foo.cpp:23:19: error: 'void Solve::solve()' should have been declared inside 'Solve'
 void Solve::solve()
                   ^
foo.cpp: In function 'int main()':
foo.cpp:164:15: error: 'fin' was not declared in this scope
  Solve::solve(fin, fout);
               ^
foo.cpp:164:20: error: 'fout' was not declared in this scope
  Solve::solve(fin, fout);
                    ^