or, go to the parallel location in your ''objdir'' and run make there

$ make

* Now create a patch containing the changes you just made using the so called 'unified' format (-u), with 8 lines of context. By default the diff is printed to stdout, so you should redirect it to a file:

$ cvs diff -u8p . > patch.txt

* Trade patches with someone else in the class (use http://pastebin.mozilla.org and IRC), and take turns trying to apply their patch to your tree:

$ patch -p0 < patch.txt

* Now try backing-out this same patch. To do this you can call patch with the -R or --reverse option to tell it to swap the old and new files, basically reversing the patch.

$ patch -R -p0 < patch.txt