Hrm, you could really work on your indentation, as it would help you and others to read your code. Right now, your code is basically unreadable. Try applying a few rules like these:

• Each indent is a tab, with your editor set to show 8 spaces for a tab (or 4 spaces, on languages with longer identifiers, like Java)
• Curlies for conditions, loops, or labeled blocks go on the same line as the statement it goes with.
• Curlies for subroutines are on a line by themselves.
• After a curly, each line is indented one more than the indentation of the line the curly is on until the closing curly.

You'll hear as many opinions on style as there are programmers. In particular, the first rule on the above list (about the definition of a "tab") is a big flame war issue. However, I know for sure that having some consistant style is infinatly better then no style at all.

Note that the above isn't my complete style rules, but is enough to get your code in a much more readable state.

Here's what I get when I apply the above rules to your code, getting rid of comments as I go:

my $d=scalar(@b)/3;
for (my $i=0; $i<=$#ddts; $i++) {
        for (my $index=0;$index<=($d-1);$index++) {
                my $x=(($#b-1)-$index*3);
                $new="<td><input type=\"$b[$x]\" name=\"$b[$x-1]\"></t
+d>";
                print "<table><tr><td>$ddts[$i]</td>$new</tr></table>"
+;
        }
}
[download]

Which is much nicer to read, though it could still use some improvment (like maybe breaking up a few of the print statements, or using qq// instead of regular double quotes). You may find that you don't need to use so many comments anymore, since your code will be nice enough to read that you don't need them very often.

Also note that when I was formatting the above, I found you had a missing semicolon that I bet would have been otherwise buried.

To answer your actual question, you use the '.' operator to concatnate strings. The fastest and easiest way to concatnate an array is to use join.

Yes, Perl::Tidy :)

bash$ cat unreadable
my $d=scalar(@b)/3 # @b is the array with the content of the file
for (my$i=0; $i<=$#ddts; $i++){
#@ddts is the array in which is the result of an html form
for (my $index=0;$index<=($d-1);$index++)
{my $x=(($#b-1)-$index*3);# i calculate the position of the second wor
+d from each row, there is the html type i need
$new="<td><input type=\"$b[$x]\" name=\"$b[$x-1]\"></td>";
print "<table><tr><td>$ddts[$i]</td>$new</tr></table>";
}
}

bash$ perltidy unreadable

bash$ cat unreadable.tdy
my $d = scalar(@b) / 3    # @b is the array with the content of the fi
+le
  for ( my $i = 0 ; $i <= $#ddts ; $i++ ) {

    #@ddts is the array in which is the result of an html form
    for ( my $index = 0 ; $index <= ( $d - 1 ) ; $index++ ) {
        my $x =
          ( ( $#b - 1 ) - $index * 3 )
          ; # i calculate the position of the second word from each ro
+w, there is the html type i need
        $new = "<td><input type=\"$b[$x]\" name=\"$b[$x-1]\"></td>";
        print "<table><tr><td>$ddts[$i]</td>$new</tr></table>";
    }
}

bash$
[download]

open INPUT, "input.txt" or die "Can't open input.txt: $!\n";
print '<table>';
while (<INPUT>) {
    @words=split /\s+/;
    printf "<tr><td>%s</td><td><input type=\"%s\" name=\"%s\"></td></t
+r>", $words[0], $words[1], $words[0];
}
print '</table>';
close INPUT;
[download]

Update: Put <tr></tr> in the right places.

Update 2: I tweaked HTML so that each checkbox gets more unique (but potentially not) name. :)

I try also with join but I don't understand why, if I have 2 elements in $new , the print line prints twice: one time the element o f the array @ddts + the first element of $new, and second time the same element of the array with the second element of $new. I belive that is because of the second for loop, exactly the value of $d. I want on the same line to have the element of the @ddts array and the elements of $new. Thank you very much

Can you show me what your current output is and how you want it to look?