foo.cc: In function 'int main()':
foo.cc:6:2: error: 'cin' was not declared in this scope
  cin>>a;
  ^~~
foo.cc:6:2: note: suggested alternative:
In file included from foo.cc:1:0:
/usr/include/c++/7/iostream:60:18: note:   'std::cin'
   extern istream cin;  /// Linked to standard input
                  ^~~
foo.cc:7:2: error: 'cout' was not declared in this scope
  cout<<a;
  ^~~~
foo.cc:7:2: note: suggested alternative:
In file included from foo.cc:1:0:
/usr/include/c++/7/iostream:61:18: note:   'std::cout'
   extern ostream cout;  /// Linked to standard output
                  ^~~~
foo.cc:11:9: error: unable to find string literal operator 'operator""b' with 'const char [4]', 'long unsigned int' arguments
   cout<<"-->"b;
         ^~~~~~
foo.cc:16:9: error: unable to find string literal operator 'operator""b' with 'const char [4]', 'long unsigned int' arguments
   cout<<"-->"b;
         ^~~~~~
foo.cc:19:2: error: break statement not within loop or switch
  break;
  ^~~~~
foo.cc:5:10: warning: unused variable 'c' [-Wunused-variable]
  int a,b,c;
          ^

[Hydro](https://hydro.ac)提供评测服务