NicoRischkau said:
My friend also from germany would like to visit me. his stamp in his passport was good until september 15. could he come back in on october 4 or does he have to wait a certain amount of time until he can come back in
There is no specific time limit one must wait in order to go
visit Canada again. The issue here is , that he will be questioned by the CBSA officer as to why he is coming to Canada again and will have to provide satisfactory proof that he has sufficient funds and is coming only for a visit and does not intend to stay or work in Canada.
You should ask your question on the relevant thread, you will probably have more answers there: http://www.canadavisa.com/canada-immigration-discussion-board/visitors-b8.0/