It depends on the type of account you have. If you
Post# of 30028
If you don't have a margin account you can buy shares in the morning sell them later in the day and then re-buy them before the close. The shares from the final buy can't be resold for three days. You can do so but you do run the risk that trading in your account could be suspended for 90 days. However the first few times your broker may give you a pass.
I've done it several times in a non margin account and received an e-mail warning.
Better to ask a customer service rep at your brokerage what their policy is.