Estimating the value of Pi using Monte Carlo

/*
We need to estimate the value of pi.
Area of cirle of radius r is : pi*r^2     ie. -1 to 1 on the x axis and -1 to 1 on y axis
Area of square of the same size : (2*r)^2=4r^2  ie. -1 to 1 on x-axis and -1 to 1 on y axis
so,(Area of cirle of radius r /Area of square of same size) == (pi/4)  == (number of points in circle/number of points in square)
We know the equation of circle at origin of radius 1 is: x^2 + y^2 = 1^2=1
so if our -1<=x<=1 && -1<=y<=1 then that point will definitely come inside the square but can go outside the circle also.
so,if we find 10000 points and find that how many is in cirle and how many is in square ie. pi/4
so,multiple the above value with 4 and return the value of pi.
*/

#include <bits/stdc++.h>
#define INTERVAL 10000
using namespace std;
int main(){
    int interval, i;
    double rand_x, rand_y, origin_dist, pi;
    int circle_points = 0, square_points = 0;
    srand(time(NULL));  //It will generate different set of random numbers at every program execution not rand() execution.
    for (i = 0; i < (INTERVAL * INTERVAL); i++) {
        rand_x = double(rand() % (INTERVAL + 1)) / INTERVAL;        // Randomly generated x and y values
        rand_y = double(rand() % (INTERVAL + 1)) / INTERVAL;
        origin_dist = rand_x * rand_x + rand_y * rand_y;   // Distance between (x, y) from the origin

        if (origin_dist <= 1)       // Checking if (x, y) lies inside the define circle with R=1
            circle_points++;

        square_points++;   // Total number of points generated

        pi = double(4 * circle_points) / square_points;  // estimated pi after this iteration
    }
    cout << "\nFinal Estimation of Pi = " << pi;   // Final Estimated Value
    return 0;
}