I'm going to page @Rick19744 for this but a couple of things to note:
If the conversion happens during the tax year, the corporation must file two separate tax returns for that year, one for the S corporation (1120-S) and another for the C corporation (1120).
You should be aware that you will not be able to elect S corporation status thereafter without approval from the IRS for five years.
If the corporation is an S corporation at the end of the year, then the items of income, recognized loss, gain, etc. will be passed through to the then current shareholders on their K-1s.
