A memory includes many memory regions. The memory regions have multiple multi-level cells. Each memory region includes a first bit line, a second bit line, a data buffer and a protecting unit. The first bit line is coupled to a first column of the multi-level cells. The second bit line is coupled to a second column of the multi-level cells. The data buffer is coupled to the first bit line and the second bit line and for storing data to be programmed into the multi-level cells. The protecting unit is coupled to the first bit line, the second bit line and the data buffer and is for preventing a programming error from occurring.