problem with file upload

hi, i have a situation where i need to upload 3 img file within an array that is within another array. 2 di-array i have no problem with only variable type and value but its not working with type="file". here's my code <? for ($i=0 ; $i < 4 ; $i++) { //do something for ($k=0 ; $k < 3 ; $k++) { print "<input type=\"checkbox\" name=\"checkans[$i][$k]\" value=\"".$K."\" >"; //this is working print "<input type=\"file\" name=\"ans[$i][$k]\" >"; //this is not } } ?> i can get check[x][x] value; but i cant get ans[x][x] file; how do i do this??? thanks john