foo.cc: In function 'int main()':
foo.cc:6:5: error: 'cout' was not declared in this scope
     cout<<a<<' '<<b;
     ^~~~
foo.cc:6:5: note: suggested alternative:
In file included from foo.cc:2:0:
/usr/include/c++/7/iostream:61:18: note:   'std::cout'
   extern ostream cout;  /// Linked to standard output
                  ^~~~

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