The main thing to be improved on this game with more time would be allowing the same color to appear in the code multiple times. A way to do this would be to first check if the two indices of the vectors were the same when adding to the white peg variable. This causes problems with the rest of the current implementation of Mastermind, however, and would require a large amount of effort to resolve. Of course one would also have to remove the sections that prevent having the same color twice in a guess.
Another valuable takeaway for me was using a Karnaugh Map to test the program. This allowed me to test if the program worked for given inputs. For example if I knew an entry would return one black and two whites I would try it and report the actual result in the box where one black met with two white. This kind of testing for success was very helpful, as it allows one to pinpoint the problem for example “whenever there are no white pegs, there ends up being an extra black peg” would be a problem pointed out by this method. After realizing this, a developer would then be able to resolve the problem, whereas without this method they may not have even known there was a problem.