无法解析的外部符号 _main??

#include <iostream>
#include <fstream>
#include <string.h>
using namespace std;
class computer
{};
class parts : virtual public computer
{
private:
    char disk[20];
    char CPU[20];
public:
   
    parts(char *p = new char[20],char *q = new char[20])
    {
        strcpy(disk , p);
        strcpy(CPU , q);
    }
    void out()
    {
        cout << disk << endl;
        cout << CPU << endl;
    }
};