How to create pairs of array elements so that they match a given condition?

Question

Mathematics

Task: write a program that receives a set (array) with n>30 elements as input and sets a relation on it with given properties (reflexivity, symmetry, transitivity).
The number of pairs of elements of the initial set that belong to the relation must be at least n^3/2.
Here you can understand the relationship properties: I


have the code, but I do not know how to select pairs of elements that match the condition:

#include <iostream>
using namespace std;

int main()
{
  int a, b, c; // parameters for input
  const int size = 40; // suppose: size = 40 (40>30)
  int ARR[size];

  for (int i = 0; i < size; i++)
  {
    cin >> ARR[i];
  }

  cout << "\nChoose the properties of the relation: " << endl;
  cout << "1 - reflective" << endl
    << "2 - not reflective" << endl
    << "3 - symmetric" << endl
    << "4 - not symmetric" << endl
    << "5 - transitive" << endl
    << "6 - not transitive" << endl;
  cin >> a >> b >> c;

  cout << "Let's suppose that the operation is '>=' ";

  if (a == 1 && b == 3 && c == 5) // reflective, symmetric, transitive
  {
    for (int i = 0; i < size - 1; i++)
    {
      if (ARR[i] == ARR[i] && ARR[i] >= ARR[i + 1] >= ARR[i] && ARR[i] >= ARR[i + 1] >= ARR[i + 2])
      {
        
      }
      
    }
  }

}

The output should be in the form (a, b) - all possible pairs of elements that match the condition.
Help me sort this out, please.