It seems to me you don't really want your break to be determined by the value you're breaking on, but on it being the third number.

my @datan = qw(1 2 3 4 5 6);
for ($cnt=0; $cnt<=$#datan; $cnt++) {
 print "\n" if $cnt%3 == 0;## remainder==zero after division by 3
 print "$datan[$cnt] ";
}
print "\n";
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Using this you could arbitrarily increase the number of elements, not worry about their values, and it would always give you three elements to a row. To get them to line up, unless you're assured of using single digits, you'd probably either want to use sprintf or at least separate them by tabs.