Errata

The word "the" appears wrong. The 'e' in the line "benefits from seeing the same content represented in multiple ways" is covered by the background of the graphic "bullet points".

Current Copy:
Relational Operators Use > and < to compare numbers and see if a number in one variable one is bigger or smaller than another.

Suggested:
"number in one variable one is bigger or" should be "number in one variable is bigger or"

Note from the Author or Editor:
Fixed typo on page 62

Current Copy
a Click event handler to your Button control. The code-behind — tthe C# code in MainWindow.xaml.cs that’s joined to your XAML —

Suggested
change "tthe" to "the"

Note from the Author or Editor:
Fixed typo on page 124

The WPF App selection title (after choosing Create a new project) has changed again. The button now reads "WPF Application." There is nothing in parentheses after the title. The descriptor text has changed to "A project for creating a .NET Core WPF Application."

This is true for the other similar screen shots in the book. This errata would replace the previous errata.

Note from the Author or Editor:
Also fixed similar issue on pages 73 and 120

redundant semicolon in " public MainWindow(); "

Note from the Author or Editor:
Thanks for pointing this out!

In the comment it says "...it sets oneNumber to the next number..." This should be "...it sets aNumber to the next number..." There is not a variable named oneNumber.

The icons used by Visual Studio for Step Into, Step Over, and Step Out have changed, so they are different from what is shown in the images underneath the first paragraph.The new images use simpler dots and arrows.

To make sure the reader gets the exception so they can fix it, change the text: "And the XAML code that appears inside the <Grid> after the row and column definitions and before the </Grid> should look like this:"

To: "Make sure the XAML code inside the <Grid> after the row and column definitions and before </Grid> looks like this, with the Label control first, then the TextBox, then the TextBlock:"

On page 77 of the the original Print Edition or page 78 of the corrected PDF, the last line on the page says "... and the TextBox now only accepts numeric input." That's not true, alphanumeric characters are accepted. At this point, we have done nothing to the control to restrict the type of input.

Note from the Author or Editor:
Remove the text ", and the TextBox now only accepts numeric input" from page 78.

3. If the user entered a number, it sets e.Handled to true, which tells WPF to ignore the input.

If the user entered a NON-NUMERIC character, then the line is correct. If the user entered a NUMBER, e.Handled is set to false.

Note from the Author or Editor:
This line should say:

3. If the user entered a non-numeric character, it sets e.Handled to true, which tells WPF to ignore the input.

In the 4th bullet it says to "expand the Layout section" to set the IsSnapToTickEnabled property to True. This property is in the Common section, so just change "Layout" to "Common." [I found it by using the Search box method taught earlier.]

There's a typo in the second bullet in step 5 on page 123. The bullet should say:
* Use the Layout section to set the height to 300 and the width to 800.

Very minor detail, but the comment supplied for the amount parameter in the summary states "Amount of cash to give." It should say "Amount of cash to receive."

Note from the Author or Editor:
In this part of the code above the ReceiveCash declaration near the bottom of the page:

/// <param name="amount">Amount of cash to give.</param>
public void ReceiveCash(int amount)

change "Amount of cash to give." to "Amount of cash to receive."

The box next to Strength has the number 911, and the box next to Dexterity is empty. These should be changed: the box next to Strength should have the number 12, and the box next to Dexterity should have the number 15.

The text in the "Using Suffixes" section refers to actions taken in the Unity labs:

"InvokeRepeating("AddABall", 1.5F, 1)"

(specifically with respect to literals). In Unity Lab 1, however, there was no C# code involved.

Note from the Author or Editor:
In the the "Use suffixes to give your literals types" section on page 162, change the first line of text to this, making the uppercase D in 10D bold and underline:
Go back to the first loop you wrote in the "Up Close" section and change 10 to 10D:

Change the line of code under it to this, making the uppercase D in 10D bold and underline:
for (float f = 10D; float.IsFinite(f); f *= f)

In the paragraph that follows that line of code, change the first sentence to this:
Now your program won't build—you'll get an error that mentions a "literal of type double.

In the line "256 cast to a byte will have a value of 0, 25 will be converted to 1"

It should be 257 will be converted to 1

Note from the Author or Editor:
Fix the typo: change "25 will be converted to 1" to "257 will be converted to 1"

The first sentence appears to refer to the example on the top of the previous page (168; see previously entered errata). That example cast a float to an int. Would change the first sentence to correspond: "You've already seen that a float can be cast to an int."

Change "between parameter" to "between a parameter"

The second sentence lists the fields starting with "Starting4D6Roll." In the code below, this field is named "RollResult." Fix by replacing "Starting4D6Roll" with "RollResult."

Guy bob... Cash = 100,...
But the graphic states "Bob" 75 - 75 should be 100?

Note from the Author or Editor:
In the graphic at the bottom of the page, change the number under "Bob" from 75 to 100. Make corresponding changes to the two graphics on page 189.

"When the user presses 3, make the app call a method that exchanges the two references"

The solution on the following page does not use a method or function to swap the references.

This method makes a random price between 2.01 and 5.97 by converting two
random ints to decimals. --> This method makes a random price between 2.01 and 4.97 by converting two random ints to decimals.

Note from the Author or Editor:
Fix the typo by changing 5.97 to 4.97 in the box at the bottom of page 208, and also in the box at the bottom of page 720.

2nd sentence in the second paragraph starts with "It has four fields..." The MenuItem class diagram pictured on the right has six fields (Randomizer, Proteins, Condiments, Breads, Description, and Price).

As explained on the next page, the ball will rotate once every two seconds (180 * Time.deltaTime). The last part of the text balloon pointing at the 8-ball says "...a speed of two rotations per second" but should say "...a speed of one rotation per two seconds."

typo

Note from the Author or Editor:
On page 234 in the third paragraph, in the phrase "it doesn't add the extra 3 HP for flaming" change 3 to 2

Add a boldfaced note in Arial Black (style "Learner Answer") to the bottom of the page that says this (with the word "after" underlined):

Now we know what caused the bug! We won’t fix this project yet.
We’ll return to fix the project after learning more about encapsulation.

You can see an image of how this should look here: https://raw.githubusercontent.com/head-first-csharp/fourth-edition/master/Additional_material/Updated_page_236.png

After adding the constructor, the main method will throw the error. The displayed error has MachineGun class, but the actual class name is PaintballGun.

Note from the Author or Editor:
Replace the screenshot on page 259 with this image: https://raw.githubusercontent.com/head-first-csharp/fourth-edition/master/Additional_material/Corrected_error_message_pages_259_and_260.png

The last statement of the PaintballGun constructor is:
if (!loaded) Reload();
When the used enters that the paintball gun is loaded (typing "True" at the prompt, this code will result in an unloaded gun ["20 balls, 0 loaded"].
To fix, delete the ! ("not" operator) before loaded for the if conditional test:
if (loaded) Reload();
This will then "load" the gun that starts empty.

The error displayed has the wrong class name "Machinegun" instead of "PaintballGun".

A couple of lines later, the code is instantiated again using "Machine gun" instead of "PaintballGun".

Note from the Author or Editor:
Replace the screenshot on page 260 with this image: https://raw.githubusercontent.com/head-first-csharp/fourth-edition/master/Additional_material/Corrected_error_message_pages_259_and_260.png

It looks like the escape sequences were not printed in the question.
"What kind of sequence is or ?"

Perhaps it meant to represent " " and " ". Or someone directly typed /n and /t.

Note from the Author or Editor:
Fixed the clue for #7, which was missing backslashes due to a printing error:

7. What kind of sequence is \n or \r?

There's a grammatical error.
"What you're doing when..." would be answered with a noun.

I suggest "To ____ two strings, use the + operator."

The last but one bullet point mentions that "Always use a subclass reference in place of base class.". The wording should be "You can always use a subclass reference in place of base class.".

Note from the Author or Editor:
Change the bullet "Always use a subclass reference in place of base class." to "You can use a subclass reference in place of base class."

The Queen class model on page 317 doesn't include a method for AddWorker, UpdateStatusReport or WorkerStatus.
In the instructions for writing the classes on page 321, there are instructions for building all methods except for the WorkerStatus method. There is no mention of this method until you look at the answer.

Note from the Author or Editor:
On page 317, add the following sentence to the end of the annotation pointing up at the Queen class: "Queen also has private methods, which we'll talk about later."

On page 321, update the last bullet in the first section that starts "Look carefully at the status reports in the screenshot" to add the following sentence to the end:

UpdateStatusReport calls a private WorkerStatus method with a string parameter called job ("Nectar Collector") and returns a string with the number of workers doing that job ("3 Nectar Collector bees").

abstract class Canine : Animal
{
public bool BelongsToPack { get; protected set; } = false;

}
}
The book sayed it has its own abstract property, BelongsToPack, but why abstract modifier didn't appear before BelongsToPack ,Thanks

Note from the Author or Editor:
That's a great question. You don't need the 'abstract' modifier because in an abstract class, every member is automatically abstract.

We can update the annotation that points to "abstract class Canine : Animal" to say the following:

The abstract Canine class extendsAnimal. It has its own abstract property, BelongsToPack. We don't need to label it abstract because in an abstract class, every member is automatically abstract.

Change "Go ahead and an" to "Go ahead and". Also in the bottom-right note it looks like it says "Deek 2" instead of "Deck 2".

The graph diagram at the bottom of the page, the Guy objects hair colour are the wrong way round. Joe should be Gray and Bob should be Red.

Also should the graph diagram not show the HairStyle objects connected to the Guy objects, not shown in the Guy objects themselves, as they do for the outfit objects?

Change this text:
Start by adding a @code block to the end of your Index.razor file. Go to the last line and type @code {. The IDE will fill in the closing curly bracket } for you. Press Enter to add a line between the brackets, then:

To this:
You're adding code to store a pairs of animal emoji that the player will match. Make sure your cursor is at the end of the line you just added, then:

The quote in the textbox in the middle of the snippet says, "the buttons are…colored differently (that's what btn-secondary does)." I've tried using Chrome and Safari for the Mac and they both appear as a sort of grayscale and all the same color.

Not sure if this should be a technical mistake or a language change of some sort.

Note from the Author or Editor:
Change "colored differently" to "shaded differently in some browsers"

The size of the box may need to increase to accommodate the additional text.