title: entry point (_main) undefined. for architecture x86_6 error
body: <p>I am very new to Xcode and have been using a research as I need it method to learn. I am making an app for a final project in my AP Comp Sci class. I am wondering if anyone has an idea of where my error might be for this error message:</p>
  
  <pre>
  Ld /Users/AshleyHamilton/Library/Developer/Xcode/DerivedData/BTOS-fwvvqofheqlokcazrsdkgqhnnzjg/Build/Products/Debug-iphonesimulator/BTOS.app/BTOS normal x86_64 (in target: BTOS)
  
  cd /Users/AshleyHamilton/Desktop/BTOS
  
  export IPHONEOS_DEPLOYMENT_TARGET=12.2
  
  /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -arch x86_64 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator12.2.sdk -L/Users/AshleyHamilton/Library/Developer/Xcode/DerivedData/BTOS-fwvvqofheqlokcazrsdkgqhnnzjg/Build/Products/Debug-iphonesimulator -F/Users/AshleyHamilton/Library/Developer/Xcode/DerivedData/BTOS-fwvvqofheqlokcazrsdkgqhnnzjg/Build/Products/Debug-iphonesimulator -filelist /Users/AshleyHamilton/Library/Developer/Xcode/DerivedData/BTOS-fwvvqofheqlokcazrsdkgqhnnzjg/Build/Intermediates.noindex/BTOS.build/Debug-iphonesimulator/BTOS.build/Objects-normal/x86_64/BTOS.LinkFileList -Xlinker -rpath -Xlinker /usr/lib/swift -Xlinker -rpath -Xlinker @executable_path/Frameworks -mios-simulator-version-min=12.2 -dead_strip -Xlinker -object_path_lto -Xlinker /Users/AshleyHamilton/Library/Developer/Xcode/DerivedData/BTOS-fwvvqofheqlokcazrsdkgqhnnzjg/Build/Intermediates.noindex/BTOS.build/Debug-iphonesimulator/BTOS.build/Objects-normal/x86_64/BTOS_lto.o -Xlinker -export_dynamic -Xlinker -no_deduplicate -Xlinker -objc_abi_version -Xlinker 2 -fobjc-link-runtime -L/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/iphonesimulator -Xlinker -add_ast_path -Xlinker /Users/AshleyHamilton/Library/Developer/Xcode/DerivedData/BTOS-fwvvqofheqlokcazrsdkgqhnnzjg/Build/Intermediates.noindex/BTOS.build/Debug-iphonesimulator/BTOS.build/Objects-normal/x86_64/BTOS.swiftmodule -Xlinker -sectcreate -Xlinker __TEXT -Xlinker __entitlements -Xlinker /Users/AshleyHamilton/Library/Developer/Xcode/DerivedData/BTOS-fwvvqofheqlokcazrsdkgqhnnzjg/Build/Intermediates.noindex/BTOS.build/Debug-iphonesimulator/BTOS.build/BTOS.app-Simulated.xcent -Xlinker -dependency_info -Xlinker /Users/AshleyHamilton/Library/Developer/Xcode/DerivedData/BTOS-fwvvqofheqlokcazrsdkgqhnnzjg/Build/Intermediates.noindex/BTOS.build/Debug-iphonesimulator/BTOS.build/Objects-normal/x86_64/BTOS_dependency_info.dat -o /Users/AshleyHamilton/Library/Developer/Xcode/DerivedData/BTOS-fwvvqofheqlokcazrsdkgqhnnzjg/Build/Products/Debug-iphonesimulator/BTOS.app/BTOS
  
  ld: entry point (_main) undefined. for architecture x86_64
  
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  </pre>
  
  <p>I am very frustrated and tried many methods that I found on several different sites.</p>