C++ error:conflicting declaration

Question

#include <iostream>
#include <string>
using namespace std;
class student
{
string name;
public:
student(string n):name(n)
{
cout<<"registering student "<<n<<endl;
}
};

class subject
{
int score;
string name;
public:
subject(string n,int s):name(n),score(s)
{
cout<<"subject "<<n<<endl
<<"score "<<s<<endl;
}
};

int main()
{
string n;
cin>>n;
int s;

cin>>s;

student(n);
subject(n,s);

return 0;
}
main函数里
subject 那句执行是没有问题的
但是 student 那句执行的时候就报错了
但是我把student(n)换成student("name")之类的又是可以运行的

Answer 1

我也不会，有点太难了；
#include <iostream>
using namespace std;
class beijing;
class shanghai
{
public:
shanghai(int a,int b,int c)
{
benchi=a;
baoma=b;
aodi=c;
total=benchi+baoma+aodi;
}
int get_total()
{
return total;
}
friend int count (beijing b,shanghai s);
private:
int aodi,benchi,baoma,total;

};
class beijing
{
public:
beijing(int a,int b,int c)
{
benchi=a;
baoma=b;
aodi=c;
total=benchi+baoma+aodi;
}
int get_total()
{
return total;
}
friend int count(beijing b,shanghai s);
private:
int aodi,benchi,baoma,total;

};

int count(beijing b,shanghai s)
{
return b.total+s.total;
}
int main()
{
int a,b,c,d,e,f;
cout<<"上海的车奔驰（a）宝马（b）奥迪（c）"<<endl;
cin>>a>>b>>c;
cout<<"北京的车奔驰（d）宝马（e）奥迪（f）"<<endl;
cin>>d>>e>>f;
shanghai s(a,b,c);
beijing b(d,e,f);
cout<<"the total count of shanghai is: "<<s.get_total()<<endl;
cout<<"the total count of beijing is: "<<b.get_total()<<endl;
cout<<"the total count of shanghai and beijing is: "<<count(b,s)<<endl;

}
我这也错了

Answer 2

直接调构造函数是不行滴........
student a(n);
subject b(n,s);
你得实例化对象

追问

额(⊙o⊙)…对哦。。。。太感谢了！
那为什么subject那个可以运行的？我好想也没写实例化对象