plot - Set parameters in gnuplot using C++ source code -

i'm trying plot vectors using gnuplot c++ source code. read question how interface c++ gnuplot.

this source code:

int main() {     char * commandsforgnuplot[] = {"set title \"trajectory_arm\"","plot 'data.temp' linespoints"};     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 interface 1 can use send commands if typing      *     gnuplot command line.  "the -persistent" keeps plot open after      *     c program terminates.      */     file * gnuplotpipe = popen ("gnuplot -persistent", "w");     int i;     (i=0; < num_points; i++)     {         fprintf(temp, "%lf %lf \n", xvals[i]  , yvals[i]); //write data temporary file     }      (i=0; < num_commands; i++)     {         fprintf(gnuplotpipe, "%s \n", commandsforgnuplot[i]); //send commands gnuplot 1 one.     }     return 0; } 

the problem is:

i have new vector of 5 points(a) , want have in same plot , xvals in respect of yvals. how should modify code? in case plot , xvals 2 different colors.

this complete source code formatted in c. have added third vector a, , third instruction commandsforgnuplot ('' u 1:3 w lp) plots vector a respect xvals. notice gnuplot draws each line different colors default.

#include <stdio.h> #include <stdlib.h>  #define num_points   5    // each vector has 5 points  int main() {   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};   double avals[num_points] = {4.0 ,5.0, 3.0, 0.0, 1.0};    int i;   //write xvals, yvals, , avals temporary file                 file * temp = fopen("data.temp", "w");    for(i=0; < num_points; i++)     fprintf(temp, "%lf %lf %lf\n", xvals[i]  , yvals[i], avals[i]);    fclose(temp);   // close file if won't used anymore    // open interface gnuplot. option -p lets plot windows survive after program exits   file * gnuplotpipe = popen ("gnuplot -p", "w");    // send commands gnuplot 1 one.   fprintf(gnuplotpipe, "%s \n", "set title 'trajectory\\_arm'");      // command 0: define graph title   fprintf(gnuplotpipe, "%s \n", "plot 'data.temp' u 1:2 w lp");       // command 1: plot yvals vs xvals, , avals vs xvals    fflush(gnuplotpipe);      // plots data current commands    // obtained plot of data.temp   // now, place instruction pause program until key typed   getchar();                    // add plot current graph   fprintf(gnuplotpipe, "%s \n", "replot 'data.temp' u 1:3 w lp");    pclose(gnuplotpipe);      // close gnuplot if won't used anymore   return 0; }