Class Vs Struct (Replace struct to class )

  #include <iostream>

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

    struct ABC {

        public:
            virtual void Sum() {
            cout << "ABC Sum()" << endl;
        }
    };

    struct XYZ: public ABC {

        public:
            int a = NULL;
        void Sum() override {
            cout << "XYZ Sum()" << endl;
        }
    };



    float main() {

        //ofstream file("test.txt",ios::binary);

        //if (file.is_open()) {
        // /*file << "1";
        // file << "2";*/
        // int number = 10;
        // file.write(reinterpret_cast<char*>(&number), sizeof(number));
        // int number2 = 20;
        // file.write(reinterpret_cast<char*>(&number2), sizeof(number2));

        // file.close();
        // cout << "Success";
        //}

        ifstream file("test.txt", ios::binary);

        if (file.is_open()) {
            /*file << "1";
            file << "2";*/
            int number ;
            file.read(reinterpret_cast<char*>(&number), sizeof(number));
            int number2 ;
            file.read(reinterpret_cast<char*>(&number2), sizeof(number2));

            file.close();
       #include <iostream>
#include <fstream>
#include <string>
            using namespace std;

            struct ABC {

                public:
                    virtual void Sum() {
                    cout << "ABC Sum()" << endl;
                }
            };

            struct XYZ: public ABC {

                public:
                    int a = NULL;
                void Sum() override {
                    cout << "XYZ Sum()" << endl;
                }
            };



            float main() {

                //ofstream file("test.txt",ios::binary);

                //if (file.is_open()) {
                // /*file << "1";
                // file << "2";*/
                // int number = 10;
                // file.write(reinterpret_cast<char*>(&number), sizeof(number));
                // int number2 = 20;
                // file.write(reinterpret_cast<char*>(&number2), sizeof(number2));

                // file.close();
                // cout << "Success";
                //}

                ifstream file("test.txt", ios::binary);

                if (file.is_open()) {
                    /*file << "1";
                    file << "2";*/
                    int number ;
                    file.read(reinterpret_cast<char*>(&number), sizeof(number));
                    int number2 ;
                    file.read(reinterpret_cast<char*>(&number2), sizeof(number2));

                    file.close();
                    cout << "Success";

                    cout << "number=" << number << endl;
                    cout << "number2=" << number2 << endl;


                }

                return 0;
            }
            cout << "Success";

            cout << "number=" << number << endl;
            cout << "number2=" << number2 << endl;


        }

        return 0;
    }