/* 2次元ランダムウォーク */

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define MAX_STEPS 10000
#define PI 3.1415926 

main()
{
  unsigned int seed;
  int i,j;
  int nstep;
  float a1;
  float x[MAX_STEPS],y[MAX_STEPS];
  float xp, yp;
  float h;
  double theta;
  FILE *fp;

  printf("Input: seed\n");
  scanf("%u", &seed);
  printf("Input: Number of steps:\n");
  scanf("%u", &nstep);

  srand(seed);

  fp = fopen("2D.dat", "w");

  h=1.0;

  xp=0.0;
  yp=0.0;
  x[0]=xp;
  y[0]=yp;
  fprintf(fp, "%.5f   %.5f\n", x[0], y[0]);    

  for(i=0; i < nstep; i++){
    j=rand();
    a1=j/(RAND_MAX+1.0);
    
    theta=2*PI*a1;
    xp=xp+h * cos(theta);
    yp=yp+h * sin(theta);

    x[i+1]=xp;
    y[i+1]=yp;
    
    printf("x=%.5f,y=%.5f\n", x[i+1], y[i+1]);    
    fprintf(fp, "%.5f   %.5f\n", x[i+1], y[i+1]);   
    
  }

  return;
}