main.cpp:28:5: error: ‘cout’ was not declared in this scope code example

Example: error: ‘cout’ was not declared in this scope

#include <iostream>
using namespace std;

adding above two lines before main will help you

NOTE:
note: suggested alternative:
In file included from class.cpp:1:0:
/usr/include/c++/7/iostream:61:18: note:   ‘std::cout’
   extern ostream cout;  /// Linked to standard output
                  ^~~~