gunplot demo

 //author : Leon yangli0534@gmail.com

 #include <stdlib.h>
 #include <stdio.h>
 #include <math.h>
 #define NUM_POINTS 500
 #define NUM_COMMANDS 2

 int main()
 {
     char * commandsForGnuplot[] = {"set title \"gunplot demo\"", "plot 'data.temp'"};
     double fs = 1000000.0;
     double f0 = 10000.0;
     double xvals[NUM_POINTS] = {1.0, 2.0, 3.0, 4.0, 5.0};
     double yvals[NUM_POINTS] = {5.0 ,3.0, 1.0, 3.0, 5.0};
     FILE * temp = fopen("data.temp", "w");
     /*Opens an interface that one can use to send commands as if they were typing into the
      *     gnuplot command line.  "The -persistent" keeps the plot open even after your
      *     C program terminates.
      */
     FILE * gnuplotPipe = popen ("gnuplot -persistent", "w");
     int i;
     for (i=; i < NUM_POINTS; i++)
     {
     xvals[i] = i/fs;
     yvals[i] = sin(*M_PI*f0*xvals[i]);
     }
     for (i=; i < NUM_POINTS; i++)
     {
     fprintf(temp, "%lf %lf \n", xvals[i], yvals[i]); //Write the data to a temporary file
     }

     for (i=; i < NUM_COMMANDS; i++)
     {
     fprintf(gnuplotPipe, "%s \n", commandsForGnuplot[i]); //Send commands to gnuplot one by one.
     }
     return ;
 }