CPP Program for implementing stack as a linked list

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

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

Node *top=NULL,*tmp;

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

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

void Show()
{
tmp=top;
 if(tmp==NULL)
 {
  cout<<"\n No element to show";
  return;
 }
 cout<<"\n Stack is"<<endl;
 while(tmp!=NULL)
 {
  cout<<tmp->info<<endl;
tmp=tmp->next;
 }
}

void main()
{
int ch=1;
 while(ch!=4)
 {
clrscr();
  cout<<"\n 1. PUSH";
  cout<<"\n 2. POP";
  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:Push();
	  break;
   case 2:Pop();
	  break;
   case 3:Show();
	  break;
   case 4:cout<<"\n Bye!!!";
	  break;
default:cout<<"\n Enter a choice from 1 to 4 only";
  }
getch();
 }
}