90 рекомендаций по стилю написания программ на C++

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

class Product{
private:

    int num;
    // string name;
    // string supplier;
    // int count;
    // string date;

public:

    void input(){
        // cout<<"Product:            "; getline(cin, name);
        // cout<<"Supplier:           "; getline(cin, supplier);
        // cout<<"Date:               "; getline(cin, date);
        // cout<<"Amount:             "; cin>>count;
        cout<<"Number of delivery: "; cin>>num;
    }
    static Product getkey(){
        Product key;
        cout<<"Key: ";
        cin>>key.num;
        return key;
    }
    void print(){
        cout<<"Number of delivery: "<<num<<"\n";
        // cout<<"Product:            "<<name<<"\n";
        // cout<<"Supplier:           "<<supplier<<"\n";
        // cout<<"Amount:             "<<count<<"\n";
        // cout<<"Date:               "<<date<<"\n";
    }
    void output(ostream &stream){
        stream<<num;
    }
    friend bool operator <(Product const a, Product const b){
        return a.num < b.num;
    }

    friend bool operator ==(Product const a, Product const b){
        return a.num == b.num;
    }
};

class node
{
public:
    Product data;
    node *left,
         *right;

    void output(ostream &stream){
        if(this != NULL){
            left->output(stream);
            data.output(stream);
            stream<<" ";
            right->output(stream);
        }
    }
    node(Product var){
        data = var;
        left = right = NULL;
    }
    void remove(){
        if(this != NULL){
            left->remove();
            right->remove();
            delete left;
            delete right;
        }
    }
    ~node(){
        this->remove();
    }
    void output_sheets(){
        if(this != NULL){
            if(left == NULL && right == NULL){
                data.print();
            }else{
                left->output_sheets();
                right->output_sheets();
            }
        }
    }
};

class bintree
{
private:
    node *root;
public:
    bintree(){
        root = NULL;
    }
    bool add(){
        Product new_data;
        new_data.input();

        if(root == NULL){
            root = new node(new_data);
            return true;
        }
        node *elem = root,
                        *parent = NULL;
        bool isLeft;
        while(elem != NULL){
            if(new_data == elem->data){
                return false;
            }
            isLeft = new_data < elem->data;
            parent = elem;
            if(isLeft){// если новый элемент меньше корня
                elem = elem->left;
            }else{
                elem = elem->right;
            }
        }
        if(isLeft){
            parent->left = new node(new_data);
        }else{
            parent->right = new node(new_data);
        }
        return true;
    }

    void output(ostream &stream){
        root->output(stream);
    }
    void remove_max(){
        node *elem = root,
             *prev = NULL;
        while(elem->right != NULL){
            prev = elem;
            elem = elem->right;
        }
        if(elem == root){
            root = root->left;
        }else{
            prev->right = NULL;
        }
        delete elem;
    }

    void output_sheets(){
        root->output_sheets();
    }

    Product find(){
        Product key = Product::getkey();
        node *elem = root;
        while(elem != NULL){
            if(key == elem->data){
                return elem->data;
            }else if(key < elem->data){// если новый элемент меньше корня
                elem = elem->left;
            }else{
                elem = elem->right;
            }
        }
        return Product();
    }
};

void clear(){
    cout<<"\n";
    for(int i=0; i<30; i++) cout<<"-";
    cout<<"\n";
}
void menu(){
    clear();
    cout<<"1) Add node\n";
    cout<<"2) Find node by key\n";
    cout<<"3) Output tree\n";
    cout<<"4) Remove node with max key\n";
    cout<<"5) Output tree's sheets\n";
    cout<<"6) Output in file\n";
    cout<<"0) Quit\n";
    cout<<"Your choise: ";
}
int main()
{
    bintree tree;
    int ch;
    while(true)
    {
        menu();
        cin>>ch;
        switch(ch)
        {
            case 1:
                if(!tree.add()){
                    cout<<"Element with this key exsist";
                }else{
                    cout<<"Element succesfully added";
                }
                break;
            case 2:
                tree.find().print();
                break;
            case 3:
                tree.output(cout);
                break;
            case 4:
                tree.remove_max();
                break;
            case 5:
                tree.output_sheets();
                break;
            case 6:{
                char filename[50];
                cout<<"Filename: ";
                cin>>filename;
                ofstream filestr(filename);
                if (filestr.is_open()){
                    tree.output(filestr);
                    filestr.close();
                }else{
                    cout << "Error opening file";
                }
            }
            break;
            case 0:
                return 0;
                break;
        }
    }

}