#define N 1000000000
#include<ctime>
#include<iostream>

int main()
{
    int count =0;
    double pi;
    srand(time(NULL));
    for ( int i = 0;i < N;i++)
    {   
        double x,y;
        x=( double) rand( )/ RAND_MAX;
        y=( double) rand( )/ RAND_MAX;
        if (x*x + y * y <= 1)
        {
            count++;
        }
    }
    pi =(double) count /N*4;

    printf("Single :# of trials =%14ld , estimate of pi is %1.16f\n",N, pi);
    return 0;
}给这个代码写上注释