运行 ID: 20755

Main.cc:2:11: error: expected identifier before ‘using’
 namespace using std;
           ^~~~~
Main.cc:2:17: error: expected nested-name-specifier before ‘std’
 namespace using std;
                 ^~~
Main.cc: In function ‘int main()’:
Main.cc:6:5: error: ‘cin’ was not declared in this scope
     cin>>a>>b;
     ^~~
Main.cc:6:5: note: suggested alternative:
In file included from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:75:0,
                 from Main.cc:1:
/usr/include/c++/7/iostream:60:18: note:   ‘std::cin’
   extern istream cin;  /// Linked to standard input
                  ^~~