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learnxinyminutes-docs/csharp.html.markdown
Max Yankov a225349acb C#: interfaces
2013-08-17 23:28:55 +02:00

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---
language: c#
contributors:
- ["Irfan Charania", "https://github.com/irfancharania"]
- ["Max Yankov", "https://github.com/golergka"]
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.](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;
// 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
{
// A console application must have a main method as an entry point
public static void Main(string[] args)
{
// 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 - Signed 16-bit integer
// (-32,768 <= short <= 32,767)
short fooShort = 10000;
// Ushort - Unsigned 16-bit integer
// (0 <= ushort <= 65,535)
ushort fooUshort = 10000;
// Integer - Signed 32-bit integer
// (-2,147,483,648 <= int <= 2,147,483,647)
int fooInt = 1;
// Uinteger - Unsigned 32-bit integer
// (0 <= uint <= 4,294,967,295)
uint fooUint = 1;
// Long - Signed 64-bit integer
// (-9,223,372,036,854,775,808 <= long <= 9,223,372,036,854,775,807)
long fooLong = 100000L;
// L is used to denote that this variable value is of type long or ulong
// anything without is treated as int or uint depending on size.
// Ulong - Unsigned 64-bit integer
// (0 <= ulong <= 18,446,744,073,709,551,615)
ulong fooUlong = 100000L;
// Float - Single-precision 32-bit IEEE 754 Floating Point
// Precision: 7 digits
float fooFloat = 234.5f;
// f is used to denote that this variable value is of type float;
// otherwise it is treated as double.
// Double - Double-precision 64-bit IEEE 754 Floating Point
// Precision: 15-16 digits
double fooDouble = 123.4;
// Bool - true & false
bool fooBoolean = true;
bool barBoolean = false;
// Char - A single 16-bit Unicode character
char fooChar = 'A';
// Strings
string fooString = "My string is here!";
Console.WriteLine(fooString);
// formatting
string fooFs = string.Format("Check Check, {0} {1}, {0} {1:0.0}", 1, 2);
Console.WriteLine(fooFormattedString);
// formatting dates
DateTime fooDate = DateTime.Now;
Console.WriteLine(fooDate.ToString("hh:mm, dd MMM yyyy"));
// \n is an escaped character that starts a new line
string barString = "Printing on a new line?\nNo Problem!";
Console.WriteLine(barString);
// it can be written prettier by using the @ symbol
string bazString = @"Here's some stuff
on a new line!";
Console.WriteLine(bazString);
// quotes need to be escaped
// use \" normally
string quotedString = "some \"quoted\" stuff";
Console.WriteLine(quotedString);
// use "" when strings start with @
string quotedString2 = @"some MORE ""quoted"" stuff";
Console.WriteLine(quotedString2);
// 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;
// Nullable types
// any type can be made nullable by suffixing a ?
// <type>? <var name> = <value>
int? nullable = null;
Console.WriteLine("Nullable variable: " + nullable);
// In order to use nullable's value, you have to use Value property or to explicitly cast it
string? nullableString = "not null";
Console.WriteLine("Nullable value is: " + nullableString.Value + " or: " + (string) nullableString );
// ?? is syntactic sugar for specifying default value
// in case variable is null
int notNullable = nullable ?? 0;
Console.WriteLine("Not nullable variable: " + notNullable);
// Var - compiler will choose the most appropriate type based on value
var fooImplicit = true;
///////////////////////////////////////////////////
// Data Structures
///////////////////////////////////////////////////
Console.WriteLine("\n->Data Structures");
// Arrays
// 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];
string[] stringArray = new string[1];
bool[] boolArray = new bool[100];
// 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 zero-indexed and mutable.
intArray[1] = 1;
Console.WriteLine("intArray @ 1: " + 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>();
// Another way to declare & initialize a list
List<int> z = new List<int> { 9000, 1000, 1337 };
// Indexing a list - Accessing an element
// Lists are zero-indexed and mutable.
Console.WriteLine("z @ 0: " + z[2]);
// 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
// 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("1+2 = " + (i1 + i2)); // => 3
Console.WriteLine("2-1 = " + (i2 - i1)); // => 1
Console.WriteLine("2*1 = " + (i2 * i1)); // => 2
Console.WriteLine("1/2 = " + (i1 / i2)); // => 0 (0.5 truncated down)
// 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
>>> Unsigned 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";
Console.WriteLine("Ternary demo: " + isTrue);
// While loop
int fooWhile = 0;
while (fooWhile < 100)
{
//Console.WriteLine(fooWhile);
//Increment the counter
//Iterated 99 times, fooWhile 0->99
fooWhile++;
}
Console.WriteLine("fooWhile Value: " + fooWhile);
// Do While Loop
int fooDoWhile = 0;
do
{
//Console.WriteLine(fooDoWhile);
//Increment the counter
//Iterated 99 times, fooDoWhile 0->99
fooDoWhile++;
} while (fooDoWhile < 100);
Console.WriteLine("fooDoWhile Value: " + fooDoWhile);
// For Loop
int fooFor;
//for loop structure => for(<start_statement>; <conditional>; <step>)
for (fooFor = 0; fooFor < 10; fooFor++)
{
//Console.WriteLine(fooFor);
//Iterated 10 times, fooFor 0->9
}
Console.WriteLine("fooFor Value: " + fooFor);
// 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;
default:
monthString = "Some other month";
break;
}
Console.WriteLine("Switch Case Result: " + monthString);
///////////////////////////////////////
// Converting Data Types And Typcasting
///////////////////////////////////////
// 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;
int.TryParse("123", out tryInt);
// Convert Integer To String
// Convert class has a number of methods to facilitate conversions
Convert.ToString(123);
///////////////////////////////////////
// Classes And Functions
///////////////////////////////////////
Console.WriteLine("\n->Classes & Functions");
// (definition of the Bicycle class follows)
// 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.setCadence(100);
// ToString is a convention to display the value of this Object.
Console.WriteLine("trek info: " + trek.ToString());
// Instantiate another new Bicycle
Bicycle octo = new Bicycle(5, 10);
Console.WriteLine("octo info: " + octo.ToString());
// Instantiate a new Penny Farthing
PennyFarthing funbike = new PennyFarthing(1, 10);
Console.WriteLine("funbike info: " + funbike.ToString());
Console.Read();
} // End main method
} // End LearnCSharp class
// You can include other classes in a .cs file
// Class Declaration Syntax:
// <public/private/protected> 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
private int _speed; // Private: Only accessible from within the class
protected int gear; // Protected: Accessible from the class and subclasses
internal int wheels; // Internal: Accessible from within the assembly
string name; // Everything is private by default: Only accessible from within this class
// Enum is a value type that consists of a set of named constants
public enum Brand
{
AIST,
BMC,
Electra,
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 Brand brand; // After declaing an enum type, we can declare the field of this type
// Static members belong to the type itself rather then specific object.
static public int bicyclesCreated = 0;
// You can access them without a reference to any object:
// Console.WriteLine("Bicycles created: " + Bicycle.bicyclesCreated);
// 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
private Bicycle()
{
gear = 1;
cadence = 50;
_speed = 5;
name = "Bontrager";
brand = Brand.AIST;
bicyclesCreated++;
}
// This is a specified constructor (it contains arguments)
public Bicycle(int startCadence, int startSpeed, int startGear,
string name, bool hasCardsInSpokes, Brand brand)
{
this.gear = startGear; // "this" keyword denotes the current object
this.cadence = startCadence;
this._speed = startSpeed;
this.name = name; // it can be useful when there's a name conflict
this.hasCardsInSpokes = hasCardsInSpokes;
this.brand = brand;
}
// Constructors can be chained
public Bicycle(int startCadence, int startSpeed, Brand brand) :
this(startCadence, startSpeed, 0, "big wheels", true)
{
}
// Function Syntax:
// <public/private/protected> <return type> <function name>(<args>)
// classes can implement getters and setters for their fields
// or they can implement properties
// Method declaration syntax:
// <scope> <return type> <method name>(<args>)
public int GetCadence()
{
return cadence;
}
// void methods require no return statement
public void SetCadence(int newValue)
{
cadence = newValue;
}
// virtual keyword indicates this method can be overridden
public virtual void SetGear(int newValue)
{
gear = newValue;
}
// Method parameters can have defaut 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; }
}
// 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 override string ToString()
{
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 memebers
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)
{
}
public override void SetGear(int gear)
{
gear = 0;
}
public override string ToString()
{
string result = "PennyFarthing bicycle ";
result += base.ToString(); // Calling the base version of the method
return reuslt;
}
}
// 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, fields & 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 void Broken
{
get
{
return damage > 100;
}
}
}
} // End Namespace
```
## Topics Not Covered
* Flags
* Attributes
* Generics (T), Delegates, Func, Actions, lambda expressions
* Static properties
* Exceptions, Abstraction
* LINQ
* 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)
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