繼前面兩篇Day25、Day26的初步功能跟menu，接下來要邁向物件導向的分裝大法，讓我們先來把他們一個一個分類開來變成function吧～
到時候就可以直接包進method去。

首先來做menu，menu沒有return value，因此使用void：

void menu(){
    cout << "*****MENU*******" <<endl;
    cout << "1.Show Current Price" << endl;
    cout << "2.Find Crypto info" <<  endl;
    cout << "3.Find Market Cap" <<  endl;
    cout << "4.Help" <<  endl;
    cout << "5.Exit" <<  endl;
    cout << "****************" <<  endl;
}

這樣我們就能用menu()來呼叫出上面的主頁選單，

int main(){
    menu();
}

接下來是我們的swtich case，動作區域。
首先看到整塊區域因為也沒有return value，所以一樣用void包起來就可以了。

void action(){
    int option;
    cout << "Type the service you'd like to do: " << endl;
    cin >> option;
    do{
        switch(option){
            case 1:
            {
                cout << "Enter the Crypto (1.BTC, 2.ETH, 3.USDT 4. Exit):"<<endl;
                int cname;
                cin >> cname;
                cout << "You entered: " << cname << endl;
                cryptprice(cname);
                break;
            }
            case 2:
            {
                cout <<"Enter the name of the crypto you'd like to see info with:" << endl;
                cout << "1.BTC, 2.ETH, 3.USDT 4. Exit" << endl;
                int x;
                cin >> x;
                cout << "you entered: " << x<< endl;
                cryptinfo(x);
                break;}
            case 3:
            {   cout <<"Enter the crypto you'd like to see Market Cap with:" << endl;
                cout << "1.BTC, 2.ETH, 3.USDT 4. Exit" << endl;
                int y;
                cin >> y;
                cout << "Market cap is: $" << marketcap(y) << endl;
                break;}
            case 4:
                cout <<"Enter the name of the crypto you'd like to see info with:" << endl;
                // cin >> x;
                break;
            case 5:
                cout <<"Enter the name of the crypto you'd like to see info with:" << endl;
                // cin >> x;
                break;
        }
    }while (option != 5);
    
}

這樣一來int main()只需要用兩行，就可以展示出一模一樣的資訊。

int main(){
    menu();
    action();

    return 0;
}

接下來把其他的功能，如選項一、選項二等等一一包進function。

以上分類好的function讓我們能夠在執行功能後回到選單的選項，可以在選項後加上menu()、action（)，如下所示：

void cryptprice(int c){
    if(c == 1){
        ifstream file("BTC.txt", ios::in);
        if(file.is_open()){
            string s;
            while(file >> s){
                cout << s << endl;
            }
        }else{
            cout <<"Error";
        }
        file.close();
    }else if(c == 2){
        ifstream file("ETH.txt", ios::in);
        if(file.is_open()){
            string s;
            while(file >> s){
                cout << s << endl;
            }
        }else{
            cout <<"Error";
        }
        file.close();
    }else if(c == 3){
        ifstream file("USDT.txt", ios::in);
        if(file.is_open()){
            string s;
            while(file >> s){
                cout << s << endl;
            }
        }else{
            cout <<"Error";
        }
        file.close();
    }else{ //如果都不是上面的選項
        menu();  //回到選單 顯示menu
        action();   //給用戶選擇要執行哪個選項 
     }
}

void cryptinfo(int c){
    if(c == 1){
        cout << "Total Bitcoin: 19,166,487 BTC" << endl;
        cout << "First Block(Bitcoin creation date): 2009-01-09" << endl;
    }else if(c == 2){
        cout << "Total ETH: 19,166,487 BTC" << endl;
        cout << "First Block(Bitcoin creation date): 2009-01-09" << endl;
    }else if (c == 3){
        cout << "Total USDT: 19,166,487 BTC" << endl;
        cout << "First Block(Bitcoin creation date): 2009-01-09" << endl;
    }else {
        menu();
        action();
    }
}

void marketcap(int c){
    if(c == 1){
        cout << "367,982,010,627" << endl;
     }else if(c == 2){
         cout << "163,879,592,332" << endl;
     }else if(c == 3){
        cout << "68,269,066,618" <<endl;
     }else if(c == 4) {
        menu();
        action();
    }
}

void help(int c){
    if(c == 1){
        cout << "If you endure any system problem please restart the bot and login again." <<endl;
    }else if(c == 2){
    cout <<"Telephone: 120-332-593. Email: crypto-servie@cryptobot.com Open:Mon-Fri AM9:00~PM4:30"<< endl;
    }else {
        menu();
        action();
    }
}