How do I convert an integer to a string in gnuplot?

Are you looking for something like:

plot for [c=1:5] datafile using (column(c)):(column(c+1))

This will do: plot datafile u 1:2, "" u 2:3, "" u 3:4, "" u 4:5, "" u 5:6

You can Use intrinsic function sprintf to convert numbers to string

gnuplot>  a=3; b=6;
gnuplot>  plot a*x+b title sprintf("a=%1.2f; b=%1.2f",a,b)