View Compilation Error

0_0_23897316_30821.cpp: In function 'void work()':
0_0_23897316_30821.cpp:145:13: error: invalid conversion from 'int' to 'void*' [-fpermissive]
   free(ST->n); 
             ^
In file included from GCC4.9.2/x86_64-w64-mingw32/include/c++/cstdlib:72:0,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/ext/string_conversions.h:41,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/basic_string.h:2850,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/string:52,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/locale_classes.h:40,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/ios_base.h:41,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/ios:42,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/ostream:38,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/iostream:39,
                 from 0_0_23897316_30821.cpp:3:
GCC4.9.2/x86_64-w64-mingw32/include/stdlib.h:438:16: note: initializing argument 1 of 'void free(void*)'
   void __cdecl free(void *_Memory);
                ^