dict.Keys / Values / foreach

using System.Collections.Generic;

Dictionary<TKey, TValue> dict = new Dictionary<TKey, TValue>();

// Retrieves all keys.
ICollection<TKey> keys = dict.Keys;

// Retrieves all values.
ICollection<TValue> values = dict.Values;

// Iterates over key-value pairs with foreach.
foreach (KeyValuePair<TKey, TValue> pair in dict)
{
    // Access the key with pair.Key and the value with pair.Value.
}

using System;
using System.Collections.Generic;

// Creates a dictionary of countries and their capitals.
Dictionary<string, string> capitals = new Dictionary<string, string>
{
    { "Japan",   "Tokyo" },
    { "France",  "Paris" },
    { "Germany", "Berlin" }
};

// Uses Keys to iterate over the list of countries.
Console.WriteLine("--- Countries ---");
foreach (string country in capitals.Keys)
{
    Console.WriteLine(country);
}

// Uses Values to iterate over the list of capitals.
Console.WriteLine("--- Capitals ---");
foreach (string city in capitals.Values)
{
    Console.WriteLine(city);
}

// Uses KeyValuePair to access both the key and value at once.
Console.WriteLine("--- Countries and Capitals ---");
foreach (KeyValuePair<string, string> pair in capitals)
{
    Console.WriteLine($"The capital of {pair.Key} is {pair.Value}.");
}

// From C# 7.0 onward, you can use tuple deconstruction for brevity.
Console.WriteLine("--- Tuple Deconstruction ---");
foreach ((string countryName, string cityName) in capitals)
{
    Console.WriteLine($"{countryName} → {cityName}");
}

The collections returned by Keys and Values are live views of the dictionary. Any changes to the dictionary are reflected in a collection you already obtained. Adding or removing entries while iterating with foreach throws an InvalidOperationException. If you need to modify the dictionary during a loop, take a snapshot first by calling ToList().

Enumeration order may vary depending on the .NET runtime. If you need insertion-order guarantees, consider using SortedDictionary<TKey, TValue> (available from C# 8.0 onward). For adding and removing entries, see dict.Add() / Remove() / Clear(). For safe value retrieval, see dict.TryGetValue() / ContainsKey().