Main.cc: In function ‘int main()’:
Main.cc:8:5: error: ‘cout’ was not declared in this scope
cout << numbers::pi
^~~~
Main.cc:8:5: note: suggested alternative: ‘cosl’
cout << numbers::pi
^~~~
cosl
Main.cc:8:13: error: ‘numbers’ has not been declared
cout << numbers::pi
^~~~~~~