Error(s):

976080461/source.cpp: In function ‘int main()’:
976080461/source.cpp:25:9: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result]
  freopen("test50.txt", "r", stdin);
  ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
976080461/source.cpp:27:7: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d", &T);
  ~~~~~^~~~~~~~~~
976080461/source.cpp:37:8: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&N);
   ~~~~~^~~~~~~~~
976080461/source.cpp:44:9: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
    scanf("%d",&op);
    ~~~~~^~~~~~~~~~
/tmp/ccsZ1Vi6.o: In function `main':
source.cpp:(.text.startup+0x124): undefined reference to `init()'
source.cpp:(.text.startup+0x1ce): undefined reference to `visit(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)'
source.cpp:(.text.startup+0x408): undefined reference to `deleteLink(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)'
source.cpp:(.text.startup+0x450): undefined reference to `access(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)'
source.cpp:(.text.startup+0x5b6): undefined reference to `last5[abi:cxx11]()'
collect2: error: ld returned 1 exit status