Piping data to Gnuplot from C

I've managed to create some code which will continuously send data points from a C program to gnuplot to show evolution of a time dependent Schrodinger equation. This is the function I've made which is iterated in a loop which updates the WF[] values each time: (Both x[] and WF[] are 1d)

void gnuprint(FILE *gp, double x[], int N)

{     

 int i;     

 fprintf(gp, "plot '-' with lines\n");

 for (i=0; i<N; i++){fprintf(gp, "%g %g\n", x[i],WF[2*i+1]);   

}  




fflush(gp);
fprintf(gp, "e\n");  


} 

What I really want to do next is plot the imaginary points on the same plot which are next to the real in the array: x[i], WF[2*i+2]

If I simply just add a

fprintf(gp, "%g %g\n", x[i],WF[2*i+2]); //The imaginary values

into the loop, when 'with lines' specified, the two plots link together (plot points join up). Using dots solves this but I would like both plots to be separately linked with lines and hopefully different colours. Can someone help?

This is the form of the plot i'd like:

http://ift.tt/1FXlHCH