#include <stdio.h>
#include <math.h>
#define NX 720

int main(void){
  FILE *data, *gp;
  char *data_file;
  int i;
  double dx, x, y;

  /*------ データファイル作成 ---------- */
  data_file="out.dat";
  data = fopen(data_file,"w");

  dx=4*M_PI/NX;
  for(i=0; i<=NX; i++){
    x=-2*M_PI+i*dx;
    y=sin(x);
    fprintf(data,"%f\t%f\n", x, y);
  }
  fclose(data);

  /*------ グラフの作成 ---------- */  
  gp = popen("gnuplot -persist","w");
  fprintf(gp, "set xrange [-6.5:6.5]\n");
  fprintf(gp, "set yrange [-1.5:1.5]\n");
  fprintf(gp, "plot \"%s\" with lines linetype 1 title \"sin\"\n",data_file);
  pclose(gp);

  return 0;
}