void display1()
              {
        cout<<"nnnn Enter choice(123)"<<endl;
        cin>>number_1;

switch (number_1)
{
case 1:display2();
       display1();
       break;
case 2:display0();
       break;
case 3:cout<<"Exiting.............nn"<<endl;
    exit(1);
    break;
default:cout<<"You entered a wrong choice exiting.............nn"<<endl;
    exit(1);
    break;
}

void display2()
         {
                             just some cout stuff......
}


       void display3()
       {

cout<<"nnnn Enter choice(123)"<<endl;
cin>>number_2;

switch (number_2)
{

case 1:display4();
       display3();
       break;
case 2:display0();
       break;
case 3:cout<<"Exiting.............nn"<<endl;
    exit(1);
    break;
default:cout<<"You entered a wrong choice exiting.............nn"<<endl;
    exit(1);
    break;
}

int display4()
     {
 cout<<"nnnn Enter the atomic number whose details you want to see or enter -1 (to exit)"<<endl;
  cin>>choice;
  switch(choice)
          {
              some random cases........
              default : cout<< "!!!!!!!!!! YOU ENTERED A WRONG NUMBER ERROR !!!!!!!!!!";
                        exit(1);
                        break;
          }
      }