("小陈",2,78);
s2.display();
student s3("小花",3,94);
s3.display();
student::avg();
return 0;
}

Answer 1

你的静态成员变量都没有初始化啊。

在int main前面加上：
double student::sum = 0.0;
double student::num = 0.0;

Answer 2

没有包含头文件#include<string>
用了string变量记得要加头文件

不是静态变量初始化问题，你不初始化系统自动初始化为0