path: root/csharp.html.markdown

---
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"]
---

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.](http://msdn.microsoft.com/en-us/library/vstudio/z1zx9t92.aspx)

```c#
// 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;

// 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]; // 'y'
            // 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); //

            // 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 99 times, fooWhile 0->99
                fooWhile++;
            }

            // Do While Loop
            int fooDoWhile = 0;
            do
            {
                //Iterated 99 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)) // Funciton 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 MethodSignature(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

            // 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 fitler = db.Bikes.Where(b => b.HasTassles); // no query run
            if (42 > 6) // You can keep adding filters, even conditionally - great for "advanced search" functionality
                fitler = fitler.Where(b => b.IsBroken); // no query run

            var query = fitler
                .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 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 privatee
        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
        }
        // 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 mmebers 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)

## Further Reading

 * [DotNetPerls](http://www.dotnetperls.com)
 * [C# in Depth](http://manning.com/skeet2)
 * [Programming C#](http://shop.oreilly.com/product/0636920024064.do)
 * [LINQ](http://shop.oreilly.com/product/9780596519254.do)
 * [MSDN Library](http://msdn.microsoft.com/en-us/library/618ayhy6.aspx)
 * [ASP.NET MVC Tutorials](http://www.asp.net/mvc/tutorials)
 * [ASP.NET Web Matrix Tutorials](http://www.asp.net/web-pages/tutorials)
 * [ASP.NET Web Forms Tutorials](http://www.asp.net/web-forms/tutorials)
 * [Windows Forms Programming in C#](http://www.amazon.com/Windows-Forms-Programming-Chris-Sells/dp/0321116208)



[C# Coding Conventions](http://msdn.microsoft.com/en-us/library/vstudio/ff926074.aspx)