Errors in file for "Build a MIDI Synthesizer" when trying to compile/run it

I downloaded the files from the Build a MIDI Synthesizer tutorial for JUCE and edited the coding in it according to what the tutorial said. After I saved it and opened it in my IDE, I tried to compile and run it, but several errors popped up instead, and I don’t know how to fix or get rid of them, or whether I should fix the code in JUCE or in my IDE application. These are some of the errors that I am seeing in my IDE. (I’m using Xcode.)

I wasn’t able to attach all of the errors into one screenshot, so I’m sharing some of them for now.

When dealing with build errors, it’s normally best to start with the very first error, as later errors may only be appearing as a result of the first issue. It looks like you may have cropped out the first few errors in that screenshot. You can also try clicking the little arrow button next to the error to see more information.