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| language | contributors | filename | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| c# |
|
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.
// Single-line comments start with //
/*
Multi-line comments look like this
*/
/// <summary>
/// This is an XML documentation comment
/// </summary>
// Specify namespaces application will be using
using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Dynamic;
using System.Linq;
using System.Linq.Expressions;
using System.Net;
using System.Threading.Tasks;
using System.IO;
// defines scope to organize code into "packages"
namespace Learning
{
// 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"));
// 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 HOURS_I_WORK_PER_WEEK = 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 }; // intialize
// 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++); //i = 1. Post-Incrementation
Console.WriteLine(++i); //i = 2. Pre-Incrementation
Console.WriteLine(i--); //i = 1. Post-Decrementation
Console.WriteLine(--i); //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>
string isTrue = (true) ? "True" : "False";
// While loop
int fooWhile = 0;
while (fooWhile < 100)
{
//Iterated 100 times, fooWhile 0->99
fooWhile++;
}
// Do While Loop
int fooDoWhile = 0;
do
{
//Iterated 100 times, fooDoWhile 0->99
fooDoWhile++;
} 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 an Exception 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();
}
///////////////////////////////////////
// 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
public static void MethodSignatures(string maxCount)
{
}
// 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());
}
public static void OtherInterestingFeatures()
{
// OPTIONAL PARAMETERS
MethodSignatures(3, 1, 3, "Some", "Extra", "Strings");
MethodSignatures(3, another: 3); // explicity set a parameter, skipping optional ones
// 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
// 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
// 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
// http://blogs.msdn.com/b/csharpfaq/archive/2010/06/01/parallel-programming-in-net-framework-4-getting-started.aspx
var websites = new string[] {
"http://www.google.com", "http://www.reddit.com",
"http://www.shaunmccarthy.com"
};
var responses = new Dictionary<string, string>();
// Will spin up separate threads for each request, and join on them
// before going to the next step!
Parallel.ForEach(websites,
new ParallelOptions() {MaxDegreeOfParallelism = 3}, // max of 3 threads
website =>
{
// Do something that takes a long time on the file
using (var r = WebRequest.Create(new Uri(website)).GetResponse())
{
responses[website] = r.ContentType;
}
});
// This won't happen till after all requests have been completed
foreach (var key in responses.Keys)
Console.WriteLine("{0}:{1}", key, responses[key]);
// 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 - combines 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 BikeRespository();
// 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 are 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 FUNCTIONS
public static void Print(this object obj)
{
Console.WriteLine(obj.ToString());
}
}
// 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 proprety
{
_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; }
// 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
// Static members belong to the type itself rather then specific object.
// You can access them without a reference to any object:
// Console.WriteLine("Bicycles created: " + Bicycle.bicyclesCreated);
static public int BicyclesCreated = 0;
// 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;
}
//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 DidWeCreateEnoughBycles()
{
// 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 ArgumentException("You can't change gears on a PennyFarthing");
}
}
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
}
// Class can inherit only one other class, but can implement any amount of interfaces
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)
/// http://msdn.microsoft.com/en-us/data/jj193542.aspx
/// </summary>
public class BikeRespository : DbSet
{
public BikeRespository()
: base()
{
}
public DbSet<Bicycle> Bikes { get; set; }
}
} // End Namespace
Topics Not Covered
- Flags
- Attributes
- Static properties
- Exceptions, Abstraction
- ASP.NET (Web Forms/MVC/WebMatrix)
- Winforms
- Windows Presentation Foundation (WPF)