UNIX for Dummies Questions & Answers

hi friends.
i want to create new file name depends upon user input value.......the format is "txt_VVVV.txt". is it possible?
#bin/ksh
typeset -i10 i = $1
case $i in
[1-9]*)
fil = "txt_000"$i".txt"
;;
[10-99]*)
fil = "txt_00" $i ".txt"
;;
*) echo "invalid filename"
exit
;;
esac
echo $fil
above i did script.. for displaying "txt_0001.txt" for input is 1 or "txt_0010.txt" for input is 10. but it is giving error, advice me to get input like above or suggest some other logic which is similar to "%o4d" in C

Code:

read a
case ${a} in
   ?) echo 000${a};;
   ??) echo 00${a};;
   ???) echo 0${a};;
esac

thanks zaxxon it's working..... how i have to check whether that file is available in that folder or not?

Code:

[ -f "$fil" ] && echo "file exists" || echo "file does not exist"

thnks wempy