Static Data Member in c++

#include<iostream>
#include<conio.h>
using namespace std;
class name
{
      private:
      static int num;
      public:
             name();
             void display();
             };
           
             int name::num=0;
             name::name()
             {
                  ++num;
                  }
                  void name::display()
                  {
                     
      cout<< "number ="<< num<< endl;
    
                       }
int main()
{
name a,b,c,d,e,g,t;
a.display();
getch();
    }