Turn typed text into a valid task title

Should a task containing only spaces be added to the planner? Separate missing input, blank input and a useful title before you use the text.

Predict with the supplied input

Run this complete program and enter two spaces, Read C#, then two spaces before pressing Enter. In this example, the input line is Read C# . The typed characters are input; they are not extra lines printed by the program.

using System;

Console.WriteLine("Task title:");
string? raw = Console.ReadLine();

if (string.IsNullOrWhiteSpace(raw))
{
    Console.WriteLine("Enter a title.");
}
else
{
    string title = raw.Trim();
    Console.WriteLine($"Saved: [{title}]");
}

Draw the validation gate

ReadLine
   │
   ├── null, empty, or only whitespace ──> ask for a title
   │
   └── contains text ──> Trim outer whitespace ──> use cleaned title

string? means the variable may hold a string or null. Null means no string value is present. An empty string has a value, but contains zero characters. Pressing Enter on a blank line gives an empty string; reaching the end of the input stream can give null. The program should handle both.

string.IsNullOrWhiteSpace checks for null, an empty string, or a string containing only whitespace. It gives a bool result, so it fits naturally inside if. The accepted branch runs only when some non-whitespace text exists. After that check, the compiler also understands that raw is not null in the else branch.

For this task, reject blank input first, then clean it. Do not call a method such as Trim on a possibly null string and hope that a user always types something.

Cleaning returns another value

Strings do not change their character contents in place. Keep the result of Trim if you want the cleaned text. The brackets below make otherwise invisible outer spaces visible.

using System;

string original = "  Read C#  ";
string cleaned = original.Trim();

Console.WriteLine($"[{original}]");
Console.WriteLine($"[{cleaned}]");

Try it independently

Add a rule: the cleaned title must contain at least three characters. Count after trimming, so surrounding spaces cannot satisfy the rule. Length is the number of UTF-16 code units in a string; for the simple English titles here, it matches the character count you see. More complex text can need different handling.

Test C# : expect the short-title message. Test Read : expect Saved: [Read]. Compare only after your attempt.

using System;

Console.WriteLine("Task title:");
string? raw = Console.ReadLine();

if (string.IsNullOrWhiteSpace(raw))
{
    Console.WriteLine("Enter a title.");
}
else
{
    string title = raw.Trim();
    if (title.Length < 3)
    {
        Console.WriteLine("Use at least 3 characters.");
    }
    else
    {
        Console.WriteLine($"Saved: [{title}]");
    }
}

Explain back

Explain the difference between null, empty text and spaces. Point to the line that prevents a null value from reaching Trim. Finally explain why the minimum-length rule uses the cleaned value.

References: Microsoft — Console.ReadLine and IsNullOrWhiteSpace.