#include<iostream>
#include<fstream>
#include<string>
struct emp{
    int eno;
    char name[50],address[50];
    float basic,allowence,deduction;
};
void addEmp(); //adds new record to data file
void disEmp(); //displays all records from file
void delEmp(); //asks empNo and removes that record from file
void updEmp(); //asks empno and lets you reenter that data
void cls(); //just clear screen
int main(){
    string dummy;
    int choice;
    cout<<"===== Main Menu ====="<<endl;
    cout<<endl<<endl;
    cout<<"1 -> Add Record "<<endl;
    cout<<"2 -> Display Record"<<endl;
    cout<<"3 -> Delete Record"<<endl;
    cout<<"4 -> Update Record"<<endl;
    cout<<endl;
    cout<<"0 -> Exit"<<endl;
    cout<<endl<<endl<<"Selection ";
    cin>>choice;
    if(choice<0 || choice>4){
        cls();
        main();
    }
    switch(choice){
        case 0:    break;
        case 1:    addEmp();    break;
        case 2:    disEmp();    break;
        case 3:    delEmp();    break;
        case 4:    updEmp();    break;
    }
}
void addEmp(){
    fstream data;
    string dummy;
    emp e;
    int choice;
    do{
        cls();
        cout<<"===== Enter New Record ====="<<endl;
        cout<<endl<<endl;
        cout<<"Eno :\t\t"; cin>>e.eno;
        getline(cin,dummy); //just to clear input buffer
        cout<<"\nName :\t\t"; gets_s(e.name,50);
        cout<<"\nAddress :\t"; gets_s(e.address,50);
        cout<<"\nBasic Salary :\t";cin>>e.basic;
        cout<<"\nAllowence :\t";cin>>e.allowence;
        cout<<"\nDeductions :\t";cin>>e.deduction;
        cout<<endl<<endl;
        cout<<"1 -> Save  | 2 -> Cancel"<<endl;
        cin>>choice;
    }while(!(choice==1 || choice==2));
    if(choice==1){
        data.open("data.dat",ios::out|ios::app);
        data.write((char*)&e,sizeof(e));
        data.close();
        cout<<"\nRecord Saved "<<endl<<endl;
    }else{
        cout<<"\n\nRecord Cancelled"<<endl<<endl;
    }
    cout<<"Enter another record?"<<endl;
    cout<<"1 -> Yes  | 2 -> No"<<endl;
    cin>>choice;
    if(choice==1)
        addEmp();
    else
        return;
    main();
}
void disEmp(){
    fstream data;
    emp e;
    data.open("data.dat",ios::in);
    cls();
    while(data.read((char*) &e, sizeof(e))){
        cout<<"\n\n-----Displaying record for ENO " <<e.eno<<endl;
        cout<<"\nName :\t\t"<<e.name;
        cout<<"\nAddress :\t"<<e.address;
        cout<<"\nBasic Salary :\t"<<e.basic;
        cout<<"\nAllowence :\t"<<e.allowence;
        cout<<"\nDeductions :\t"<<e.deduction<<endl;
        cout<<endl<<"\nTotal Salary :\t"<<e.basic+e.allowence;
        cout<<"\nNet Paid :\t"<<e.basic+e.allowence-e.deduction;
        cout<<endl;
    }
    data.close();
    main();
}
void delEmp(){
    fstream data, temp;
    emp e;
    int eno;
    cls();
    cout<<"===== Delete Record ====="<<endl;
    cout<<endl<<endl<<endl;
    cout<<"Enter ENO to delete record ";cin>>eno;
    rename("data.dat","temp.dat");
    data.open("data.dat",ios::app);
    temp.open("temp.dat",ios::in);
    temp.seekg(0,ios::beg);
    while(temp.read((char*)&e,sizeof(e))){
        if(!(e.eno==eno)){
            cout<<"Record to delete "<<e.eno;
            data.write((char*) &e,sizeof(e));
        }
    }
    data.close();
    temp.close();
    system("Del temp.dat");
    main();
}
void updEmp(){
    fstream data, temp;
    emp e;
    string dummy;
    int eno;
    cls();
    cout<<"===== Update Record ====="<<endl;
    cout<<endl<<endl<<endl;
    cout<<"Enter ENO :_";cin>>eno;
    rename("data.dat","temp.dat");
    data.open("data.dat",ios::app);
    temp.open("temp.dat",ios::in);
    temp.seekg(0,ios::beg);
    while(temp.read((char*)&e,sizeof(e))){
        if(e.eno==eno){
            cout<<"-----Current data for ENO: "<<e.eno;
            cout<<"\nName :\t\t"<<e.name;
            cout<<"\nAddress :\t"<<e.address;
            cout<<"\nBasic Salary :\t"<<e.basic;
            cout<<"\nAllowence :\t"<<e.allowence;
            cout<<"\nDeductions :\t"<<e.deduction<<endl;
            cout<<endl<<"\nTotal Salary :\t"<<e.basic+e.allowence;
            cout<<"\nNet Paid :\t"<<e.basic+e.allowence-e.deduction;
            cout<<endl<<endl;
            cout<<"-----Enter New Values-----"<<endl;
            cout<<"\nEno :\t\t"; cin>>e.eno;
            getline(cin,dummy); //just to clear input buffer
            cout<<"\nName :\t\t"; gets_s(e.name,50);
            cout<<"\nAddress :\t"; gets_s(e.address,50);
            cout<<"\nBasic Salary :\t";cin>>e.basic;
            cout<<"\nAllowence :\t";cin>>e.allowence;
            cout<<"\nDeductions :\t";cin>>e.deduction;
        }
        data.write((char*) &e,sizeof(e));
    }
    data.close();
    temp.close();
    system("Del temp.dat");
    main();
}
void cls(){
    for (int i=0;i<50;i++)
        cout<<"\n";
}

At least must answer one. Please
Comment each and every line in this program.
Also how to convert this C++ object-oriented code in just C++ so that it could be complied on "Turbo C++ IDE" i.e. it can be able to use header files of .h extesion.
Thanks in advance. Thanks a lot.

We don't do homework or coursework for you and that looks suspiciously like coursework or a mock exam question.

The idea of YOU commenting each line is to see if YOU understand what each line of code is meant to do.

any C code can be compiled using C++,
C++ is C plus extra features (OOP, easier memory management, ..)