foo.cc:3:7: error: expected nested-name-specifier before 'namepace'
 using namepace std; // 命名空间 std 防止标识符名称的冲突
       ^~~~~~~~
foo.cc: In function 'int main()':
foo.cc:8:1: error: 'cout' was not declared in this scope
 cout <<"A" << end1;
 ^~~~
foo.cc:8:1: 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:8:15: error: 'end1' was not declared in this scope
 cout <<"A" << end1;
               ^~~~
foo.cc:8:15: note: suggested alternative: 'enum'
 cout <<"A" << end1;
               ^~~~
               enum

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