c++中string应该怎样用，应输入标识符是什么意思 C++问题

class person(string n = 0,string g = 0,int a = 0) : 构造函数不能写在类定义上

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

class process
{
public:
    virtual void print() = 0;
};
class person: public process
{
private:
    string name;
    string gender;
    int age;
public:
    person(string n = "默认名",string g = "男",int a = 0) 
    {
        name = n;
        gender = g;
        age = a;
    }
    virtual void print()
    {
        cout << "姓名:" << name << "性别:" << gender << "年龄:" << age << endl;
    }
};
class student :public person
{
private:

    int id;
    int score1;
    int score2;
    int score3;
public:
    student(int i, int s1, int s2, int s3):person()
    {
        id = i;
        score1 = s1;
        score2 = s2;
        score3 = s3;
    }

    virtual void print()
    {
        cout << "学号:" << id << "语文成绩:" << score1 << "数学成绩:" << score2 << "英语成绩:" << score3 << endl;
    }

};
int main()
{
    person p("张三", "男", 20);
    student s(19060102, 100, 99, 98);
    process* pro1 = new person("张四", "男", 21);
    pro1->print();
    process* pro2 = new student(19060103, 95, 80, 70);
    pro2->print();

}

姓名:张四性别:男年龄:21 学号:19060103语文成绩:95数学成绩:80英语成绩:70