the next way is a little trickier but it provides good results.
1. Start with a cube, not a block this time. and stick a cylinder right in the middle and just poking out the top.
2. Select both object but remember to select the cube first. Then in object menu, scroll down to "Boolean">Knife.
4. This has given you a surface replicating the shape of the cylinder.
You can also use knife and cutaway or just delete the surface after you have finished with it, because you may need to move it around! Alas I hope these help! I slept in till 12pm today,!
Steve