#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <math.h>
#include <g2.h>
#include <g2_X11.h>
#define PI 3.1415926
/* gcc g2_MC.c -L/usr/X11R6/lib -lm -lg2 -lX11 */
/* simple monte carlo integration  trubasic style */
int color,blk,count;
long n,N;
float x,y,pie;
int d;  /* a g2-object file handle */
int main(int argc, char*argv[])
{
    N=atol(argv[1]);
    srand((unsigned int)getpid());
    count=0;
  
    /* open a 400 by 400 pixel window */
    /* lower left is (0,0), upper right is (400,400) */
    d=g2_open_X11(400, 400);
    color=g2_ink(d,1.0,0.0,0.0); /* red */
    g2_pen(d,color);
    /* draw a bounding box */
    g2_rectangle(d,0,0,400,400);
    /* draw in some coordinate axes */
    g2_line(d, 200,0, 200, 400); /* y axis */
    g2_line(d, 0, 200, 400, 200); /* x axis */
    /* draw tick-marks */
    for(n=1; n<20;n++){
	g2_line(d,20*n,196,20*n,204);
	g2_line(d,196,20*n,204,20*n);
    }
    g2_circle(d,200.0,200.0,200.0);
    blk=g2_ink(d,0.0,0.0,0.0);
    g2_pen(d,blk);  /* black */
    for(n=0;n<N;n++){
	x=(2.0*(float)rand()/(float)(RAND_MAX)-1.0);
	y=(2.0*(float)rand()/(float)(RAND_MAX)-1.0);
	if(x*x+y*y<=1.0) count=count+1;
	g2_plot(d,200.0*x+200.0,200.0*y+200.0);  /* draw pixels */
    }
    pie=4.0*count/(float)N;
    printf("PI = %f\n", pie);
    
    /* wait until a character is entered, then exit */
    getchar();
    g2_close(d);
    return 0;
}