Printing using awk

Hi
I am relatively new to awk so i am getting confused a lot
I am in need of help ... I am trying to append coloumns to the end of line using AWK

I tried using this command

awk -F "," '{for(s=7;s<=217;s++);$s="0";}1' OFS=, sam_sri_out

It is giving me an output like this...

1002,306413,R,2009,211,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,0

But I want 0's and not blank space in between Comma.

Also please tell me if there is a way if I can use variables inside the Awk By which i mean

awk -F "," '{for(s=$l;s<=217;s++);$s="0";}1' OFS=, sam_sri_out 

is not working , because it is taking the value of the $l field from the file

awk -F "," '{for(s=6;s<=NF;s++){$s="0"}}1' OFS=, sam_sri_out