EXIT_SUCCESS, EXIT_FAILURE
From cppreference.com
                    
                                        
                    
                    
                                                            
                    | Defined in header  <cstdlib> | ||
| #define EXIT_SUCCESS /*implementation defined*/ | ||
| #define EXIT_FAILURE /*implementation defined*/ | ||
The EXIT_SUCCESS and EXIT_FAILURE macros expand into integral expressions that can be used as arguments to the std::exit function (and, therefore, as the values to return from the main function), and indicate program execution status.
| Constant | Explanation | 
| EXIT_SUCCESS | successful execution of a program | 
| EXIT_FAILURE | unsuccessful execution of a program | 
[edit] Notes
Both EXIT_SUCCESS and the value zero indicate successful program execution status (see std::exit), although it is not required that EXIT_SUCCESS equals zero.
[edit] See also
| C documentation for EXIT_SUCCESS, EXIT_FAILURE | 


