/in/foo.cc:5:1: error: 'string' does not name a type
 string rpic;
 ^~~~~~
/in/foo.cc:6:10: error: variable or field 'dfs' declared void
 void dfs(string rpic[int a][int b]){
          ^~~~~~
/in/foo.cc:6:10: error: 'string' was not declared in this scope
/in/foo.cc:6:10: note: suggested alternatives:
In file included from /usr/include/c++/6/iosfwd:39:0,
                 from /usr/include/c++/6/ios:38,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/stringfwd.h:74:33: note:   'std::__cxx11::string'
   typedef basic_string<char>    string;
                                 ^~~~~~
/usr/include/c++/6/bits/stringfwd.h:74:33: note:   'std::__cxx11::string'