Ios – Linker command failed with exit code 1 error in Xcode project

It look like the class Algebra5FirstViewController is compile multiple time.

Can you make sure that the .m and .mm is only included once in your project sources in Xcode? You can also confirm this by checking in the compile log (last icon at the right, next to the breakpoints icon) and see that confirm that it is only compiled once.

Also, if this class is part of a library that you link against and you have a class with the same name, you could have the same error.

Finally, you can try a clean and rebuild, just in case the old object files are still present and there is some junk in the compiled files. Just in case...

EDIT

I also note that the second reference is made in the file for ExercisesViewController. Maybe there is something in this file. Either you #imported the Algebra5FirstViewController file instead of the .h, or the ExercisesViewController has @implementation (Algebra5FirstViewController) instead of @implementation (ExercisesViewController), or there was some junk with this file that will cleaned with a Clean an Rebuild.

If you want to remove the support for any architecture, for example, ARMv7-s in your case, use menu Project -> Build Settings -> remove the architecture from "valid architectures".

You can use this as a temporary solution until the library has been updated. You have to remove the architecture from your main project, not from the library.

Alternatively, you can set the flag for your debug configuration's "Build Active Architecture Only" to Yes. Leave the release configuration's "Build Active Architecture Only" to No, just so you'll get a reminder before releasing that you ought to upgrade any third-party libraries you're using.