for ($s;
      ^^
      useless
[download]

Fix:

    my $s = 0;
    for (; $s<=$s_no; $s++)
[download]

Better fix:

    for (my $s=0; $s<=$s_no; $s++)
[download]

Even better fix:

    for my $s (0..$s_no)
[download]