初心者はどのようにC++で1つの時間のクラスを書きます

初心者はどのようにC++で1つの時間のクラスを書きます
プログラミング環境はVS 2019プロセスは簡単です.メンバー関数を定義すれば次のようになります.

#include
using namespace std;
class Time          //       
{
private :
 int hour, minute, second;
public:
 Time(int a=0 ,int b=0,int c=0);
 void settime();
 void show();
 void add();
 void reduce();
};
Time::Time(int a,int b,int c)
{
 if (a < 0 || a>24 || b < 0 || b>59 || c < 0 || c>59)
 {
  cout << "wrong time" << endl;
 }
 else
 {
  hour = a; minute = b;second = c;
 }
}
void Time::settime()
{
 int a, b, c;
 cout << "   / / " << endl;
 cin >> a >> b >> c;
 if (a < 0 || a>24 || b < 0 || b>59 || c < 0 || c>59)
 {
  cout << "wrong time" << endl;
 }
 else
 {
  hour = a; minute = b;second = c;
  cout << "     " << endl;
 }
}
void Time::show()
{
 cout << "Hour---     " << hour << "     Minute---     " << minute << "     Second---     " << second << endl;
 cout << "     " << endl;
}
void Time::add()
{
 int n,x=0;
 cout << "         :"<<endl;
 cin >> n;
 x = 3600 * hour + 60 * minute + second+n;
 hour = x / 3600;
 minute = (x % 3600) / 60;
 second = x % 60;
 cout << "done" << endl;
 cout << "     " << endl;
}
void Time::reduce()
{
 int n, x=0;
 cout << "         :" << endl;
 cin >> n;
 x = 3600 * hour + 60 * minute + second - n;   //     ，     
 hour = x / 3600;
 minute = (x % 3600) / 60;
 second = x % 60;
 cout << "done" << endl;
 cout << "     " << endl;
}
int main()                //   
{
 Time time;
 cout << "  :" << endl;
 cout << "-------    -------1" << endl;
 cout << "-------    -------2" << endl;
 cout << "-------    -------3" << endl;
 cout << "-------    -------4" << endl;
 cout << "-------    -------0" << endl;
 int m;        // do while              
 do {
  cin >> m;
  switch (m)
  {
  case 1:
  {time.settime();
  break;}
  case 2:
  {time.add();
  break;}
  case 3:
  {time.reduce();
  break;}
  case 4:
  {time.show();
  break;}
  case 0:
  {
   cout << "    " << endl;
   return 0;}
  default:
  {cout << "wrong num" << endl;}
  }
 } while (m);
 return 0;
}