hi,
excel strips off leading zeros because mathmatically, they are unnecessary.
usully such "numbers" are some kind of id and are technically not numbers
because you don't really want to do mathmatical stuff with them anyway.
to keep the leading zeros, prefomat as text or preceed entry with an
apostrophe.
Either preformat the cell as TEXT or precede the entry with an apostrophe:
'01239. The apostrophe does not display in the cell.
Another possibility, if the length of all entries is to be the same, you
could use a custom number format like: 00000. Using this method the leading
zero(s) will *display* 01239 but the true underlying value of the cell will
be 1239.