CPP Program for implementing queue as a linked list

#include<iostream.h>
#include<conio.h>

struct Node
{
int info;
 Node *next;
};

Node *front=NULL,*rear=NULL,*tmp;

void Insert()
{
tmp=new Node;
 if(tmp==NULL)
 {
  cout<<"\n Overflow";
  return;
 }
 cout<<"\n Enter information"<<endl;
 cin>>tmp->info;
tmp->next=NULL;
 if(rear==NULL)
 front=rear=tmp;
 else
 {
  rear->next=tmp;
  rear=tmp;
 }
}

void Delete()
{
tmp=front;
 if(tmp==NULL)
 {
  cout<<"\n Underflow";
  return;
 }
 cout<<"\n Information to be deleted is  "<<tmp->info;
 if(front==rear)
 front=rear=NULL;
 else
 front=front->next;
 delete tmp;
}

void Show()
{
tmp=front;
 if(tmp==NULL)
 {
  cout<<"\n Underflow";
  return;
 }
 cout<<"\n Queue is"<<endl;
 while(tmp!=NULL)
 {
 cout<<tmp->info<<" ";
tmp=tmp->next;
 }
}

void main()
{
int ch;
 do
 {
clrscr();
  cout<<"\n 1. INSERT";
  cout<<"\n 2. DELETE";
  cout<<"\n 3. SHOW";
  cout<<"\n 4. EXIT";
  cout<<endl;
  cout<<"\n Enter a choice from 1 to 4"<<endl;
  cin>>ch;

  switch(ch)
  {
   case 1:Insert();
	  break;
   case 2:Delete();
	  break;
   case 3:Show();
	  break;
   case 4:cout<<"Bye!!!";
	  break;
default:cout<<"\n Enter a choice from 1 to 4 only";
  }
getch();
 }
 while(ch!=4);
}