In [1]:
cout << 1 << endl;

input_line_7:2:2: error: use of undeclared identifier 'cout'; did you mean 'std::cout'?
 cout << 1 << endl;
 ^~~~
 std::cout
/opt/miniconda3/gcc/include/c++/iostream:61:18: note: 'std::cout' declared here
  extern ostream cout;          /// Linked to standard output
                 ^
input_line_7:2:15: error: use of undeclared identifier 'endl'; did you mean 'std::endl'?
 cout << 1 << endl;
              ^~~~
              std::endl
/opt/miniconda3/gcc/include/c++/ostream:590:5: note: 'std::endl' declared here
    endl(basic_ostream<_CharT, _Traits>& __os)
    ^
In [2]:
using namespace std;
In [3]:
cout << 1 << endl;

input_line_9:2:15: error: reference to overloaded function could not be resolved; did you mean to call it?
 cout << 1 << endl;
              ^~~~
/opt/miniconda3/gcc/include/c++/ostream:590:5: note: possible target for call
    endl(basic_ostream<_CharT, _Traits>& __os)
    ^
/opt/miniconda3/gcc/include/c++/ostream:245:7: note: candidate function not viable: no overload of 'endl' matching 'const void *' for 1st argument
      operator<<(const void* __p)
      ^
/opt/miniconda3/gcc/include/c++/system_error:209:5: note: candidate function [with _CharT = char, _Traits = std::char_traits<char>] not viable: no overload of 'endl' matching 'const std::error_code' for 2nd argument
    operator<<(basic_ostream<_CharT, _Traits>& __os, const error_code& __e)
    ^
/opt/miniconda3/gcc/include/c++/ostream:117:7: note: candidate function not viable: no overload of 'endl' matching '__ios_type &(*)(__ios_type &)' (aka 'basic_ios<char, std::char_traits<char> > &(*)(basic_ios<char, std::char_traits<char> > &)') for 1st argument
      operator<<(__ios_type& (*__pf)(__ios_type&))
      ^
/opt/miniconda3/gcc/include/c++/ostream:127:7: note: candidate function not viable: no overload of 'endl' matching 'std::ios_base &(*)(std::ios_base &)' for 1st argument
      operator<<(ios_base& (*__pf) (ios_base&))
      ^
/opt/miniconda3/gcc/include/c++/ostream:166:7: note: candidate function not viable: no overload of 'endl' matching 'long' for 1st argument
      operator<<(long __n)
      ^
/opt/miniconda3/gcc/include/c++/ostream:170:7: note: candidate function not viable: no overload of 'endl' matching 'unsigned long' for 1st argument
      operator<<(unsigned long __n)
      ^
/opt/miniconda3/gcc/include/c++/ostream:174:7: note: candidate function not viable: no overload of 'endl' matching 'bool' for 1st argument
      operator<<(bool __n)
      ^
/opt/miniconda3/gcc/include/c++/ostream:178:7: note: candidate function not viable: no overload of 'endl' matching 'short' for 1st argument
      operator<<(short __n);
      ^
/opt/miniconda3/gcc/include/c++/ostream:181:7: note: candidate function not viable: no overload of 'endl' matching 'unsigned short' for 1st argument
      operator<<(unsigned short __n)
      ^
/opt/miniconda3/gcc/include/c++/ostream:189:7: note: candidate function not viable: no overload of 'endl' matching 'int' for 1st argument
      operator<<(int __n);
      ^
/opt/miniconda3/gcc/include/c++/ostream:192:7: note: candidate function not viable: no overload of 'endl' matching 'unsigned int' for 1st argument
      operator<<(unsigned int __n)
      ^
/opt/miniconda3/gcc/include/c++/ostream:201:7: note: candidate function not viable: no overload of 'endl' matching 'long long' for 1st argument
      operator<<(long long __n)
      ^
/opt/miniconda3/gcc/include/c++/ostream:205:7: note: candidate function not viable: no overload of 'endl' matching 'unsigned long long' for 1st argument
      operator<<(unsigned long long __n)
      ^
/opt/miniconda3/gcc/include/c++/ostream:220:7: note: candidate function not viable: no overload of 'endl' matching 'double' for 1st argument
      operator<<(double __f)
      ^
/opt/miniconda3/gcc/include/c++/ostream:224:7: note: candidate function not viable: no overload of 'endl' matching 'float' for 1st argument
      operator<<(float __f)
      ^
/opt/miniconda3/gcc/include/c++/ostream:232:7: note: candidate function not viable: no overload of 'endl' matching 'long double' for 1st argument
      operator<<(long double __f)
      ^
/opt/miniconda3/gcc/include/c++/ostream:270:7: note: candidate function not
In [ ]: