Культура оформления кода: что такое enum? Где, когда и для чего уместно применять этот тип?

enum ChosenOperation { ADD = 1, SHOW, SEARCH, EXIT };
 
enum SearchingCriteria { NAME = 1, ADDRESS, PHONE, AGE };

#include <iostream>
 
int main()
{
    enum Color { RED, GREEN, BLUE };
    
    std::cout
        << "red color encoded by number:\t"
        << RED
        << "\n"
        << "green color encoded by number:\t"
        << GREEN
        << "\n"
        << "blue color encoded by number:\t"
        << BLUE
        << "\n";
}

#include <iostream>
 
int main()
{
    enum Color { RED = 7, GREEN = 13, BLUE = 666 };
 
    std::cout
        << "red color encoded by number:\t"
        << RED
        << "\n"
        << "green color encoded by number:\t"
        << GREEN
        << "\n"
        << "blue color encoded by number:\t"
        << BLUE
        << "\n";
}

// chosen operation:
const int ADD = 1;
const int SHOW = 2;
const int SEARCH = 3;
const int EXIT = 4;
 
// searching criteria:
const int NAME = 1;
const int ADDRESS = 2;
const int PHONE = 3;
const int AGE = 4;

int n;
// тут много строк кода
for (int i = 0; i < n; i++)
{
    // тут много строк кода
}

std::cout << "Enter number of entries: ";
unsigned int number_of_entries;
std::cin >> number_of_entries;
 
// тут всего
// две строки кода
 
for ( unsigned int i = 0, nth; i < number_of_entries; ++i )
{
    // тут много строк кода
}

#include <iostream>
 
int main()
{
    enum DoYouSmoke { YES = 1, NO, MAYBE, NEVER, SOMETIMES };
 
    std::cout <<
        "Do you smoke?\n\n"
        "Enter an integer:\n"
        "1 - YES\n"
        "2 - NO\n"
        "3 - MAY BE\n"
        "4 - NEVER TRIED\n"
        "5 - SOMETIMES\n\n";
    int user_answer;
    std::cin >> user_answer;
 
    if ( user_answer == YES )
        std::cout << "\nBad for your health, dude.\n";
    else if ( user_answer == NO )
        std::cout << "\nGood for you, man. Wise choice.\n";
    else if ( user_answer == MAYBE )
        std::cout << "\nMay be? OK, if you don't wanna speak I leave you alone.\n";
    else if ( user_answer == NEVER )
        std::cout << "\nGood for you, man. Wise choice.\n";
    else if ( user_answer == SOMETIMES )
        std::cout << "\nHmmm... When you're drunk, huh? ;).\n";
    else
        std::cout << "\nSmoking is not your biggest problem, huh? xD.\n";
}