foo.cc: In function 'int main()':
foo.cc:7:9: error: 'cin' was not declared in this scope
    7 |         cin>>a;
      |         ^~~
foo.cc:14:25: error: 'cout' was not declared in this scope
   14 |                         cout<<a<<b<<c<<endl;
      |                         ^~~~
foo.cc:14:40: error: 'endl' was not declared in this scope
   14 |                         cout<<a<<b<<c<<endl;
      |                                        ^~~~
foo.cc:18:25: error: 'cout' was not declared in this scope
   18 |                         cout<<a<<c<<b<<endl;
      |                         ^~~~
foo.cc:18:40: error: 'endl' was not declared in this scope
   18 |                         cout<<a<<c<<b<<endl;
      |                                        ^~~~
foo.cc:26:17: error: 'cout' was not declared in this scope
   26 |                 cout<<b<<a<<c<<endl;
      |                 ^~~~
foo.cc:26:32: error: 'endl' was not declared in this scope
   26 |                 cout<<b<<a<<c<<endl;
      |                                ^~~~
foo.cc:30:25: error: 'cout' was not declared in this scope
   30 |                         cout<<b<<c<<a<<endl;
      |                         ^~~~
foo.cc:30:40: error: 'endl' was not declared in this scope
   30 |                         cout<<b<<c<<a<<endl;
      |                                        ^~~~

[Hydro](https://hydro.ac)提供评测服务