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learnxinyminutes-docs/csharp.html.markdown
Max Schumacher 6688c27025
Merge pull request #3794 from AjitZero/patch-1 
[c#/en] Updated grammar
2020-01-28 19:02:50 +01:00

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---
language: c#
contributors:
- ["Irfan Charania", "https://github.com/irfancharania"]
- ["Max Yankov", "https://github.com/golergka"]
- ["Melvyn Laïly", "http://x2a.yt"]
- ["Shaun McCarthy", "http://www.shaunmccarthy.com"]
- ["Wouter Van Schandevijl", "http://github.com/laoujin"]
- ["Jo Pearce", "http://github.com/jdpearce"]
- ["Chris Zimmerman", "https://github.com/chriszimmerman"]
- ["Shawn McGuire", "https://github.com/bigbash"]
filename: LearnCSharp.cs
---
C# is an elegant and type-safe object-oriented language that enables developers to build a variety of secure and robust applications that run on the .NET Framework.
[Read more here.](https://docs.microsoft.com/dotnet/csharp/getting-started/introduction-to-the-csharp-language-and-the-net-framework)
```c#
// Single-line comments start with //
/*
Multi-line comments look like this
*/
/// <summary>
/// This is an XML documentation comment which can be used to generate external
/// documentation or provide context help within an IDE
/// </summary>
/// <param name="firstParam">This is some parameter documentation for firstParam</param>
/// <returns>Information on the returned value of a function</returns>
public void MethodOrClassOrOtherWithParsableHelp(string firstParam) {}
// Specify the namespaces this source code will be using
// The namespaces below are all part of the standard .NET Framework Class Library
using System;
using System.Collections.Generic;
using System.Dynamic;
using System.Linq;
using System.Net;
using System.Threading.Tasks;
using System.IO;
// But this one is not:
using System.Data.Entity;
// In order to be able to use it, you need to add a dll reference
// This can be done with the NuGet package manager: `Install-Package EntityFramework`
// Namespaces define scope to organize code into "packages" or "modules"
// Using this code from another source file: using Learning.CSharp;
namespace Learning.CSharp
{
// Each .cs file should at least contain a class with the same name as the file.
// You're allowed to do otherwise, but shouldn't for sanity.
public class LearnCSharp
{
// BASIC SYNTAX - skip to INTERESTING FEATURES if you have used Java or C++ before
public static void Syntax()
{
// Use Console.WriteLine to print lines
Console.WriteLine("Hello World");
Console.WriteLine(
"Integer: " + 10 +
" Double: " + 3.14 +
" Boolean: " + true);
// To print without a new line, use Console.Write
Console.Write("Hello ");
Console.Write("World");
///////////////////////////////////////////////////
// Types & Variables
//
// Declare a variable using <type> <name>
///////////////////////////////////////////////////
// Sbyte - Signed 8-bit integer
// (-128 <= sbyte <= 127)
sbyte fooSbyte = 100;
// Byte - Unsigned 8-bit integer
// (0 <= byte <= 255)
byte fooByte = 100;
// Short - 16-bit integer
// Signed - (-32,768 <= short <= 32,767)
// Unsigned - (0 <= ushort <= 65,535)
short fooShort = 10000;
ushort fooUshort = 10000;
// Integer - 32-bit integer
int fooInt = 1; // (-2,147,483,648 <= int <= 2,147,483,647)
uint fooUint = 1; // (0 <= uint <= 4,294,967,295)
// Long - 64-bit integer
long fooLong = 100000L; // (-9,223,372,036,854,775,808 <= long <= 9,223,372,036,854,775,807)
ulong fooUlong = 100000L; // (0 <= ulong <= 18,446,744,073,709,551,615)
// Numbers default to being int or uint depending on size.
// L is used to denote that this variable value is of type long or ulong
// Double - Double-precision 64-bit IEEE 754 Floating Point
double fooDouble = 123.4; // Precision: 15-16 digits
// Float - Single-precision 32-bit IEEE 754 Floating Point
float fooFloat = 234.5f; // Precision: 7 digits
// f is used to denote that this variable value is of type float
// Decimal - a 128-bits data type, with more precision than other floating-point types,
// suited for financial and monetary calculations
decimal fooDecimal = 150.3m;
// Boolean - true & false
bool fooBoolean = true; // or false
// Char - A single 16-bit Unicode character
char fooChar = 'A';
// Strings -- unlike the previous base types which are all value types,
// a string is a reference type. That is, you can set it to null
string fooString = "\"escape\" quotes and add \n (new lines) and \t (tabs)";
Console.WriteLine(fooString);
// You can access each character of the string with an indexer:
char charFromString = fooString[1]; // => 'e'
// Strings are immutable: you can't do fooString[1] = 'X';
// Compare strings with current culture, ignoring case
string.Compare(fooString, "x", StringComparison.CurrentCultureIgnoreCase);
// Formatting, based on sprintf
string fooFs = string.Format("Check Check, {0} {1}, {0} {1:0.0}", 1, 2);
// Dates & Formatting
DateTime fooDate = DateTime.Now;
Console.WriteLine(fooDate.ToString("hh:mm, dd MMM yyyy"));
// Verbatim String
// You can use the @ symbol before a string literal to escape all characters in the string
string path = "C:\\Users\\User\\Desktop";
string verbatimPath = @"C:\Users\User\Desktop";
Console.WriteLine(path == verbatimPath); // => true
// You can split a string over two lines with the @ symbol. To escape " use ""
string bazString = @"Here's some stuff
on a new line! ""Wow!"", the masses cried";
// Use const or read-only to make a variable immutable
// const values are calculated at compile time
const int HoursWorkPerWeek = 9001;
///////////////////////////////////////////////////
// Data Structures
///////////////////////////////////////////////////
// Arrays - zero indexed
// The array size must be decided upon declaration
// The format for declaring an array is follows:
// <datatype>[] <var name> = new <datatype>[<array size>];
int[] intArray = new int[10];
// Another way to declare & initialize an array
int[] y = { 9000, 1000, 1337 };
// Indexing an array - Accessing an element
Console.WriteLine("intArray @ 0: " + intArray[0]);
// Arrays are mutable.
intArray[1] = 1;
// Lists
// Lists are used more frequently than arrays as they are more flexible
// The format for declaring a list is follows:
// List<datatype> <var name> = new List<datatype>();
List<int> intList = new List<int>();
List<string> stringList = new List<string>();
List<int> z = new List<int> { 9000, 1000, 1337 }; // initialize
// The <> are for generics - Check out the cool stuff section
// Lists don't default to a value;
// A value must be added before accessing the index
intList.Add(1);
Console.WriteLine("intList @ 0: " + intList[0]);
// Others data structures to check out:
// Stack/Queue
// Dictionary (an implementation of a hash map)
// HashSet
// Read-only Collections
// Tuple (.Net 4+)
///////////////////////////////////////
// Operators
///////////////////////////////////////
Console.WriteLine("\n->Operators");
int i1 = 1, i2 = 2; // Shorthand for multiple declarations
// Arithmetic is straightforward
Console.WriteLine(i1 + i2 - i1 * 3 / 7); // => 3
// Modulo
Console.WriteLine("11%3 = " + (11 % 3)); // => 2
// Comparison operators
Console.WriteLine("3 == 2? " + (3 == 2)); // => false
Console.WriteLine("3 != 2? " + (3 != 2)); // => true
Console.WriteLine("3 > 2? " + (3 > 2)); // => true
Console.WriteLine("3 < 2? " + (3 < 2)); // => false
Console.WriteLine("2 <= 2? " + (2 <= 2)); // => true
Console.WriteLine("2 >= 2? " + (2 >= 2)); // => true
// Bitwise operators!
/*
~ Unary bitwise complement
<< Signed left shift
>> Signed right shift
& Bitwise AND
^ Bitwise exclusive OR
| Bitwise inclusive OR
*/
// Incrementations
int i = 0;
Console.WriteLine("\n->Inc/Dec-rementation");
Console.WriteLine(i++); //Prints "0", i = 1. Post-Incrementation
Console.WriteLine(++i); //Prints "2", i = 2. Pre-Incrementation
Console.WriteLine(i--); //Prints "2", i = 1. Post-Decrementation
Console.WriteLine(--i); //Prints "0", i = 0. Pre-Decrementation
///////////////////////////////////////
// Control Structures
///////////////////////////////////////
Console.WriteLine("\n->Control Structures");
// If statements are c-like
int j = 10;
if (j == 10)
{
Console.WriteLine("I get printed");
}
else if (j > 10)
{
Console.WriteLine("I don't");
}
else
{
Console.WriteLine("I also don't");
}
// Ternary operators
// A simple if/else can be written as follows
// <condition> ? <true> : <false>
int toCompare = 17;
string isTrue = toCompare == 17 ? "True" : "False";
// While loop
int fooWhile = 0;
while (fooWhile < 100)
{
// Iterated 100 times, fooWhile 0->99
fooWhile++;
}
// Do While Loop
int fooDoWhile = 0;
do
{
// Start iteration 100 times, fooDoWhile 0->99
if (false)
continue; // skip the current iteration
fooDoWhile++;
if (fooDoWhile == 50)
break; // breaks from the loop completely
} while (fooDoWhile < 100);
// for loop structure => for(<start_statement>; <conditional>; <step>)
for (int fooFor = 0; fooFor < 10; fooFor++)
{
// Iterated 10 times, fooFor 0->9
}
// For Each Loop
// foreach loop structure => foreach(<iteratorType> <iteratorName> in <enumerable>)
// The foreach loop loops over any object implementing IEnumerable or IEnumerable<T>
// All the collection types (Array, List, Dictionary...) in the .Net framework
// implement one or both of these interfaces.
// (The ToCharArray() could be removed, because a string also implements IEnumerable)
foreach (char character in "Hello World".ToCharArray())
{
// Iterated over all the characters in the string
}
// Switch Case
// A switch works with the byte, short, char, and int data types.
// It also works with enumerated types (discussed in Enum Types),
// the String class, and a few special classes that wrap
// primitive types: Character, Byte, Short, and Integer.
int month = 3;
string monthString;
switch (month)
{
case 1:
monthString = "January";
break;
case 2:
monthString = "February";
break;
case 3:
monthString = "March";
break;
// You can assign more than one case to an action
// But you can't add an action without a break before another case
// (if you want to do this, you would have to explicitly add a goto case x
case 6:
case 7:
case 8:
monthString = "Summer time!!";
break;
default:
monthString = "Some other month";
break;
}
///////////////////////////////////////
// Converting Data Types And Typecasting
///////////////////////////////////////
// Converting data
// Convert String To Integer
// this will throw a FormatException on failure
int.Parse("123"); // returns an integer version of "123"
// try parse will default to type default on failure
// in this case: 0
int tryInt;
if (int.TryParse("123", out tryInt)) // Function is boolean
Console.WriteLine(tryInt); // 123
// Convert Integer To String
// Convert class has a number of methods to facilitate conversions
Convert.ToString(123);
// or
tryInt.ToString();
// Casting
// Cast decimal 15 to an int
// and then implicitly cast to long
long x = (int) 15M;
}
///////////////////////////////////////
// CLASSES - see definitions at end of file
///////////////////////////////////////
public static void Classes()
{
// See Declaration of objects at end of file
// Use new to instantiate a class
Bicycle trek = new Bicycle();
// Call object methods
trek.SpeedUp(3); // You should always use setter and getter methods
trek.Cadence = 100;
// ToString is a convention to display the value of this Object.
Console.WriteLine("trek info: " + trek.Info());
// Instantiate a new Penny Farthing
PennyFarthing funbike = new PennyFarthing(1, 10);
Console.WriteLine("funbike info: " + funbike.Info());
Console.Read();
} // End main method
// CONSOLE ENTRY - A console application must have a main method as an entry point
public static void Main(string[] args)
{
OtherInterestingFeatures();
}
//
// INTERESTING FEATURES
//
// DEFAULT METHOD SIGNATURES
public // Visibility
static // Allows for direct call on class without object
int // Return Type,
MethodSignatures(
int maxCount, // First variable, expects an int
int count = 0, // will default the value to 0 if not passed in
int another = 3,
params string[] otherParams // captures all other parameters passed to method
)
{
return -1;
}
// Methods can have the same name, as long as the signature is unique
// A method that differs only in return type is not unique
public static void MethodSignatures(
ref int maxCount, // Pass by reference
out int count)
{
// the argument passed in as 'count' will hold the value of 15 outside of this function
count = 15; // out param must be assigned before control leaves the method
}
// GENERICS
// The classes for TKey and TValue is specified by the user calling this function.
// This method emulates the SetDefault of Python
public static TValue SetDefault<TKey, TValue>(
IDictionary<TKey, TValue> dictionary,
TKey key,
TValue defaultItem)
{
TValue result;
if (!dictionary.TryGetValue(key, out result))
return dictionary[key] = defaultItem;
return result;
}
// You can narrow down the objects that are passed in
public static void IterateAndPrint<T>(T toPrint) where T: IEnumerable<int>
{
// We can iterate, since T is a IEnumerable
foreach (var item in toPrint)
// Item is an int
Console.WriteLine(item.ToString());
}
// YIELD
// Usage of the "yield" keyword indicates that the method it appears in is an Iterator
// (this means you can use it in a foreach loop)
public static IEnumerable<int> YieldCounter(int limit = 10)
{
for (var i = 0; i < limit; i++)
yield return i;
}
// which you would call like this :
public static void PrintYieldCounterToConsole()
{
foreach (var counter in YieldCounter())
Console.WriteLine(counter);
}
// you can use more than one "yield return" in a method
public static IEnumerable<int> ManyYieldCounter()
{
yield return 0;
yield return 1;
yield return 2;
yield return 3;
}
// you can also use "yield break" to stop the Iterator
// this method would only return half of the values from 0 to limit.
public static IEnumerable<int> YieldCounterWithBreak(int limit = 10)
{
for (var i = 0; i < limit; i++)
{
if (i > limit/2) yield break;
yield return i;
}
}
public static void OtherInterestingFeatures()
{
// OPTIONAL PARAMETERS
MethodSignatures(3, 1, 3, "Some", "Extra", "Strings");
MethodSignatures(3, another: 3); // explicitly set a parameter, skipping optional ones
// BY REF AND OUT PARAMETERS
int maxCount = 0, count; // ref params must have value
MethodSignatures(ref maxCount, out count);
// EXTENSION METHODS
int i = 3;
i.Print(); // Defined below
// NULLABLE TYPES - great for database interaction / return values
// any value type (i.e. not a class) can be made nullable by suffixing a ?
// <type>? <var name> = <value>
int? nullable = null; // short hand for Nullable<int>
Console.WriteLine("Nullable variable: " + nullable);
bool hasValue = nullable.HasValue; // true if not null
// ?? is syntactic sugar for specifying default value (coalesce)
// in case variable is null
int notNullable = nullable ?? 0; // 0
// ?. is an operator for null-propagation - a shorthand way of checking for null
nullable?.Print(); // Use the Print() extension method if nullable isn't null
// IMPLICITLY TYPED VARIABLES - you can let the compiler work out what the type is:
var magic = "magic is a string, at compile time, so you still get type safety";
// magic = 9; will not work as magic is a string, not an int
// GENERICS
//
var phonebook = new Dictionary<string, string>() {
{"Sarah", "212 555 5555"} // Add some entries to the phone book
};
// Calling SETDEFAULT defined as a generic above
Console.WriteLine(SetDefault<string,string>(phonebook, "Shaun", "No Phone")); // No Phone
// nb, you don't need to specify the TKey and TValue since they can be
// derived implicitly
Console.WriteLine(SetDefault(phonebook, "Sarah", "No Phone")); // 212 555 5555
// LAMBDA EXPRESSIONS - allow you to write code in line
Func<int, int> square = (x) => x * x; // Last T item is the return value
Console.WriteLine(square(3)); // 9
// ERROR HANDLING - coping with an uncertain world
try
{
var funBike = PennyFarthing.CreateWithGears(6);
// will no longer execute because CreateWithGears throws an exception
string some = "";
if (true) some = null;
some.ToLower(); // throws a NullReferenceException
}
catch (NotSupportedException)
{
Console.WriteLine("Not so much fun now!");
}
catch (Exception ex) // catch all other exceptions
{
throw new ApplicationException("It hit the fan", ex);
// throw; // A rethrow that preserves the callstack
}
// catch { } // catch-all without capturing the Exception
finally
{
// executes after try or catch
}
// DISPOSABLE RESOURCES MANAGEMENT - let you handle unmanaged resources easily.
// Most of objects that access unmanaged resources (file handle, device contexts, etc.)
// implement the IDisposable interface. The using statement takes care of
// cleaning those IDisposable objects for you.
using (StreamWriter writer = new StreamWriter("log.txt"))
{
writer.WriteLine("Nothing suspicious here");
// At the end of scope, resources will be released.
// Even if an exception is thrown.
}
// PARALLEL FRAMEWORK
// https://devblogs.microsoft.com/csharpfaq/parallel-programming-in-net-framework-4-getting-started/
var words = new List<string> {"dog", "cat", "horse", "pony"};
Parallel.ForEach(words,
new ParallelOptions() { MaxDegreeOfParallelism = 4 },
word =>
{
Console.WriteLine(word);
}
);
// Running this will produce different outputs
// since each thread finishes at different times.
// Some example outputs are:
// cat dog horse pony
// dog horse pony cat
// DYNAMIC OBJECTS (great for working with other languages)
dynamic student = new ExpandoObject();
student.FirstName = "First Name"; // No need to define class first!
// You can even add methods (returns a string, and takes in a string)
student.Introduce = new Func<string, string>(
(introduceTo) => string.Format("Hey {0}, this is {1}", student.FirstName, introduceTo));
Console.WriteLine(student.Introduce("Beth"));
// IQUERYABLE<T> - almost all collections implement this, which gives you a lot of
// very useful Map / Filter / Reduce style methods
var bikes = new List<Bicycle>();
bikes.Sort(); // Sorts the array
bikes.Sort((b1, b2) => b1.Wheels.CompareTo(b2.Wheels)); // Sorts based on wheels
var result = bikes
.Where(b => b.Wheels > 3) // Filters - chainable (returns IQueryable of previous type)
.Where(b => b.IsBroken && b.HasTassles)
.Select(b => b.ToString()); // Map - we only this selects, so result is a IQueryable<string>
var sum = bikes.Sum(b => b.Wheels); // Reduce - sums all the wheels in the collection
// Create a list of IMPLICIT objects based on some parameters of the bike
var bikeSummaries = bikes.Select(b=>new { Name = b.Name, IsAwesome = !b.IsBroken && b.HasTassles });
// Hard to show here, but you get type ahead completion since the compiler can implicitly work
// out the types above!
foreach (var bikeSummary in bikeSummaries.Where(b => b.IsAwesome))
Console.WriteLine(bikeSummary.Name);
// ASPARALLEL
// And this is where things get wicked - combine linq and parallel operations
var threeWheelers = bikes.AsParallel().Where(b => b.Wheels == 3).Select(b => b.Name);
// this will happen in parallel! Threads will automagically be spun up and the
// results divvied amongst them! Amazing for large datasets when you have lots of
// cores
// LINQ - maps a store to IQueryable<T> objects, with delayed execution
// e.g. LinqToSql - maps to a database, LinqToXml maps to an xml document
var db = new BikeRepository();
// execution is delayed, which is great when querying a database
var filter = db.Bikes.Where(b => b.HasTassles); // no query run
if (42 > 6) // You can keep adding filters, even conditionally - great for "advanced search" functionality
filter = filter.Where(b => b.IsBroken); // no query run
var query = filter
.OrderBy(b => b.Wheels)
.ThenBy(b => b.Name)
.Select(b => b.Name); // still no query run
// Now the query runs, but opens a reader, so only populates as you iterate through
foreach (string bike in query)
Console.WriteLine(result);
}
} // End LearnCSharp class
// You can include other classes in a .cs file
public static class Extensions
{
// EXTENSION METHODS
public static void Print(this object obj)
{
Console.WriteLine(obj.ToString());
}
}
// DELEGATES AND EVENTS
public class DelegateTest
{
public static int count = 0;
public static int Increment()
{
// increment count then return it
return ++count;
}
// A delegate is a reference to a method.
// To reference the Increment method,
// first declare a delegate with the same signature,
// i.e. takes no arguments and returns an int
public delegate int IncrementDelegate();
// An event can also be used to trigger delegates
// Create an event with the delegate type
public static event IncrementDelegate MyEvent;
static void Main(string[] args)
{
// Refer to the Increment method by instantiating the delegate
// and passing the method itself in as an argument
IncrementDelegate inc = new IncrementDelegate(Increment);
Console.WriteLine(inc()); // => 1
// Delegates can be composed with the + operator
IncrementDelegate composedInc = inc;
composedInc += inc;
composedInc += inc;
// composedInc will run Increment 3 times
Console.WriteLine(composedInc()); // => 4
// Subscribe to the event with the delegate
MyEvent += new IncrementDelegate(Increment);
MyEvent += new IncrementDelegate(Increment);
// Trigger the event
// ie. run all delegates subscribed to this event
Console.WriteLine(MyEvent()); // => 6
}
}
// Class Declaration Syntax:
// <public/private/protected/internal> class <class name>{
// //data fields, constructors, functions all inside.
// //functions are called as methods in Java.
// }
public class Bicycle
{
// Bicycle's Fields/Variables
public int Cadence // Public: Can be accessed from anywhere
{
get // get - define a method to retrieve the property
{
return _cadence;
}
set // set - define a method to set a property
{
_cadence = value; // Value is the value passed in to the setter
}
}
private int _cadence;
protected virtual int Gear // Protected: Accessible from the class and subclasses
{
get; // creates an auto property so you don't need a member field
set;
}
internal int Wheels // Internal: Accessible from within the assembly
{
get;
private set; // You can set modifiers on the get/set methods
}
int _speed; // Everything is private by default: Only accessible from within this class.
// can also use keyword private
public string Name { get; set; }
// Properties also have a special syntax for when you want a readonly property
// that simply returns the result of an expression
public string LongName => Name + " " + _speed + " speed";
// Enum is a value type that consists of a set of named constants
// It is really just mapping a name to a value (an int, unless specified otherwise).
// The approved types for an enum are byte, sbyte, short, ushort, int, uint, long, or ulong.
// An enum can't contain the same value twice.
public enum BikeBrand
{
AIST,
BMC,
Electra = 42, //you can explicitly set a value to a name
Gitane // 43
}
// We defined this type inside a Bicycle class, so it is a nested type
// Code outside of this class should reference this type as Bicycle.Brand
public BikeBrand Brand; // After declaring an enum type, we can declare the field of this type
// Decorate an enum with the FlagsAttribute to indicate that multiple values can be switched on
// Any class derived from Attribute can be used to decorate types, methods, parameters etc
// Bitwise operators & and | can be used to perform and/or operations
[Flags]
public enum BikeAccessories
{
None = 0,
Bell = 1,
MudGuards = 2, // need to set the values manually!
Racks = 4,
Lights = 8,
FullPackage = Bell | MudGuards | Racks | Lights
}
// Usage: aBike.Accessories.HasFlag(Bicycle.BikeAccessories.Bell)
// Before .NET 4: (aBike.Accessories & Bicycle.BikeAccessories.Bell) == Bicycle.BikeAccessories.Bell
public BikeAccessories Accessories { get; set; }
// Static members belong to the type itself rather than specific object.
// You can access them without a reference to any object:
// Console.WriteLine("Bicycles created: " + Bicycle.bicyclesCreated);
public static int BicyclesCreated { get; set; }
// readonly values are set at run time
// they can only be assigned upon declaration or in a constructor
readonly bool _hasCardsInSpokes = false; // read-only private
// Constructors are a way of creating classes
// This is a default constructor
public Bicycle()
{
this.Gear = 1; // you can access members of the object with the keyword this
Cadence = 50; // but you don't always need it
_speed = 5;
Name = "Bontrager";
Brand = BikeBrand.AIST;
BicyclesCreated++;
}
// This is a specified constructor (it contains arguments)
public Bicycle(int startCadence, int startSpeed, int startGear,
string name, bool hasCardsInSpokes, BikeBrand brand)
: base() // calls base first
{
Gear = startGear;
Cadence = startCadence;
_speed = startSpeed;
Name = name;
_hasCardsInSpokes = hasCardsInSpokes;
Brand = brand;
}
// Constructors can be chained
public Bicycle(int startCadence, int startSpeed, BikeBrand brand) :
this(startCadence, startSpeed, 0, "big wheels", true, brand)
{
}
// Function Syntax:
// <public/private/protected> <return type> <function name>(<args>)
// classes can implement getters and setters for their fields
// or they can implement properties (this is the preferred way in C#)
// Method parameters can have default values.
// In this case, methods can be called with these parameters omitted
public void SpeedUp(int increment = 1)
{
_speed += increment;
}
public void SlowDown(int decrement = 1)
{
_speed -= decrement;
}
// properties get/set values
// when only data needs to be accessed, consider using properties.
// properties may have either get or set, or both
private bool _hasTassles; // private variable
public bool HasTassles // public accessor
{
get { return _hasTassles; }
set { _hasTassles = value; }
}
// You can also define an automatic property in one line
// this syntax will create a backing field automatically.
// You can set an access modifier on either the getter or the setter (or both)
// to restrict its access:
public bool IsBroken { get; private set; }
// Properties can be auto-implemented
public int FrameSize
{
get;
// you are able to specify access modifiers for either get or set
// this means only Bicycle class can call set on Framesize
private set;
}
// It's also possible to define custom Indexers on objects.
// All though this is not entirely useful in this example, you
// could do bicycle[0] which returns "chris" to get the first passenger or
// bicycle[1] = "lisa" to set the passenger. (of this apparent quattrocycle)
private string[] passengers = { "chris", "phil", "darren", "regina" };
public string this[int i]
{
get {
return passengers[i];
}
set {
passengers[i] = value;
}
}
// Method to display the attribute values of this Object.
public virtual string Info()
{
return "Gear: " + Gear +
" Cadence: " + Cadence +
" Speed: " + _speed +
" Name: " + Name +
" Cards in Spokes: " + (_hasCardsInSpokes ? "yes" : "no") +
"\n------------------------------\n"
;
}
// Methods can also be static. It can be useful for helper methods
public static bool DidWeCreateEnoughBicycles()
{
// Within a static method, we only can reference static class members
return BicyclesCreated > 9000;
} // If your class only needs static members, consider marking the class itself as static.
} // end class Bicycle
// PennyFarthing is a subclass of Bicycle
class PennyFarthing : Bicycle
{
// (Penny Farthings are those bicycles with the big front wheel.
// They have no gears.)
// calling parent constructor
public PennyFarthing(int startCadence, int startSpeed) :
base(startCadence, startSpeed, 0, "PennyFarthing", true, BikeBrand.Electra)
{
}
protected override int Gear
{
get
{
return 0;
}
set
{
throw new InvalidOperationException("You can't change gears on a PennyFarthing");
}
}
public static PennyFarthing CreateWithGears(int gears)
{
var penny = new PennyFarthing(1, 1);
penny.Gear = gears; // Oops, can't do this!
return penny;
}
public override string Info()
{
string result = "PennyFarthing bicycle ";
result += base.ToString(); // Calling the base version of the method
return result;
}
}
// Interfaces only contain signatures of the members, without the implementation.
interface IJumpable
{
void Jump(int meters); // all interface members are implicitly public
}
interface IBreakable
{
bool Broken { get; } // interfaces can contain properties as well as methods & events
}
// Classes can inherit only one other class, but can implement any amount of interfaces,
// however the base class name must be the first in the list and all interfaces follow
class MountainBike : Bicycle, IJumpable, IBreakable
{
int damage = 0;
public void Jump(int meters)
{
damage += meters;
}
public bool Broken
{
get
{
return damage > 100;
}
}
}
/// <summary>
/// Used to connect to DB for LinqToSql example.
/// EntityFramework Code First is awesome (similar to Ruby's ActiveRecord, but bidirectional)
/// https://docs.microsoft.com/ef/ef6/modeling/code-first/workflows/new-database
/// </summary>
public class BikeRepository : DbContext
{
public BikeRepository()
: base()
{
}
public DbSet<Bicycle> Bikes { get; set; }
}
// Classes can be split across multiple .cs files
// A1.cs
public partial class A
{
public static void A1()
{
Console.WriteLine("Method A1 in class A");
}
}
// A2.cs
public partial class A
{
public static void A2()
{
Console.WriteLine("Method A2 in class A");
}
}
// Program using the partial class "A"
public class Program
{
static void Main()
{
A.A1();
A.A2();
}
}
// String interpolation by prefixing the string with $
// and wrapping the expression you want to interpolate with { braces }
// You can also combine both interpolated and verbatim strings with $@
public class Rectangle
{
public int Length { get; set; }
public int Width { get; set; }
}
class Program
{
static void Main(string[] args)
{
Rectangle rect = new Rectangle { Length = 5, Width = 3 };
Console.WriteLine($"The length is {rect.Length} and the width is {rect.Width}");
string username = "User";
Console.WriteLine($@"C:\Users\{username}\Desktop");
}
}
// New C# 6 features
class GlassBall : IJumpable, IBreakable
{
// Autoproperty initializers
public int Damage { get; private set; } = 0;
// Autoproperty initializers on getter-only properties
public string Name { get; } = "Glass ball";
// Getter-only autoproperty that is initialized in constructor
public string GenieName { get; }
public GlassBall(string genieName = null)
{
GenieName = genieName;
}
public void Jump(int meters)
{
if (meters < 0)
// New nameof() expression; compiler will check that the identifier exists
// nameof(x) == "x"
// Prevents e.g. parameter names changing but not updated in error messages
throw new ArgumentException("Cannot jump negative amount!", nameof(meters));
Damage += meters;
}
// Expression-bodied properties ...
public bool Broken
=> Damage > 100;
// ... and methods
public override string ToString()
// Interpolated string
=> $"{Name}. Damage taken: {Damage}";
public string SummonGenie()
// Null-conditional operators
// x?.y will return null immediately if x is null; y is not evaluated
=> GenieName?.ToUpper();
}
static class MagicService
{
private static bool LogException(Exception ex)
{
// log exception somewhere
return false;
}
public static bool CastSpell(string spell)
{
try
{
// Pretend we call API here
throw new MagicServiceException("Spell failed", 42);
// Spell succeeded
return true;
}
// Only catch if Code is 42 i.e. spell failed
catch(MagicServiceException ex) when (ex.Code == 42)
{
// Spell failed
return false;
}
// Other exceptions, or MagicServiceException where Code is not 42
catch(Exception ex) when (LogException(ex))
{
// Execution never reaches this block
// The stack is not unwound
}
return false;
// Note that catching a MagicServiceException and rethrowing if Code
// is not 42 or 117 is different, as then the final catch-all block
// will not catch the rethrown exception
}
}
public class MagicServiceException : Exception
{
public int Code { get; }
public MagicServiceException(string message, int code) : base(message)
{
Code = code;
}
}
public static class PragmaWarning {
// Obsolete attribute
[Obsolete("Use NewMethod instead", false)]
public static void ObsoleteMethod()
{
// obsolete code
}
public static void NewMethod()
{
// new code
}
public static void Main()
{
ObsoleteMethod(); // CS0618: 'ObsoleteMethod is obsolete: Use NewMethod instead'
#pragma warning disable CS0618
ObsoleteMethod(); // no warning
#pragma warning restore CS0618
ObsoleteMethod(); // CS0618: 'ObsoleteMethod is obsolete: Use NewMethod instead'
}
}
} // End Namespace
using System;
// C# 6, static using
using static System.Math;
namespace Learning.More.CSharp
{
class StaticUsing
{
static void Main()
{
// Without a static using statement..
Console.WriteLine("The square root of 4 is {}.", Math.Sqrt(4));
// With one
Console.WriteLine("The square root of 4 is {}.", Sqrt(4));
}
}
}
// New C# 7 Feature
// Install Microsoft.Net.Compilers Latest from Nuget
// Install System.ValueTuple Latest from Nuget
using System;
namespace Csharp7
{
// TUPLES, DECONSTRUCTION AND DISCARDS
class TuplesTest
{
public (string, string) GetName()
{
// Fields in tuples are by default named Item1, Item2...
var names1 = ("Peter", "Parker");
Console.WriteLine(names1.Item2); // => Parker
// Fields can instead be explicitly named
// Type 1 Declaration
(string FirstName, string LastName) names2 = ("Peter", "Parker");
// Type 2 Declaration
var names3 = (First:"Peter", Last:"Parker");
Console.WriteLine(names2.FirstName); // => Peter
Console.WriteLine(names3.Last); // => Parker
return names3;
}
public string GetLastName() {
var fullName = GetName();
// Tuples can be deconstructed
(string firstName, string lastName) = fullName;
// Fields in a deconstructed tuple can be discarded by using _
var (_, last) = fullName;
return last;
}
// Any type can be deconstructed in the same way by
// specifying a Deconstruct method
public int randomNumber = 4;
public int anotherRandomNumber = 10;
public void Deconstruct(out int randomNumber, out int anotherRandomNumber)
{
randomNumber = this.randomNumber;
anotherRandomNumber = this.anotherRandomNumber;
}
static void Main(string[] args)
{
var tt = new TuplesTest();
(int num1, int num2) = tt;
Console.WriteLine($"num1: {num1}, num2: {num2}"); // => num1: 4, num2: 10
Console.WriteLine(tt.GetLastName());
}
}
// PATTERN MATCHING
class PatternMatchingTest
{
public static (string, int)? CreateLogMessage(object data)
{
switch(data)
{
// Additional filtering using when
case System.Net.Http.HttpRequestException h when h.Message.Contains("404"):
return (h.Message, 404);
case System.Net.Http.HttpRequestException h when h.Message.Contains("400"):
return (h.Message, 400);
case Exception e:
return (e.Message, 500);
case string s:
return (s, s.Contains("Error") ? 500 : 200);
case null:
return null;
default:
return (data.ToString(), 500);
}
}
}
// REFERENCE LOCALS
// Allow you to return a reference to an object instead of just its value
class RefLocalsTest
{
// note ref in return
public static ref string FindItem(string[] arr, string el)
{
for(int i=0; i<arr.Length; i++)
{
if(arr[i] == el) {
// return the reference
return ref arr[i];
}
}
throw new Exception("Item not found");
}
public static void SomeMethod()
{
string[] arr = {"this", "is", "an", "array"};
// note refs everywhere
ref string item = ref FindItem(arr, "array");
item = "apple";
Console.WriteLine(arr[3]); // => apple
}
}
// LOCAL FUNCTIONS
class LocalFunctionTest
{
private static int _id = 0;
public int id;
public LocalFunctionTest()
{
id = generateId();
// This local function can only be accessed in this scope
int generateId()
{
return _id++;
}
}
public static void AnotherMethod()
{
var lf1 = new LocalFunctionTest();
var lf2 = new LocalFunctionTest();
Console.WriteLine($"{lf1.id}, {lf2.id}"); // => 0, 1
int id = generateId();
// error CS0103: The name 'generateId' does not exist in the current context
}
}
}
```
## Topics Not Covered
* Attributes
* async/await
* Web Development
* ASP.NET MVC & WebApi (new)
* ASP.NET Web Forms (old)
* WebMatrix (tool)
* Desktop Development
* Windows Presentation Foundation (WPF) (new)
* Winforms (old)
## Further Reading
* [C# language reference](https://docs.microsoft.com/dotnet/csharp/language-reference/)
* [Learn .NET](https://dotnet.microsoft.com/learn)
* [C# Coding Conventions](https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/inside-a-program/coding-conventions)
* [DotNetPerls](http://www.dotnetperls.com)
* [C# in Depth](http://manning.com/skeet2)
* [Programming C# 5.0](http://shop.oreilly.com/product/0636920024064.do)
* [LINQ Pocket Reference](http://shop.oreilly.com/product/9780596519254.do)
* [Windows Forms Programming in C#](http://www.amazon.com/Windows-Forms-Programming-Chris-Sells/dp/0321116208)
* [freeCodeCamp - C# Tutorial for Beginners](https://www.youtube.com/watch?v=GhQdlIFylQ8)
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