If you plan to Hike the Half Dome without cables then you need some hiking equipment do to so.
It's recommended that you do use the cables to Hike the Half Dome because it allows you to climb up 400 feet easier than it would be without it.
Still using the cables it's pretty difficult hiking the Half Dome which is around a 14 to 16 mile round trip and you should be in pretty great physical shape to make the hike even with the cables.
You'll also need a permit to hike the half dome and rangers do check so you will be caught if you try and hike the half dome without a permit and could face 6 months in jail or a $5,000.00 fine.