Gnu Plot - ';' expected - error - loops

Question

I have a set of *.txt files, called test0001.txt, test0002.txt, .....
I want to convert the data of these files to *.png images (Out0001.png, ...).
set xrange [0:50]
set yrange [0:50]
set size square
set nokey
set pointsize 0.5
set terminal png size 1024,1024
do for [t=1:50] {
outfile = sprintf('Out%04.0f.png',t)
set output outfile
plot ('test%04.0f.txt',t) using 1:2 with points pt 7 lc rgb "black"
}
I get "';' expected in line 12" as error. Just typing in the *.txt file names works btw:
plot 'test0001.txt' using 1:2 with points pt 7 lc rgb "black"
This just creates the first image 50 times.

Answer 1

The first thing I'd be looking at was this line:
plot ('test%04.0f.txt',t) using 1:2 with points pt 7 lc rgb "black"
Since an earlier line used sprintf to do this string formatting, shouldn't you be looking at something like:
plot sprintf('test%04.0f.txt',t) using 1:2 with points pt 7 lc rgb "black"
Or, in toto, something like:
set xrange [0:50]
set yrange [0:50]
set size square
set nokey
set pointsize 0.5
set terminal png size 1024,1024
do for [t=1:50] {
inpfile = sprintf('Out%04.0f.txt',t)
outfile = sprintf('Out%04.0f.png',t)
set output outfile
plot inpfile using 1:2 with points pt 7 lc rgb "black"
}