C# Foundations·C# from first file to first API

Types and nullability

C# is statically typed, and nullable reference types make absence explicit.

Beginner 12 min read Lesson 6 of 300 Challenge included

What you will be able to do

Use var only when the type is obvious from the right-hand side.
Prefer string? and explicit null checks over hopeful assumptions.
Use value types for small data and classes for identity.

In plain English

A variable type tells the compiler what operations are valid. With nullable reference types enabled, string means a real string and string? means it may be null. Fixing warnings is cheaper than chasing NullReferenceException later.

Program.csC#

string title = "C# Foundations";
int minutes = 12;
decimal price = 19.99m;
bool published = true;

string? subtitle = null;
Console.WriteLine(subtitle?.Length ?? 0);
Console.WriteLine(title + " · " + minutes + " min");

Your turn

Format a nullable name

Easy

Write a method that returns a display name or "Learner" when the input is null or whitespace.

CSHARP · starter

string Display(string? name)
{
    return name;
}

Check your understanding before moving on.

Knowledge checkQuestion 1

What does string? communicate in a nullable-enabled project?

Select an answer to continue

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Next: Classes, records and object design

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