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Activity 3.3 Lists

Introduction

Lists are a convenient data type for storing elements in a collection. While they are similar to arrays in that they can store elements of a given type in a collection, there is one significant difference: lists are resizable. In other words, we don’t need to set their size, unlike arrays. This makes lists an attractive option when you need to store values in a group, but you don’t know ahead of time what the size needs to be, or if there is ever a final size. Consider this exmaple, do you always shop for the same number of items every time you go to the grocery store? Of course not. Sometimes you may have a cart overflowing with foods, and sometimes you have just a few items you need to pick up.

Lists are declared using different syntax than you may be used to: List<data type> nameOfList = new List<string>();. Notice the data type is surrounded by angle brackets. This is called generic syntax. It’s an intermediate level concept that you needn’t worry to much about at this point.

List<string> games = new List<string>();

This code initializes an empty list. Keep in mind that until elements are added, there are no available indexes. games[0] will cause an out of range error.

List.Add() Method

When you create a new list, it’s empty. Therefore, there is no index available to insert an element. To add a new element to a list, use the method List.Add(), where List is the name of your variable.

games.Add("Sonic Adventure");
games.Add("House of the Dead");
games.Add("Marvel vs. Capcom");
games.Add("Power Stone");
List.Count Property

Similar to Array.Length, List.Count returns the number of elements contained in the list. This is helpful when iterating through list elements.

Console.WriteLine($"Number of games: {games.Count}");

for (int i = 0; i < games.Count; i++)
{
    Console.WriteLine($"- {games[i]}");
}

Number of games: 4
- Sonic Adventure
- House of the Dead
- Marvel vs. Capcom
- Power Stone

Notice that elements are still accessed using the square bracket notation. You can still access and modify elements at any valid index.

List Initialization Syntax

Lists can also be initialized with data, similar to initialization syntax with arrays.

List<int> stats = new List<string>() { 99, 72, 33, 5, 100, 67, 1776 };

// For larger datasets, you can break down data over multiple lines.
List<string> roster = List<string>()
{
    "Jim",
    "Jack",
    "Joe Bob"
};
Arrays vs. Lists

Follow this rule: if you know the number of elements needed ahead of time, you can use an array. If the number of elements will vary, use a list. In theory, you could use a list for just about any scenario over an array, but you should always consider your options.

Skills to Practice

Instructions

Setup

  1. Create a new C# console application. Name the project 3.3 Lists.
  2. Click Create.

Code

List<string> tasks = new List<string>();
bool addingTasks = true;

Console.WriteLine("--- Todo List ---");

while (addingTasks)
{
    Console.WriteLine("-Menu-");
    Console.WriteLine("1) Add a task");
    Console.WriteLine("2) Finish");
    Console.Write("-> ");
    string input = Console.ReadLine();

    if (input == "1")
    {
        Console.Write("Enter task: ");
        input = Console.ReadLine();
        tasks.Add(input);
    }
    else if (input == "2")
    {
        addingTasks = false;
    }
    else
    {
        Console.WriteLine("Invalid option. Try again.\n");
    }
}

Console.WriteLine("\nPrinting List");

for (int i = 0; i < tasks.Count; i++)
{
    Console.WriteLine($"* {tasks[i]}");
}

Debug

--- Todo List ---
-Menu-
1) Add a task
2) Finish
-> 1
Enter task: Homework
-Menu-
1) Add a task
2) Finish
-> 1
Enter task: Clean bedroom
-Menu-
1) Add a task
2) Finish
-> 1
Enter task: Cook dinner
-Menu-
1) Add a task
2) Finish
-> 2

Printing List
* Homework
* Clean bedroom
* Cook dinner

Tips, Tricks, and Reflection