Build your Study Planner: add, list and complete tasks

Can you build the planner without copying the whole answer at once? Work through three checkpoints: a menu, a task list, and a completion command.

Plan the behaviour before the code

The first version keeps tasks in memory. A learner can type a to add, l to list, d to mark a numbered task done, and q to quit. Commands are the lowercase letters shown in the menu. Blank titles and invalid task numbers are rejected. Closing this version loses its tasks; the next lesson adds saving.

read command
    │
    ├─ a ──> validate title ──> add task
    ├─ l ──> show numbered tasks
    ├─ d ──> validate number ──> mark item done
    └─ q / end of input ──> finish

After a, l or d: return to the menu

Before looking at the implementation, draw three task boxes on paper. Give each a Title and an IsDone flag. The list holds references to those objects. The displayed task numbers start at 1; the list indexes start at 0.

This version keeps the StudyTask declaration small and has no explicit constructor. C# supplies a parameterless constructor. The form new StudyTask { Title = title.Trim() } creates an object and then sets its writable Title property; the braces are an object initializer. IsDone starts false, the default bool value.

Build it in small passes

The condition while (true) keeps the menu loop running. The break statement leaves that loop when q is entered or input ends. command == null detects end of input, and || accepts either exit condition. A return inside AddTask leaves that method and returns to the menu; it does not leave the outer loop.

Create a separate console project in a new folder named StudyPlannerApp. Build one checkpoint at a time; the complete program below is a reference to compare with after an attempt.

At checkpoint 1, include only the menu and its exit branch; do not call AddTask, ShowTasks or MarkDone yet. At checkpoint 2, add the StudyTask class and the two methods before connecting a and l. At checkpoint 3, add MarkDone before connecting d. This keeps every checkpoint buildable without empty placeholder methods. Run each row’s check before adding the next command.

Try the complete session

Read the program. Before running, predict the list after entering these lines, one at a time:

a
Read C#
l
d
1
l
q

Complete Program.cs — compare after your checkpoints

This is a complete replacement for Program.cs. Keep one copy of each method; do not append it to your current program.

using System;
using System.Collections.Generic;

List<StudyTask> tasks = new List<StudyTask>();
Console.WriteLine("Study Planner");
while (true)
{
    Console.WriteLine("a=add l=list d=done q=quit");
    string? command = Console.ReadLine();
    if (command == null || command == "q")
    {
        Console.WriteLine("Goodbye.");
        break;
    }
    if (command == "a") AddTask(tasks);
    else if (command == "l") ShowTasks(tasks);
    else if (command == "d") MarkDone(tasks);
    else Console.WriteLine("Unknown command.");
}

static void AddTask(List<StudyTask> tasks)
{
    Console.WriteLine("Task title:");
    string? title = Console.ReadLine();
    if (string.IsNullOrWhiteSpace(title))
    {
        Console.WriteLine("Title required.");
        return;
    }
    tasks.Add(new StudyTask { Title = title.Trim() });
    Console.WriteLine("Added.");
}

static void ShowTasks(List<StudyTask> tasks)
{
    if (tasks.Count == 0)
    {
        Console.WriteLine("No tasks yet.");
        return;
    }
    for (int i = 0; i < tasks.Count; i++)
    {
        string status = "todo";
        if (tasks[i].IsDone) status = "done";
        Console.WriteLine($"{i + 1}. [{status}] {tasks[i].Title}");
    }
}

static void MarkDone(List<StudyTask> tasks)
{
    Console.WriteLine("Task number:");
    string? text = Console.ReadLine();
    if (!int.TryParse(text, out int number) || number < 1 || number > tasks.Count)
    {
        Console.WriteLine("Invalid task number.");
        return;
    }
    tasks[number - 1].IsDone = true;
    Console.WriteLine("Completed.");
}

class StudyTask
{
    public string Title { get; set; } = "";
    public bool IsDone { get; set; }
}

In the predicted session, the first list shows 1. [todo] Read C#; the second shows 1. [done] Read C#. The MarkDone method changes the object stored in the list. It does not remove the task.

Check the contract

Your turn: add a useful command

Add c to count completed tasks without changing any tasks. Test one todo task and one done task; the result should be 1. Use a foreach loop and increase a counter only when IsDone is true. You already know every required building block. Add the command to the menu text as well as to the decision chain.

Explain your application

Describe one complete journey from reading d to changing IsDone. Name the input validation, the conversion from number to index, the changed object and the return to the menu. Keep this first version small enough that you can explain each method.

Reference: Microsoft — List<T>.