List in C-Sharp

List in C#

In C#, List is a generic collection type provided by the .NET framework. It belongs to the System.Collections.Generic namespace. Before dive into C# List you should think about the following:

A simple example to show the basic usage of List, including creating a list, adding elements, accessing elements by index, and iterating over all elements in the list with a foreach loop.

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        // Create a list of strings
        List<string> fruits = new List<string>();

        // Add elements to the list
        fruits.Add("Apple");
        fruits.Add("Banana");
        fruits.Add("Orange");

        // Access elements by index
        Console.WriteLine(fruits[0]);  // Output: Apple

        // Iterate over all elements in the list
        foreach (string fruit in fruits)
        {
            Console.WriteLine(fruit);
        }

        // Output:
        // Apple
        // Banana
        // Orange
    }
}

Getting the List of another List in C#

In the following example we start by creating a console application using Visual Studio 2022:

I call my console app "ListOfList":

and press the Next button:

By the time I create this console application I am using .NET 8:

and press the Create button:

I create a function named GetStatesAndCities: and inside of it I want to have a list of States with their Cities I start by specifying the type of the list, note that I want a list that can hold a list of strings, the name of the list being declared, and initializes a new instance of the object using the new keyword:

// the long form:
List<List<string>> states = new List<List<string>>();

// you can also use: 
var states = new List<List<string>>();

// a simplify form: 
List<List<string>> states = new();

// a more simplify form (with C# 12): 
List<List<string>> states = [];

Here is my function where I add the states and cities list:

static void GetStatesAndCities()
{
    List<List<string>> states = [];

    states.Add(new List<string> {
        "Florida", "Miami", "Orlando", "Tampa", "Jacksonville", "Fort Lauderdale", "Tallahassee", "Key West", "Naples", "Pensacola", "Sarasota"
    });

    states.Add(new List<string> { 
        "New York", "New York City", "Buffalo", "Rochester", "Albany", "Syracuse", "Yonkers", "White Plains", "Ithaca", "Utica", "Niagara Falls" 
    });

    states.Add(new List<string> { 
        "California", "Los Angeles", "San Francisco", "San Diego", "Sacramento", "San Jose", "Oakland", "Fresno", "Long Beach", "Anaheim", "Santa Monica" 
    });

    states.Add(new List<string> { 
        "Illinois", "Chicago", "Springfield", "Peoria", "Rockford", "Aurora", "Naperville", "Champaign", "Bloomington", "Joliet", "Evanston" 
    });

    states.Add(new List<string> { 
        "Texas", "Houston", "Dallas", "Austin", "San Antonio", "Fort Worth", "El Paso", "Arlington", "Corpus Christi", "Plano", "Lubbock" 
    });

    // iterrate through the state to what we want
    for (int i = 0; i < states.Count; i++)
    {
        // only get the States name (the 1rst item in each list)
        var state = states[i];
        Console.WriteLine(state[0]);
    }
}

When you call this fuction you should ended up with the following result:

Now I I want to access the cities for each state I can update my for loop by adding another for loop like so:

// iterrate through the state to what we want
for (int i = 0; i < states.Count; i++)
{
    // only get the States name (the 1rst item in each list)
    var state = states[i];
    Console.WriteLine(state[0]);

    // get the cities
    for (int j = 1; j < state.Count; j++)
    {
        Console.WriteLine($"    --> {state[j]}");
    }
}

Now the result should look like this:

who discovers this article may wonder if I have never heard of foreach with a smile
So I reassure you, you can have the same result with a foreach loop here is the proof:

foreach (var state in states)
{
    // Get the state name (the first item in each list)
    Console.WriteLine(state[0]);

    // Get the cities
    foreach (var city in state.Skip(1)) // Skip the first item (state name)
    {
        Console.WriteLine($"    --> {city}");
    }
}

Ouf! Hope you got the idea.

I hope you enjoyed this little reading, I promise to bring you even more tutorials, so until now, good practice and happy codding!