Improve poor design and fix mistakes

I am working on a personal project. I am familiar with pyhton and C and now I am trying to learn C++. I want to understand it more. I have a file (myfile.cpp) and want to understand what mistakes are in it and the poor design. I want a new file (myfilefixed.cpp) which has the mistakes fixed and design corrected + commentaries with the changes done so I can understand.