Eric Lippert on Cargo Cult Programming
This blog posting from Eric Lippert has a ton of good advice for new programmers. It's not specific to C++, but the principles all apply:
There are lots of cargo cult programmers -- programmers who understand what the code does, but not how it does it. Therefore, they cannot make meaningful changes to the program. They tend to proceed by making random changes, testing, and changing again until they manage to come up with something that works.
Bottom line... understand the meaning and purpose of every line of code before you try to change it.