Debugging with Xcode is fine, but sometimes we are limited, and we have to use the debugger with a lower level. To do this, we have to know that actually Xcode is not debugging anything, it uses another program called LLDB.
Note
Old versions of Xcode are used to debug with GDB instead of LLDB; don't try to use them with Swift because there is no support for Swift on GDB.
It's recommended that you know the LLDB commands if you want to debug big programs. These are also used in cases where you have to connect with another machine (a continuous integration, for example), where you have to do everything through an SSH shell.
Open the checkerboard program and check whether you have any breakpoint and remove all of them.
