Redefinition errors in .h files

you need include guards in your header files.

Possible problem of multiple inclusions.

Try to guard your header files with #ifndef read about it here

file list.h

#ifndef _LISTH_
#define _LISTH_

<your code>

#endif

file matrix.h

#ifndef _MATRIXH_
#define _MATRIXH_

<your code>

#endif

It will prevent you too have redefinitions if you have a loop in header inclusions.

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