Correct, 0 is different than '0'.
This is normal for level 1. It's a lot of disparate new information to assimilate. Level 2 is similar. Level 3 and on are where all the concepts start to come together and the exercises are all interrelated.
This looks to me like a project structure issue; missing #includes, incorrect additional include directories, and/or incorrect/missing files being linked as part of the project.
Are you using a provided project (similar to the one provided to your during QN C++) or creating your own project...