a simple question on default Gateway

[aryaazimi3658]

hi!
It's a simple question that one of my friend asked me and I was Unable to answer so I decided to ask here.
Why default gateway and end IP of end user computer  must be in a same subnet? for example why Router0 and PC0 are in same subnet.

[Dan Lukes]

Well, you can communicate directly with the computers on the same subnet only. For communication with computer in another subnet, the router/gateway is required.

Clear now?

Gateway is on the same subnet by definition. What the gateway not on the same subnet is good for ? Remember - you can't communicate directly with computer not on the same subnet ...