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=0; i < NUM_POINTS; i++)
    {
    xvals[i] = i/fs;
    yvals[i] = sin(2*M_PI*f0*xvals[i]);
    }
    for (i=0; i < NUM_POINTS; i++)
    {
    fprintf(temp, "%lf %lf \n", xvals[i], yvals[i]); //Write the data to a temporary file
    }

    for (i=0; i < NUM_COMMANDS; i++)
    {
    fprintf(gnuplotPipe, "%s \n", commandsForGnuplot[i]); //Send commands to gnuplot one by one.
    }
    return 0;
}