Chapter 2: Speaking C#

Question 1

non-generic types

Answer 1

System.Collections.Hashtable

Question 2

generic types

Answer 2

System.Collections.Generic.Dictionary<TKey, TValue>
List<T></T>

Question 3

Events are built on …..

Answer 3

delegates

Question 4

define delegate

Answer 4

public int MethodIWantToCall(string input)
{
return input.Length; // it doesn’t matter what the method does
}

delegate int DelegateWithMatchingSignature(string s);

// create a delegate instance that points to the method
DelegateWithMatchingSignature d = new(p1.MethodIWantToCall);
// call the delegate, who then calls the method
int answer2 = d(“Frog”);

Question 5

What statement can you type in a C# file to discover the compiler and language version?

Answer 5

error version

Question 6

How to output the SDK version?

Answer 6

dotnet –version

Question 7

Enabling a specific language version compiler

Answer 7

<LangVersion>7.3</LangVersion>

7, 7.1, 7.2, 7.3, 8, 9,
10, 11
latestmajor
latest
preview

Question 8

How to add LangVersion in .csproj file?

Answer 8

<Project>
<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>net7.0</TargetFramework>
<LangVersion>preview</LangVersion>
</PropertyGroup>
</Project>

Question 9

What is the difference between a verbatim string and an interpolated string?

Answer 9

interpolated string:
string hello = $”Hello, {name}!”;
verbatim string:
string hello = @”Hello, {name}!”;

Question 10

Raw string literal:

Answer 10

Characters enclosed in three or more double-quote characters.

Question 11

Verbatim string:

Answer 11

A literal string prefixed with @ to disable escape characters so that a backslash
is a backslash. It also allows the string value to span multiple lines because the whitespace
characters are treated as themselves instead of instructions to the compiler

Question 12

Interpolated string:

Answer 12

A literal string prefixed with $ to enable embedded formatted variables.

Question 13

sizeof()

Answer 13

returns the number of bytes that a type uses in memory

Question 14

you should only use double when…

Answer 14

you should only use double when accuracy, especially when comparing the equality of two numbers, is not important

Question 15

… suffix means a decimal literal value

Answer 15

decimal c = 0.1M;
M suffix means a decimal literal value

Question 16

The float and double types have some useful special values:

Answer 16

NaN represents not-a-number (for example,
the result of dividing by zero), Epsilon represents the smallest positive number that can be stored in
a float or double, and PositiveInfinity and NegativeInfinity represent infinitely large positive
and negative values. They also have methods for checking for these special values like IsInfinity
and IsNan.

Question 17

dynamic types

Answer 17

that can also store any type of data.
but unlike object, the value stored in the variable can have its members invoked without
an explicit cast.

Question 18

write the below variables with var keywords
int population = 67_000_000;
double weight = 1.88;
decimal price = 4.99M;
string fruit = “Apples”;
char letter = ‘Z’;
bool happy = true;

Answer 18

var population = 67_000_000;
var weight = 1.88;
var price = 4.99M;
var fruit = “Apples”;
var letter = ‘Z’;
var happy = true;

Question 19

target-typed new to instantiate objects

Answer 19

XmlDocument xml3 = new();

Question 20

Some examples of value types in C# are:

Answer 20

bool, int, long, float, byte, short, decimal, double, char, enum, struct

Question 21

Some examples of reference types in C# are:

Answer 21

object, string, dynamic, class, interface, array, delegate

Question 22

How can you write statements that will compile only for the specified platforms?

Answer 22

if NET7_0_ANDROID

// compile statements that only works on Android
#elif NET7_0_IOS
// compile statements that only works on iOS
#else
// compile statements that work everywhere else
#endif

Question 23

How to make a request for Apple’s home page?

Answer 23

HttpClient client = new();
HttpResponseMessage response = await client.GetAsync(“http://www.apple.com/”);
WriteLine(“Apple’s home page has {0:N0} bytes.”, response.Content.Headers.ContentLength);

Question 24

What statement can you type in a C# file to discover the compiler and language version?

Answer 24

error version

Question 25

How can you determine how many bytes a type like double uses in memory?

Answer 25

sizeof()