Question: My code is the following, I would like a to assume iteratives values like '3' , '4' and so on. My code is like:

```
a=2
#perform some basic operation like:
b=a*2
#convert it to string
c=str(b)
p path1 u 1:($1<=0?$@c:1/0) w filledcurves y=0 

```

The solution proposed on similar topic here so far did not work.

Answer: 
You should use this syntax

```
  c=''.b

```

c will be equal to 'b'
gnuplot provides both sprintf (as in the C language routine) and a private implementation gprintf that offers formatting options beyond the normal ones provided by the C language. The full details with all supported format options are in the gnuplot documentation. A very simple use would be:

```
c = sprintf("%8.3f", b)

```

However, it makes no sense to convert the value to a string if your intent is to use it in a plot command that expects a number. There is no iteration in the pseudo-code you show so I can't guess exactly where you are headed with this but note that the operation @c to evaluate c as a macro expansion inside an iteration will always yield the content of c as it was prior to the iteration. So using the @ operator inside an iteration is almost always wrong.