C#
Summary - Class constants
Combine const, readonly and enum to write a MathConstants class.
Summary - Class constants
In this group you learned C#'s immutable-value tools: const is a compile-time constant, readonly a runtime immutable, static readonly a shared runtime immutable and enum a set of named constants.
const causes versioning issues in public APIs; static readonly is preferred there. readonly suits per-instance immutable values. enum groups related constants type-safely and prevents numeric mix-ups.
Exercise Constants class (summary)
Define a static class Constants. Add a public const int MaxSize = 10; field. In Main, print Constants.MaxSize.
Show example solution
Add `static class Constants { public const int MaxSize = 10; }`. In Main write `Console.WriteLine(Constants.MaxSize);`.
Example solution:
using System;
static class Constants
{
public const int MaxSize = 10;
}
class Program
{
static void Main()
{
Console.WriteLine(Constants.MaxSize);
}
}
Exercise Configuration class (summary)
Add a public readonly string Environment; field to Configuration. The constructor should assign this.Environment = env;. In Main, create new Configuration("Test") and print Environment.
Show example solution
Add `public readonly string Environment;` to Configuration. In the ctor write `this.Environment = env;`. In Main write `var c = new Configuration("Test"); Console.WriteLine(c.Environment);`.
Example solution:
using System;
class Configuration
{
public readonly string Environment;
public Configuration(string env)
{
this.Environment = env;
}
}
class Program
{
static void Main()
{
var c = new Configuration("Test");
Console.WriteLine(c.Environment);
}
}
Next step
Class constants keep immutable values tidy and type-safe. const is fast and embedded; readonly is flexible; enum groups related options. The next group will combine these in a real Quiz app project with constant score values, readonly quiz settings and enum states.
Remember: static readonly for public APIs, const for internal constants, readonly for per-instance immutability.
Test yourself
-
Which statement about class constants is correct?
- const is assigned in a constructor.
- const is implicitly static, readonly is an instance member.
- readonly embeds the value at compile time.
- enum only holds string values.
Show answer
const is implicitly static, readonly is an instance member. — Correct. const is implicitly static; readonly is an instance member assigned in the ctor.
-
Fill in the blank: readonly in constructor
class Configuration
{
public readonly string Environment;
public Configuration(string env)
{
this.____ = env;
}
}
Show answer
class Configuration
{
public readonly string Environment;
public Configuration(string env)
{
this.Environment = env;
}
}
Next lesson: Quiz model
