std::unordered_map

#include <iostream>
#include <string>
#include <unordered_map>
 
int main()
{
 // Create an unordered_map of three strings (that map to strings)
 std::unordered_map<std::string, std::string > u =
 {
 {"RED", "#FF0000"},
 {"GREEN", "#00FF00"},
 {"BLUE", "#0000FF"}
 };
 
 // Helper lambda function to print key-value pairs
 auto print_key_value = [](const auto& key, const auto& value)
 {
 std::cout << "Key:[" << key << "] Value:[" << value << "]\n";
 };
 
 std::cout << "Iterate and print key-value pairs of unordered_map, being\n"
 "explicit with their types:\n";
 for (const std::pair <const std::string, std::string >& n : u)
 print_key_value(n.first, n.second);
 
 std::cout << "\nIterate and print key-value pairs using C++17 structured binding:\n";
 for (const auto& [key, value] : u)
 print_key_value(key, value);
 
 // Add two new entries to the unordered_map
 u["BLACK"] = "#000000";
 u["WHITE"] = "#FFFFFF";
 
 std::cout << "\nOutput values by key:\n"
 "The HEX of color RED is:[" << u["RED"] << "]\n"
 "The HEX of color BLACK is:[" << u["BLACK"] << "]\n\n";
 
 std::cout << "Use operator[] with non-existent key to insert a new key-value pair:\n";
 print_key_value("new_key", u["new_key"]);
 
 std::cout << "\nIterate and print key-value pairs, using `auto`;\n"
 "new_key is now one of the keys in the map:\n";
 for (const auto& n : u)
 print_key_value(n.first, n.second);
}

Iterate and print key-value pairs of unordered_map, being
explicit with their types:
Key:[BLUE] Value:[#0000FF]
Key:[GREEN] Value:[#00FF00]
Key:[RED] Value:[#FF0000]
 
Iterate and print key-value pairs using C++17 structured binding:
Key:[BLUE] Value:[#0000FF]
Key:[GREEN] Value:[#00FF00]
Key:[RED] Value:[#FF0000]
 
Output values by key:
The HEX of color RED is:[#FF0000]
The HEX of color BLACK is:[#000000]
 
Use operator[] with non-existent key to insert a new key-value pair:
Key:[new_key] Value:[]
 
Iterate and print key-value pairs, using `auto`;
new_key is now one of the keys in the map:
Key:[new_key] Value:[]
Key:[WHITE] Value:[#FFFFFF]
Key:[BLACK] Value:[#000000]
Key:[BLUE] Value:[#0000FF]
Key:[GREEN] Value:[#00FF00]
Key:[RED] Value:[#FF0000]