📝 Lesson 4.3: Putting It All Together

What We're Building

A Task Manager that runs in the console. When you start it, you'll see a menu:

===== TASK MANAGER =====
1. Add a task
2. List tasks
3. Mark a task complete
4. Quit
Choose an option: 1
Enter a task: Finish the C# course

Task added!

Take a moment to appreciate this: a few lessons ago, "Hello, World!" was the whole program. Now you're going to build something genuinely useful — and every piece of it uses skills you already have.

Planning the Program

Good programmers plan before they type. Let's break the app into pieces and note which lesson each draws on:

The overall flow is a classic menu-driven loop:

Step 1: The Task Class

Each task has a title and whether it's done. That's a perfect fit for a small class with two properties and a constructor:

class Task
{
    public string Title { get; set; }
    public bool IsDone { get; set; }

    public Task(string title)
    {
        Title = title;
        IsDone = false;   // new tasks start incomplete
    }
}

Notice the constructor takes only the title — a brand-new task is always incomplete, so we set IsDone = false ourselves.

Step 2: The Menu Loop

The heart of the app is a loop that shows the menu, reads a choice, and acts on it — over and over until the user picks Quit. We'll use a bool flag to control the loop:

List<Task> tasks = new List<Task>();
bool running = true;

while (running)
{
    Console.WriteLine("\n===== TASK MANAGER =====");
    Console.WriteLine("1. Add a task");
    Console.WriteLine("2. List tasks");
    Console.WriteLine("3. Mark a task complete");
    Console.WriteLine("4. Quit");
    Console.Write("Choose an option: ");

    string input = Console.ReadLine();

    switch (input)
    {
        case "1":
            // add a task
            break;
        case "2":
            // list tasks
            break;
        case "3":
            // complete a task
            break;
        case "4":
            running = false;   // ends the loop
            Console.WriteLine("Goodbye!");
            break;
        default:
            Console.WriteLine("Please choose 1-4.");
            break;
    }
}

Step 3: The Actions

Rather than cram all the logic into the switch, we'll put each action in its own method — exactly the organization Lesson 3.3 taught. Each method takes the task list and does one job.

Add a task

void AddTask(List<Task> tasks)
{
    Console.Write("Enter a task: ");
    string title = Console.ReadLine();
    tasks.Add(new Task(title));
    Console.WriteLine("Task added!");
}

List tasks

void ListTasks(List<Task> tasks)
{
    if (tasks.Count == 0)
    {
        Console.WriteLine("No tasks yet.");
        return;                       // exit early — nothing to show
    }

    for (int i = 0; i < tasks.Count; i++)
    {
        string mark = tasks[i].IsDone ? "[x]" : "[ ]";   // ternary from 3.1
        Console.WriteLine($"{i + 1}. {mark} {tasks[i].Title}");
    }
}

Complete a task

void CompleteTask(List<Task> tasks)
{
    ListTasks(tasks);
    Console.Write("Enter the task number to complete: ");

    if (int.TryParse(Console.ReadLine(), out int number))
    {
        int index = number - 1;                    // menu is 1-based, list is 0-based
        if (index >= 0 && index < tasks.Count)
        {
            tasks[index].IsDone = true;
            Console.WriteLine("Marked complete!");
        }
        else
        {
            Console.WriteLine("That task number doesn't exist.");
        }
    }
    else
    {
        Console.WriteLine("Please enter a valid number.");
    }
}

The Complete Program

Here's everything assembled into one file. Create a project (dotnet new console -o TaskManager), paste this into Program.cs, and run it with dotnet run:

List<Task> tasks = new List<Task>();
bool running = true;

while (running)
{
    Console.WriteLine("\n===== TASK MANAGER =====");
    Console.WriteLine("1. Add a task");
    Console.WriteLine("2. List tasks");
    Console.WriteLine("3. Mark a task complete");
    Console.WriteLine("4. Quit");
    Console.Write("Choose an option: ");

    string input = Console.ReadLine();

    switch (input)
    {
        case "1":
            AddTask(tasks);
            break;
        case "2":
            ListTasks(tasks);
            break;
        case "3":
            CompleteTask(tasks);
            break;
        case "4":
            running = false;
            Console.WriteLine("Goodbye!");
            break;
        default:
            Console.WriteLine("Please choose 1-4.");
            break;
    }
}

// ---- Action methods ----

void AddTask(List<Task> tasks)
{
    Console.Write("Enter a task: ");
    string title = Console.ReadLine();
    tasks.Add(new Task(title));
    Console.WriteLine("Task added!");
}

void ListTasks(List<Task> tasks)
{
    if (tasks.Count == 0)
    {
        Console.WriteLine("No tasks yet.");
        return;
    }

    for (int i = 0; i < tasks.Count; i++)
    {
        string mark = tasks[i].IsDone ? "[x]" : "[ ]";
        Console.WriteLine($"{i + 1}. {mark} {tasks[i].Title}");
    }
}

void CompleteTask(List<Task> tasks)
{
    ListTasks(tasks);
    Console.Write("Enter the task number to complete: ");

    if (int.TryParse(Console.ReadLine(), out int number))
    {
        int index = number - 1;
        if (index >= 0 && index < tasks.Count)
        {
            tasks[index].IsDone = true;
            Console.WriteLine("Marked complete!");
        }
        else
        {
            Console.WriteLine("That task number doesn't exist.");
        }
    }
    else
    {
        Console.WriteLine("Please enter a valid number.");
    }
}

// ---- The Task class ----

class Task
{
    public string Title { get; set; }
    public bool IsDone { get; set; }

    public Task(string title)
    {
        Title = title;
        IsDone = false;
    }
}

===== TASK MANAGER =====
1. Add a task
2. List tasks
3. Mark a task complete
4. Quit
Choose an option: 1
Enter a task: Finish the C# course
Task added!

===== TASK MANAGER =====
Choose an option: 1
Enter a task: Celebrate
Task added!

===== TASK MANAGER =====
Choose an option: 3
1. [ ] Finish the C# course
2. [ ] Celebrate
Enter the task number to complete: 1
Marked complete!

===== TASK MANAGER =====
Choose an option: 2
1. [x] Finish the C# course
2. [ ] Celebrate
Choose an option: 4
Goodbye!

Make It Your Own

The best way to cement your skills is to extend this program. Pick one or more challenges below — each uses concepts you already know.

void DeleteTask(List<Task> tasks)
{
    ListTasks(tasks);
    Console.Write("Enter the task number to delete: ");
    if (int.TryParse(Console.ReadLine(), out int number))
    {
        int index = number - 1;
        if (index >= 0 && index < tasks.Count)
        {
            tasks.RemoveAt(index);
            Console.WriteLine("Task deleted!");
        }
        else
        {
            Console.WriteLine("That task number doesn't exist.");
        }
    }
}

int done = 0;
foreach (Task t in tasks)
{
    if (t.IsDone)
    {
        done++;
    }
}
Console.WriteLine($"{done} of {tasks.Count} complete.");

Summary & What's Next

🚀 What's Next?

You've completed the four core modules of Introduction to C# — a huge accomplishment. But there's one more essential piece of object-oriented programming that turns good code into flexible, professional designs. In Module 5: Deeper Object-Oriented Programming, you'll learn inheritance, interfaces, and polymorphism. First up: Lesson 5.1: Inheritance.