And what if your bug is after the nth iteration of the loop, where the exact value of n is unknown (it's a bug, after all)? How many times are you going to set the variable and run the loop n times? Whereas with print-debugging and a grep you can filter for only unexpected/unusual output, and so narrow down to the likely cause, faster. Generalizing, of course. There are definitely cases where a debugger can be more effective, as others in this thread have said. It depends on the case.