my projiect can't build, i don't understanding this problem, I think it about system
This is result of project debugging

1>------ Build started: Project: my, Configuration: Debug Win32 ------
1>Build started 9/13/2012 11:04:08 PM.
1>InitializeBuildStatus:
1> Touching "Debug\my.unsuccessfulbuild".
1>ClCompile:
1> List.cpp
1> Generating Code...
1> Compiling...
1> Stack.cpp
1> Queue.cpp
1> Poly.cpp
1> Generating Code...
1>ManifestResourceCompile:
1> All outputs are up-to-date.
1>Poly.obj : error LNK2005: "public: __thiscall List::List(void)" (??0List@@QAE@XZ) already defined in List.obj
1>Poly.obj : error LNK2005: "public: void __thiscall List::addFirst(int)" (?addFirst@List@@QAEXH@Z) already defined in List.obj
1>Poly.obj : error LNK2005: "public: void __thiscall List::clear(void)" (?clear@List@@QAEXXZ) already defined in List.obj
1>Poly.obj : error LNK2005: "public: __thiscall List::~List(void)" (??1List@@QAE@XZ) already defined in List.obj
1>Poly.obj : error LNK2005: "public: void __thiscall List::display(void)" (?display@List@@QAEXXZ) already defined in List.obj
1>Poly.obj : error LNK2005: "public: void __thiscall List::addConstant(int)" (?addConstant@List@@QAEXH@Z) already defined in List.obj
1>Poly.obj : error LNK2005: "public: void __thiscall List::addPoly(class List *)" (?addPoly@List@@QAEXPAV1@@Z) already defined in List.obj
1>Poly.obj : error LNK2005: "public: int __thiscall List::empty(void)" (?empty@List@@QAEHXZ) already defined in List.obj
1>Poly.obj : error LNK2005: "public: void __thiscall List::removeFirst(void)" (?removeFirst@List@@QAEXXZ) already defined in List.obj
1>Poly.obj : error LNK2005: "public: void __thiscall List:rintPoly(void)" (?printPoly@List@@QAEXXZ) already defined in List.obj
1>c:\users\my\documents\visual studio 2010\Projects\my\Debug\my.exe : fatal error LNK1169: one or more multiply defined symbols found
1>
1>Build FAILED.
1>
1>Time Elapsed 00:00:02.48
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========