Stack in linked list

There are 3 errors in my program, what do they mean??Thanks

error LNK2001: unresolved external symbol _pop
error LNK2001: unresolved external symbol _push
Debug/CheckBrackets.exe : fatal error LNK1120: 2 unresolved externals

It means your linker can't find the specified functions to link with. Oh and post some code.

prototype is available but defination is not.......