View Compilation Error

0_0_29652104_19759.cpp: In function 'double dfs(int)':
0_0_29652104_19759.cpp:10:23: error: 'n' was not declared in this scope
     if (s + 1 == 1 << n) {
                       ^
0_0_29652104_19759.cpp: In function 'int main()':
0_0_29652104_19759.cpp:30:9: error: 'cout' was not declared in this scope
         cout << dfs(0) << std::endl;
         ^
0_0_29652104_19759.cpp:30:9: note: suggested alternative:
In file included from 0_0_29652104_19759.cpp:1:0:
GCC4.9.2/x86_64-w64-mingw32/include/c++/iostream:61:18: note:   'std::cout'
   extern ostream cout;  /// Linked to standard output
                  ^