//menu driven program by linked list implementation of queue
#include<iostream.h>
#include<conio.h>
#include<process.h>
struct node
{ int info;
  node *next;
}*front,*rear,*np,*ptr,*temp;
void insert_Q(int INF)
{ ptr=new node;
  ptr->info=INF;
  ptr->next=NULL;
  if(ptr==NULL)
exit(1);
  if(front==NULL)
front=rear=ptr;
  else
  {  rear->next=ptr;
  rear=ptr;
  }
}
void delete_Q()
{  if(front==NULL)
  cout<<"\n Underflow";
else
{ temp=front;
  front=front->next;
}
delete temp;
}
void display(node *np)
{  clrscr();
   cout<<"\t\t";
while(np!=NULL)
{ cout<<np->info<<"-->";
  np=np->next;
}
cout<<"NULL";
}
void main()
{ clrscr();
  front=rear=NULL;
  int p,inf;
  l:
  cout<<"\n Press 1 for PUSHING"
<<"\n Press 2 for POPING"
<<"\n Press 3 for TRAVERSAL"
<<"\n Press 4 to EXIT\n";
  cout<<"\n Enter your choice:";
  cin>>p;
  if(p==4)
  { cout<<"\n THANK YOU";
exit(0);
  }
  else if(p==1)
  { cout<<"\n Enter the element to be inserted:";
cin>>inf;
insert_Q(inf);
goto l;
  }
  else if(p==2)
  { delete_Q();
goto l;
  }
  else
  { display(front);
goto l;
  }
  getch();
}