Chapter08.dib

#!markdown

# Chapter 8 - Working with Common .NET Types

Execute the following code cell to make `Console` methods available in every code cell in this notebook.

#!csharp

using static System.Console;

#!markdown

# Working with numbers

One of the most common types of data is numbers.

#!csharp

using System.Numerics;

#!markdown

## Working with big integers

#!csharp

WriteLine("Working with large integers:");
WriteLine("----------------------------------------");
ulong big = ulong.MaxValue;
WriteLine($"{big,40:N0}");
BigInteger bigger =
  BigInteger.Parse("123456789012345678901234567890");
WriteLine($"{bigger,40:N0}");

#!markdown

## Working with complex numbers

#!csharp

WriteLine("Working with complex numbers:");
Complex c1 = new(real: 4, imaginary: 2);
Complex c2 = new(real: 3, imaginary: 7);
Complex c3 = c1 + c2;
// output using default ToString implementation
WriteLine($"{c1} added to {c2} is {c3}"); // output using custom format
WriteLine("{0} + {1}i added to {2} + {3}i is {4} + {5}i",
  c1.Real, c1.Imaginary,
  c2.Real, c2.Imaginary,
  c3.Real, c3.Imaginary);

#!markdown

# Working with text

One of the other most common types of data for variables is text.

#!csharp

string city = "London";

#!markdown

## Getting the length of a string

#!csharp

WriteLine($"{city} is {city.Length} characters long.");

#!markdown

## Getting the characters of a string

#!csharp

WriteLine($"First char is {city[0]} and third is {city[2]}.");

#!markdown

## Splitting a string

#!csharp

string cities = "Paris,Tehran,Chennai,Sydney,New York,Medellín";
string[] citiesArray = cities.Split(',');
WriteLine($"There are {citiesArray.Length} items in the array.");
foreach (string item in citiesArray)
{
  WriteLine(item);
}

#!markdown

## Getting part of a string

Sometimes, you need to get part of some text. The `IndexOf` method has nine overloads that return the index position of a specified `char` or `string` within a `string`. The `Substring` method has two overloads, as shown in the following list:
- `Substring(startIndex, length)`: returns a substring starting at startIndex and containing the next length characters.
- `Substring(startIndex)`: returns a substring starting at startIndex and containing all characters up to the end of the string.

#!csharp

string fullName = "Alan Jones";
int indexOfTheSpace = fullName.IndexOf(' ');

string firstName = fullName.Substring(
  startIndex: 0, length: indexOfTheSpace);

string lastName = fullName.Substring(
  startIndex: indexOfTheSpace + 1);
  
WriteLine($"Original: {fullName}");
WriteLine($"Swapped: {lastName}, {firstName}");

#!markdown

## Checking a string for content

Sometimes, you need to check whether a piece of text starts or ends with some characters or contains some characters. You can achieve this with methods named `StartsWith`, `EndsWith`, and `Contains`:

#!csharp

string company = "Microsoft";
bool startsWithM = company.StartsWith("M");
bool containsN = company.Contains("N");
WriteLine($"Text: {company}");
WriteLine($"Starts with M: {startsWithM}, contains an N: {containsN}");

#!markdown

## Joining, formatting, and other string members

#!csharp

string recombined = string.Join(" => ", citiesArray);
WriteLine(recombined);

#!csharp

string fruit = "Apples";
decimal price =  0.39M;
DateTime when = DateTime.Today;
WriteLine($"Interpolated:  {fruit} cost {price:C} on {when:dddd}.");
WriteLine(string.Format("string.Format: {0} cost {1:C} on {2:dddd}.",
  arg0: fruit, arg1: price, arg2: when));

#!markdown

# Working with dates and times

After numbers and text, the next most popular types of data to work with are dates and times.

#!markdown

## Specifying date and time values

#!csharp

WriteLine("Earliest date/time value is: {0}",
  arg0: DateTime.MinValue);
WriteLine("UNIX epoch date/time value is: {0}",
  arg0: DateTime.UnixEpoch);
WriteLine("Date/time value Now is: {0}",
  arg0: DateTime.Now);
WriteLine("Date/time value Today is: {0}",
  arg0: DateTime.Today);

#!csharp

DateTime christmas = new(year: 2021, month: 12, day: 25);

WriteLine("Christmas: {0}",
  arg0: christmas); // default format 

WriteLine("Christmas: {0:dddd, dd MMMM yyyy}",
  arg0: christmas); // custom format 

WriteLine("Christmas is in month {0} of the year.",
  arg0: christmas.Month);

WriteLine("Christmas is day {0} of the year.",
  arg0: christmas.DayOfYear);
  
WriteLine("Christmas {0} is on a {1}.",
  arg0: christmas.Year,
  arg1: christmas.DayOfWeek);

#!csharp

DateTime beforeXmas = christmas.Subtract(TimeSpan.FromDays(12));
DateTime afterXmas = christmas.AddDays(12);

WriteLine("12 days before Christmas is: {0}",
  arg0: beforeXmas);

WriteLine("12 days after Christmas is: {0}",
  arg0: afterXmas);

TimeSpan untilChristmas = christmas - DateTime.Now;

WriteLine("There are {0} days and {1} hours until Christmas.",
  arg0: untilChristmas.Days,
  arg1: untilChristmas.Hours);
  
WriteLine("There are {0:N0} hours until Christmas.",
  arg0: untilChristmas.TotalHours);

#!csharp

DateTime kidsWakeUp = new(
  year: 2021, month: 12, day: 25,
  hour: 6, minute: 30, second: 0);

WriteLine("Kids wake up on Christmas: {0}",
  arg0: kidsWakeUp);
  
WriteLine("The kids woke me up at {0}",
  arg0: kidsWakeUp.ToShortTimeString());

#!markdown

## Globalization with dates and times

The current culture controls how dates and times are parsed:

#!csharp

using System.Globalization;

#!csharp

// use the following line to switch to British culture
CultureInfo.CurrentCulture = CultureInfo.GetCultureInfo("en-GB");

WriteLine("Current culture is: {0}",
  arg0: CultureInfo.CurrentCulture.Name);

string textDate = "4 July 2021";
DateTime independenceDay = DateTime.Parse(textDate);

WriteLine("Text: {0}, DateTime: {1:d MMMM}",
  arg0: textDate,
  arg1: independenceDay);

textDate = "7/4/2021";
independenceDay = DateTime.Parse(textDate);

WriteLine("Text: {0}, DateTime: {1:d MMMM}",
  arg0: textDate,
  arg1: independenceDay);

independenceDay = DateTime.Parse(textDate,
  provider: CultureInfo.GetCultureInfo("en-US"));

WriteLine("Text: {0}, DateTime: {1:d MMMM}",
  arg0: textDate,
  arg1: independenceDay);

#!csharp

for (int year = 2020; year < 2026; year++)
{
  Write($"{year} is a leap year: {DateTime.IsLeapYear(year)}. ");
  WriteLine("There are {0} days in February {1}.",
    arg0: DateTime.DaysInMonth(year: year, month: 2), arg1: year);
}
WriteLine("Is Christmas daylight saving time? {0}",
  arg0: christmas.IsDaylightSavingTime());
  
WriteLine("Is July 4th daylight saving time? {0}",
  arg0: independenceDay.IsDaylightSavingTime());

#!markdown

## Working with only a date or a time

.NET 6 introduces some new types for working with only a date value or only a time value named DateOnly and TimeOnly.

#!csharp

DateOnly queensBirthday = new(year: 2022, month: 4, day: 21);
WriteLine($"The Queen's next birthday is on {queensBirthday}.");

TimeOnly partyStarts = new(hour: 20, minute: 30);
WriteLine($"The Queen's party starts at {partyStarts}.");

DateTime calendarEntry = queensBirthday.ToDateTime(partyStarts);
WriteLine($"Add to your calendar: {calendarEntry}.");

#!markdown

# Pattern matching with regular expressions

Regular expressions are useful for validating input from the user. 

#!csharp

using System.Text.RegularExpressions;

#!markdown

## Checking for digits entered as text

#!csharp

#nullable enable // required to support string?

// Write("Enter your age: ");
string? input = "34"; // ReadLine();

Regex ageChecker = new(@"^\d+$");

if (ageChecker.IsMatch(input))
{
  WriteLine("Thank you!");
}
else
{
  WriteLine($"This is not a valid age: {input}");
}

#!markdown

## Splitting a complex comma-separated string

Earlier in this chapter, you learned how to split a simple comma-separated `string` variable. But what about the following example of film titles?
```
  "Monsters, Inc.","I, Tonya","Lock, Stock and Two Smoking Barrels"
```

#!csharp

string films = "\"Monsters, Inc.\",\"I, Tonya\",\"Lock, Stock and Two Smoking Barrels\"";

WriteLine($"Films to split: {films}");

string[] filmsDumb = films.Split(',');

WriteLine("Splitting with string.Split method:");
foreach (string film in filmsDumb)
{
  WriteLine(film);
}

#!csharp

WriteLine();

Regex csv = new(
  "(?:^|,)(?=[^\"]|(\")?)\"?((?(1)[^\"]*|[^,\"]*))\"?(?=,|$)");

MatchCollection filmsSmart = csv.Matches(films);

WriteLine("Splitting with regular expression:");
foreach (Match film in filmsSmart)
{
  WriteLine(film.Groups[2].Value);
}

#!markdown

# Storing multiple objects in collections

Another of the most common types of data is collections. If you need to store multiple values in a variable, then you can use a collection.

#!csharp

static void Output(string title, IEnumerable<string> collection)
{
  WriteLine(title);
  foreach (string item in collection)
  {
    WriteLine($"  {item}");
  } 
}

#!markdown

## Working with lists

#!csharp

static void WorkingWithLists()
{
  // Simple syntax for creating a list and adding three items
  List<string> cities = new();
  cities.Add("London");
  cities.Add("Paris");
  cities.Add("Milan");

  /* Alternative syntax that is converted by the compiler into
     the three Add method calls above
  List<string> cities = new()
    { "London", "Paris", "Milan" }; 
  */

  /* Alternative syntax that passes an
     array of string values to AddRange method
  List<string> cities = new();
  cities.AddRange(new[] { "London", "Paris", "Milan" });
  */

  Output("Initial list", cities);
  WriteLine($"The first city is {cities[0]}.");
  WriteLine($"The last city is {cities[cities.Count - 1]}.");
  cities.Insert(0, "Sydney");
  Output("After inserting Sydney at index 0", cities);
  cities.RemoveAt(1);
  cities.Remove("Milan");
  Output("After removing two cities", cities);
}

#!csharp

WorkingWithLists();

#!markdown

## Working with dictionaries

#!csharp

static void WorkingWithDictionaries()
{
  Dictionary<string, string> keywords = new(); 
  
  // add using named parameters
  keywords.Add(key: "int", value: "32-bit integer data type");

  // add using positional parameters
  keywords.Add("long", "64-bit integer data type");
  keywords.Add("float", "Single precision floating point number");
  
  /* Alternative syntax; compiler converts this to calls to Add method
  Dictionary<string, string> keywords = new()
  {
    { "int", "32-bit integer data type" },
    { "long", "64-bit integer data type" },
    { "float", "Single precision floating point number" },
  }; */

  /* Alternative syntax; compiler converts this to calls to Add method
  Dictionary<string, string> keywords = new()
  {
    ["int"] = "32-bit integer data type",
    ["long"] = "64-bit integer data type",
    ["float"] = "Single precision floating point number"
  }; */

  Output("Dictionary keys:", keywords.Keys);
  Output("Dictionary values:", keywords.Values);

  WriteLine("Keywords and their definitions");
  foreach (KeyValuePair<string, string> item in keywords)
  {
    WriteLine($"  {item.Key}: {item.Value}");
  }
  
  // lookup a value using a key
  string key = "long";
  WriteLine($"The definition of {key} is {keywords[key]}");
}

#!csharp

WorkingWithDictionaries();

#!markdown

## Working with queues

#!csharp

static void WorkingWithQueues()
{
  Queue<string> coffee = new();

  coffee.Enqueue("Damir"); // front of queue 
  coffee.Enqueue("Andrea"); 
  coffee.Enqueue("Ronald"); 
  coffee.Enqueue("Amin"); 
  coffee.Enqueue("Irina"); // back of queue

  Output("Initial queue from front to back", coffee);

  // server handles next person in queue
  string served = coffee.Dequeue();
  WriteLine($"Served: {served}.");

  // server handles next person in queue
  served = coffee.Dequeue();
  WriteLine($"Served: {served}.");

  Output("Current queue from front to back", coffee);

  WriteLine($"{coffee.Peek()} is next in line.");
  
  Output("Current queue from front to back", coffee);
}

#!csharp

WorkingWithQueues();

#!csharp

static void OutputPQ<TElement, TPriority>(string title,
  IEnumerable<(TElement Element, TPriority Priority)> collection)
{
  WriteLine(title);
  foreach ((TElement, TPriority) item in collection)
  {
    WriteLine($"  {item.Item1}: {item.Item2}");
  }
}

#!csharp

static void WorkingWithPriorityQueues()
{
  PriorityQueue<string, int> vaccine = new();

  // add some people
  // 1 = high priority people in their 70s or poor health 
  // 2 = medium priority e.g. middle aged
  // 3 = low priority e.g. teens and twenties 
  vaccine.Enqueue("Pamela", 1); // my mum (70s) 
  vaccine.Enqueue("Rebecca", 3); // my niece (teens) 
  vaccine.Enqueue("Juliet", 2); // my sister (40s) 
  vaccine.Enqueue("Ian", 1); // my dad (70s)

  OutputPQ("Current queue for vaccination:", vaccine.UnorderedItems);

  WriteLine($"{vaccine.Dequeue()} has been vaccinated.");
  WriteLine($"{vaccine.Dequeue()} has been vaccinated.");

  OutputPQ("Current queue for vaccination:", vaccine.UnorderedItems);

  WriteLine($"{vaccine.Dequeue()} has been vaccinated."); 
  vaccine.Enqueue("Mark", 2); // me (40s)
  WriteLine($"{vaccine.Peek()} will be next to be vaccinated.");
  OutputPQ("Current queue for vaccination:", vaccine.UnorderedItems);
}

#!csharp

WorkingWithPriorityQueues();

#!markdown

## Using immutable collections

#!csharp

using System.Collections.Immutable;

#!csharp

static void WorkingWithLists2()
{
  // Simple syntax for creating a list and adding three items
  List<string> cities = new();
  cities.Add("London");
  cities.Add("Paris");
  cities.Add("Milan");

  /* Alternative syntax that is converted by the compiler into
     the three Add method calls above
  List<string> cities = new()
    { "London", "Paris", "Milan" }; 
  */

  /* Alternative syntax that passes an
     array of string values to AddRange method
  List<string> cities = new();
  cities.AddRange(new[] { "London", "Paris", "Milan" });
  */

  Output("Initial list", cities);
  WriteLine($"The first city is {cities[0]}.");
  WriteLine($"The last city is {cities[cities.Count - 1]}.");
  cities.Insert(0, "Sydney");
  Output("After inserting Sydney at index 0", cities);
  cities.RemoveAt(1);
  cities.Remove("Milan");
  Output("After removing two cities", cities);

  ImmutableList<string> immutableCities = cities.ToImmutableList();
  ImmutableList<string> newList = immutableCities.Add("Rio");

  Output("Immutable list of cities:", immutableCities);
  Output("New list of cities:", newList);
}

#!csharp

WorkingWithLists2();

#!markdown

# Working with spans, indexes, and ranges

C# 8.0 introduced two features for identifying an item's index within an array and a range of items using two indexes.

#!markdown

## Identifying ranges with the Range type

#!csharp

Range r1 = new(start: new Index(3), end: new Index(7));
Range r2 = new(start: 3, end: 7); // using implicit int conversion 
Range r3 = 3..7; // using C# 8.0 or later syntax
Range r4 = Range.StartAt(3); // from index 3 to last index
Range r5 = 3..; // from index 3 to last index
Range r6 = Range.EndAt(3); // from index 0 to index 3
Range r7 = ..3; // from index 0 to index 3

#!markdown

## Using indexes, ranges, and spans

#!csharp

string name = "Samantha Jones"; 

// Using Substring

int lengthOfFirst = name.IndexOf(' ');
int lengthOfLast = name.Length - lengthOfFirst - 1;

string firstName = name.Substring(
  startIndex: 0,
  length: lengthOfFirst);

string lastName = name.Substring(
  startIndex: name.Length - lengthOfLast,
  length: lengthOfLast);

WriteLine($"First name: {firstName}, Last name: {lastName}"); 

// Using spans

ReadOnlySpan<char> nameAsSpan = name.AsSpan();
ReadOnlySpan<char> firstNameSpan = nameAsSpan[0..lengthOfFirst];
ReadOnlySpan<char> lastNameSpan = nameAsSpan[^lengthOfLast..^0];

WriteLine("First name: {0}, Last name: {1}",
  arg0: firstNameSpan.ToString(),
  arg1: lastNameSpan.ToString());

#!markdown

# Working with network resources

Sometimes you will need to work with network resources.

#!markdown

## Working with URIs, DNS, and IP addresses

#!csharp

using System.Net; // IPHostEntry, Dns, IPAddress

#!csharp

#nullable enable

// Write("Enter a valid web address: ");
string? url = "http://google.com"; // ReadLine();

if (string.IsNullOrWhiteSpace(url))
{
  url = "https://stackoverflow.com/search?q=securestring";
}

Uri uri = new(url);

WriteLine($"URL: {url}");
WriteLine($"Scheme: {uri.Scheme}");
WriteLine($"Port: {uri.Port}");
WriteLine($"Host: {uri.Host}");
WriteLine($"Path: {uri.AbsolutePath}");
WriteLine($"Query: {uri.Query}");

#!csharp

IPHostEntry entry = Dns.GetHostEntry(uri.Host);
WriteLine($"{entry.HostName} has the following IP addresses:");
foreach (IPAddress address in entry.AddressList)
{
  WriteLine($" {address} ({address.AddressFamily})");
}

#!markdown

## Pinging a server

#!csharp

using System.Net.NetworkInformation; // Ping, PingReply, IPStatus

#!csharp

try
{
  Ping ping = new();
  WriteLine("Pinging server. Please wait...");
  PingReply reply = ping.Send(uri.Host);

  WriteLine($"{uri.Host} was pinged and replied: {reply.Status}.");
  if (reply.Status == IPStatus.Success)
  {
    WriteLine("Reply from {0} took {1:N0}ms",
      arg0: reply.Address,
      arg1: reply.RoundtripTime);
  }
}
catch (Exception ex)
{
  WriteLine($"{ex.GetType().ToString()} says {ex.Message}");
}

#!markdown

# Working with reflection and attributes

Reflection is a programming feature that allows code to understand and manipulate itself.

#!csharp

using System.Reflection; // Assembly

#!markdown

## Reading assembly metadata

Note: This example works best in a console application. In a .NET Interactive notebook, the assembly is `Microsoft.DotNet.Interactive.App`.

#!csharp

#nullable enable

WriteLine("Assembly metadata:");
Assembly? assembly = Assembly.GetEntryAssembly();
if (assembly is null)
{
  WriteLine("Failed to get entry assembly.");
  return;
}

WriteLine($" Full name: {assembly.FullName}");
WriteLine($" Location: {assembly.Location}");

IEnumerable<Attribute> attributes = assembly.GetCustomAttributes();

WriteLine($" Assembly-level attributes:");
foreach (Attribute a in attributes)
{
  WriteLine($" {a.GetType()}");
}

#!csharp

#nullable enable

AssemblyInformationalVersionAttribute? version = assembly
  .GetCustomAttribute<AssemblyInformationalVersionAttribute>();

WriteLine($" Version: {version?.InformationalVersion}");

AssemblyCompanyAttribute? company = assembly
  .GetCustomAttribute<AssemblyCompanyAttribute>();
  
WriteLine($" Company: {company?.Company}");

#!markdown

## Creating custom attributes

This section should only be tried in a console application.

#!markdown

# Working with images

ImageSharp is a third-party cross-platform 2D graphics library.

#!csharp

#r "nuget:SixLabors.ImageSharp,1.0.3"

#!csharp

using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Processing;
using System.IO;

#!csharp

string imagesFolder = Path.Combine(
  Environment.CurrentDirectory, "images");

IEnumerable<string> images =
  Directory.EnumerateFiles(imagesFolder);

foreach (string imagePath in images)
{
  string thumbnailPath = Path.Combine(
    Environment.CurrentDirectory, "images",
    Path.GetFileNameWithoutExtension(imagePath)
    + "-thumbnail" + Path.GetExtension(imagePath));

  using (Image image = Image.Load(imagePath))
  {
    image.Mutate(x => x.Resize(image.Width / 10, image.Height / 10));
    image.Mutate(x => x.Grayscale());
    image.Save(thumbnailPath);
  }
}
WriteLine("Image processing complete. View the images folder.");

#!markdown

# Internationalizing your code

#!csharp

using System.Globalization; // CultureInfo

#!csharp

#nullable enable

CultureInfo globalization = CultureInfo.CurrentCulture;
CultureInfo localization = CultureInfo.CurrentUICulture;

WriteLine("The current globalization culture is {0}: {1}",
  globalization.Name, globalization.DisplayName);

WriteLine("The current localization culture is {0}: {1}",
  localization.Name, localization.DisplayName);

WriteLine();

WriteLine("en-US: English (United States)");
WriteLine("da-DK: Danish (Denmark)");
WriteLine("fr-CA: French (Canada)");

// Write("Enter an ISO culture code: ");
string? newCulture = "da-DK"; // ReadLine();

if (!string.IsNullOrEmpty(newCulture))
{
  CultureInfo ci = new(newCulture);

  // change the current cultures
  CultureInfo.CurrentCulture = ci;
  CultureInfo.CurrentUICulture = ci;
}
WriteLine();

// Write("Enter your name: ");
string? name = "Mikkel"; // ReadLine();

// Write("Enter your date of birth: ");
string? dob = "12/3/1980"; // ReadLine();

// Write("Enter your salary: ");
string? salary = "340000"; // ReadLine();

DateTime date = DateTime.Parse(dob);
int minutes = (int)DateTime.Today.Subtract(date).TotalMinutes;
decimal earns = decimal.Parse(salary);

WriteLine(
  "{0} was born on a {1:dddd}, is {2:N0} minutes old, and earns {3:C}",
  name, date, minutes, earns);