Here's a refresher on some possibly useful Unix commands:

g++ filename.c -o filename  (compiles the file called filename.c and
                             creates an executable file called filename)
./filename                  (runs the program; the first two characters
                             may not be necessary)
./filename > outputfile     (runs the program, putting results in a file
                             instead of on the screen)

If you set up the output in two-column format, you can then use graphing
software to read in the file and plot the second column (y-axis) versus
first column (x-axis):

gnuplot                     (runs gnuplot, a simple graphing package)
  plot "outputfile"	    (the most basic plotting command!)

  plot [xrange=0:1000] "outputfile" with lines
                            (within gnuplot, plots the first
      two columns of outputfile, using the range from 0 to 1000 for the
      horizontal axis.  You can change the xrange, or you can let 
      gnuplot decide for itself if you omit the part in square brackets.)

  plot [0:5][0:0.5] "outputfile" with linespoints
                             (within gnuplot, plots first two columns
      of outputfile, using range 0 to 5 for horizontal axis and 0 to 0.5
      for vertical axis, with both symbols for the data points and lines 
      connecting them)

  quit                       (to get out of gnuplot)