In my opinion, the best way to learn to program is to get a book at the library or buy one somewhere. What you are trying to do with this program is simple math. Take the number of questions that are incorrect and divide by the total number of questions and then multiply by 100. It's been a long time since I've done any programming, so I'm not too sure.
float total;
float incorrect;
float score;
float multiplier = 100;
score = (incorrect / total) * multiplier;
cout <<"percent correct: " score;
Like I said, it's been like 6 months since I've even touched a c++ compiler, so maybe why06 can explain it better.