纠错？解决方案

#include<iostream>
#include<cmath>
using namespace std;
class stud
{
public:
    stud(char no[],char name[],float deg)
    {
        strcpy(x1,name);
        strcpy(x2,no);
        x3=deg;
        sum=0;
        num=0;
        num++;
    }
    stud(stud &s)
    {
        strcpy(x1,s.x1);
        strcpy(x2,s.x2);
        x3=s.x3;
    }
void disp()
{
    cout<<x1<<" "<<x2<<" "<<x3<<endl;
    cout<<avg()<<endl;
}
float avg()
{
    float s;
    sum=sum+x3;
    s=sum/num;
    return s;
}
private:
    char x1[20],x2[20];
    float x3;
    float sum,num;
};

void main()
{
    char a[20]={0},b[20]={0};
    float c;
    cin>>a>>b>>c;
    stud s(a,b,c);
    s.disp();
}

------解决方案--------------------

#include <iostream>
#include <string>
using namespace std;

static int num=0;
static float sum=0;	

class Student
{
public:
	/*
	Student()
	{
		name=NULL;
		number=NULL;
		grade=0;
		num=0;
	}
	*/

	Student(string name,string number,float grade)
	{
		this->name=name;
		this->number=number;
		this->grade=grade;
		num++;
		sum+=grade;
	}


	string GetName()
	{
		return name;
	}

	string GetNumber()
	{
		return number;
	}

	float GetGrade()
	{
		return grade;	
	}

private:
	string name;
	string number;
	float grade;
};

float GetAverage()
{
	float average=0;
	average=sum/num;
	return average;	
}

int main()
{
	string name,number;
	float grade;


	int num;
	cout<<"The number of students:";
	cin>>num; 

	cout<<"Please input the information of student:"<<endl;
	for(int i=0;i<num;i++)
	{
		cout<<"student:"<<i+1<<endl;
		cout<<"Name:";
		cin>>name;
		cout<<"Number:";
		cin>>number;
		cout<<"Grade:";
		cin>>grade;
		cout<<endl;
		Student student(name,number,grade);	
	}

	cout<<endl<<"The average score is:";
	cout<<GetAverage()<<endl;

	return 0;
}

运行结果
The number of students:3
Please input the information of student:
student:1
Name:Henry
Number:01
Grade:90

student:2
Name:perter
Number:02
Grade:89

student:3
Name:Justin
Number:03
Grade:91


The average score is:90