Program for Priority Queue Insertion and Deletion in C++

#include<iostream>
#include<limits.h>
#define MAX 100
using namespace std;

// struct to hold data and priority of any item in priority queue
struct item
{
  int data;
  int priority;
};

// array of type struct item
// example rather than int array[] we have item array[]
// item is a struct that holds data and priority
item pq[MAX];

// denotes where the last item in priority queue is
// initialized to -1 since no item is in queue
int idx = -1;

bool isEmpty ()
{
  return idx == -1;
}

bool isFull ()
{
  return idx == MAX - 1;
}

// enqueue just adds item to the end of the priority queue | O(1)
void enqueue (int data, int priority)
{
  if (!isFull ())
    {
      // Increase the index
      idx++;
      // Insert the element in priority queue
      pq[idx].data = data;
      pq[idx].priority = priority;
    }
}

// returns item with highest priority
// NOTE: Low priority number means higher priority | O(N)
int peek ()
{
  int maxPriority = INT_MAX;
  int indexPos = -1;

  // Linear search for highest priority
  for (int i = 0; i <= idx; i++)
    {
      // If two items have same priority choose the one with 
      // higher data value
      if (maxPriority == pq[i].priority && indexPos > -1
	  && pq[indexPos].data < pq[i].data)
	{
	  maxPriority = pq[i].priority;
	  indexPos = i;
	}

      // note low priority number means higher priority
      // ex: Two processes P1 - 1 priority and P2 - 5 priority 
      // P1 will get executed first, thus comes out of ready queue first
      else if (maxPriority > pq[i].priority)
	{
	  maxPriority = pq[i].priority;
	  indexPos = i;
	}
    }

  // Return index of the element where
  return indexPos;
}

// This removes the element with highest priority
// from the priority queue | O(N)
void dequeue ()
{
  if (!isEmpty ())
    {
      // Get element with highest priority
      int indexPos = peek ();

      // reduce size of priority queue by first
      // shifting all elements one position left
      // from index where the highest priority item was found
      for (int i = indexPos; i < idx; i++)
	{
	  pq[i] = pq[i + 1];
	}
      // reduce size of priority queue by 1
      idx--;
    }
}

void display ()
{
  for (int i = 0; i <= idx; i++)
    {
      cout << "(" << pq[i].data << ", " << pq[i].priority << ")\n";
    }
}

// Driver Code
int main ()
{
  // To enqueue items as per priority
  enqueue (10, 1);
  enqueue (20, 3);
  enqueue (30, 4);
  enqueue (40, 5);
  enqueue (1000, 2);

  cout << "Before: " << endl;
  display ();

  // Dequeue the top element
  dequeue ();			// 10 dequeued
  dequeue ();			// 1000 dequeued 

  cout << "\nAfter: " << endl;
  display ();
  return 0;
}