/* ------------------------------------------------------------------------- * A Monte Carlo simulation of Buffon's needle experiment.  *  * Name              : buffon.c  * Author            : Steve Park & Dave Geyer  * Language          : ANSI C * Latest Revision   : 9-11-98  * -------------------------------------------------------------------------  */#include <stdio.h>#include <math.h>#include "rng.h"#define N       10000L                     /* number of replications */#define HALF_PI (2.0 * atan(1.0))          /* 1.5707963...           */#define R       1.0                        /* length of the needle   */   double Uniform(double a, double b)      /* -------------------------------------------- * generate a Uniform random variate, use a < b  * -------------------------------------------- */{  return (a + (b - a) * Random());}  int main(void){   long   i;                                /* replication index     */  long   crosses = 0;                      /* number of crosses     */  double p;                                /* estimated probability */  double u, v;                             /* endpoints             */  double theta;                            /* angle                 */  long   seed;                             /* the initial rng seed  */     PutSeed(-1);                 /* any negative integer will do      */  GetSeed(&seed);              /* trap the value of the intial seed */  for (i = 0; i < N; i++) {                    u     = Random();                                       theta = Uniform(-HALF_PI, HALF_PI);    v     = u + R * cos(theta);    if (v > 1.0)      crosses++;  }  p = (double) crosses / N;                /* estimate the probability */  printf("\nbased on %ld replications and a needle of length %5.2f\n", N, R);  printf("with an initial seed of %ld\n", seed);  printf("the estimated probability of a cross is %5.3f\n\n", p);  return (0);}