Priority Queue implementation using Array in C++

#include<iostream>
#define N 20
using namespace std;
int Q[N], Pr[N];
int r = -1, f = -1;
void enqueue (int data, int p)	//Enqueue function to insert data and its priority in queue
{
  int i;
  if ((f == 0) && (r == N - 1))	//Check if Queue is full
    cout << "Queue is full";
  else
    {
      if (f == -1)		//if Queue is empty
	{
	  f = r = 0;
	  Q[r] = data;
	  Pr[r] = p;

	}
      else if (r == N - 1)	//if there there is some elemets in Queue
	{
	  for (i = f; i <= r; i++)
	    {
	      Q[i - f] = Q[i];
	      Pr[i - f] = Pr[i];
	      r = r - f;
	      f = 0;
	      for (i = r; i > f; i--)
		{
		  if (p > Pr[i])
		    {
		      Q[i + 1] = Q[i];
		      Pr[i + 1] = Pr[i];
		    }
		  else
		    break;
		  Q[i + 1] = data;
		  Pr[i + 1] = p;
		  r++;
		}
	    }
	}
      else
	{
	  for (i = r; i >= f; i--)
	    {
	      if (p > Pr[i])
		{
		  Q[i + 1] = Q[i];
		  Pr[i + 1] = Pr[i];
		}
	      else
		break;
	    }
	  Q[i + 1] = data;
	  Pr[i + 1] = p;
	  r++;
	}
    }

}

void display ()			//print the data of Queue
{
  int i;
  for (i = f; i <= r; i++)
    {
      cout << "Element =" << Q[i] << " Priority = " << Pr[i] << endl;
    }
}

void dequeue ()			//remove the data from front
{
  if (f == -1)
    {
      cout << "Queue is Empty";
    }
  else
    {
      cout << "deleted Element =" << Q[f] << endl;
      cout << "Its Priority = " << Pr[f] << endl;
      if (f == r)
	f = r = -1;
      else
	f++;
    }
}

int main ()
{
  int opt, n, i, data, p;
  cout << "Enter Your Choice:-" << endl;
  do
    {
      cout <<
	"1 for Insert the Data in Queue\n2 for show the Data in Queue \n3 for Delete the data from the Queue\n0 for Exit"
	<< endl;
      cin >> opt;
      switch (opt)
	{
	case 1:
	  cout << "Enter the number of data" << endl;
	  cin >> n;
	  cout << "Enter your data and Priority of data" << endl;
	  i = 0;
	  while (i < n)
	    {
	      cin >> data;
	      cin >> p;
	      enqueue (data, p);
	      i++;
	    }
	  break;
	case 2:
	  display ();
	  break;
	case 3:
	  dequeue ();
	  break;
	case 0:
	  break;
	default:
	  cout << "Incorrect Choice" << endl;

	}
    }
  while (opt != 0);
  return 0;
}