When ever I create a new program in Xcode(c family language) the main file created works perfectly fine in compiling the code and running it but when I create a new c++ file in the same program then Xcode just shows a duplicate error while compiling it(the code is fine, I checked it). After this the main file also shows a similar error. What to do? I am a beginner.

How to download and use GCC compiler with Xcode(CatalinaOS)? I am a beginner.