How do I write a loop in a gdb script?

Question

After adapting this answer, I wrote the following loop to simply print an array in gdb in a script called "gdb_script.gs". What am I doing wrong?

set $end=64  
while ($i<$end)
   print $i
   print volfrac($i, :, 1)
   set $i=$i+1
end

where volfrac(:,:,:) is a fortran array. I am getting the error:

 gdb_script.gs:14: Error in sourced command file:
 A syntax error in expression, near `<$end)'.

Answer 1

set $i = 0
p $i++

keep pressing Enter this is one of the easiest logic I found