After removing Windows7 using GParted Partition Editor, I wonder if there is any files left that will affects Ubuntu 12.04. Is there any command in the terminal to clean all the remaining files from Windows7?
There will be no files recoverable from your old Windows installation without using forensic software tools.
If you really want to bleach a drive clean, boot a LiveCD, open a terminal.
List the available disk and partitions (to work out which device your disk is)
And then copy zeroes over the whole surface
If you have completely reformatted your drive to EXT4, then I don't think there will be any old Windows file left that should bother your Ubuntu installation.
However I'm not sure about those 1.98 GB partitions. If there is nothing on them that you need, I think it should be safe to delete them and use the space as linux swap instead.