Hello! I have a problem. When I successfully build the sim it says: (screenshot) What's happening there? Thank you!

Hello! I am a new to programming and developing and I have a question: I tried using Xcode and copied my code from Playgrounds into my Xcode Project. But now it says 50 times "Cannot find (...) in scope." In Playgrounds my code worked. What am I doing wrong? Thank you very much!