This is the source code written based on the concepts explained in the Code Project C# Beginner's Article by Aisha Ikram Titled "Quick C#". This code should be helpful for the beginners to understand the following C# language features:
- Program structure
- Namespaces
- Modifiers
- Properties
- Interfaces
- Function parameters
- Arrays
- Indexers
- Boxing and unboxing
- Delegates
- Inheritance and polymorphism
For more information about the Code Project article, look into http://www.codeproject.com/csharp/quickcsharp.asp
using System;
using System.Collections.Generic;
using System.Text;
using System.Collections;
using usethis;
//Based on the C# programming concepts explained in the CodeProject Article
//http://www.codeproject.com/csharp/quickcsharp.asp
namespace FirstCSharpConsole
{
sealed class Program //sealed means no class can be inherited from this class
{
static void Main(string[] args)
{
helloworld obj = new helloworld();
obj.myVal = 10; //set property
int a = 10;
obj.func(ref a);//Pass a by reference
Console.WriteLine(a); //a will be multiplied by 10
int m;
obj.outSomething(out m);
Console.WriteLine(m);//m is out returned in the prev method as 100
obj.varparams();
obj.varparams(0, 1, 2, 3);
obj.varparams(new int[] { 1, 2, 3 });
objIsSomething(obj);
square obj1 = new square();
obj1.length = 10; //set
obj1.breadth = 20; //set
obj1.draw(obj);
Console.WriteLine(obj1.length); //get
Console.WriteLine(obj1.breadth); //get
myShape obj2 = obj1 as myShape; //"as" returns null if obj1 is NOT myShape. else returns myShape
if(obj2==null)
Console.WriteLine("square is NOT myShape");
else
Console.WriteLine("square is myShape");
Console.WriteLine("Say Hi or Hello");
obj1.playWithSwitch();
//TODO: lock: Its just like a critical section and will be needed in multi threading code
//checked and unchecked: If the below block is not in unchecked it would have raised exception
//unchecked means telling the compiler not to check for any exceptions
unchecked
{
int unch = Int32.MaxValue;
unch= unch* 2;
}
//Delegates
demoDelegates d1 = new demoDelegates();
d1.perform(10, 20);
//Virtual Functions
square s1 = new splSquare();
s1.draw(obj1);
int k = 10;
object ko = k; //boxing: package into object
int j = (int) ko; //unboxing: unpack from object
}//end of Main
private static void objIsSomething(helloworld obj)
{
if (obj is object) //all objects derive from "object"
Console.WriteLine("helloworld is object");
else
Console.WriteLine("helloworld is not object");
}
}//end of class
}//end of namespace
namespace usethis
{
class helloworld
{
int setandget; //property variable
const int need2InitHereItself = 10; //direct init
readonly int canInitHereOrInCtor = 20; //direct init
readonly int willInitInCtor;
public helloworld()
{
willInitInCtor = 30; //indirect init
canInitHereOrInCtor = 25; //reinit can be done in ctor only
canInitHereOrInCtor = 26; //reinit can be done in ctor only
}
//property is myVal
public int myVal
{
set
{
setandget = value; //note that value is a keyword
}
get
{
return setandget;
}
}
//normal method
public void func(ref int temp)
{
Console.WriteLine(this.myVal); //get property
Console.WriteLine(this.canInitHereOrInCtor);
Console.WriteLine(this.willInitInCtor);
temp = temp * 10;
//try to set readonly var
//canInitHereOrInCtor = 6999; //will give a compiler error
//try to use pointer
//int* k = new int(); //will give a compiler error
//use unsafe to write pointer code.
//Note: Need to add /unsafe in compilng options
unsafe
{
int ki = 10;
int* k = &ki; //Note: NULL is not recognised in C#
}
//Array declarations
int[] a = new int[5]; //single dimensional array
a[3] = 10;
int[,] b = new int[5, 10]; //2D array
b[0, 3] = 20;
int[][] arrayofarray = new int[2][]; //*jagged* array
arrayofarray[0] = new int[4];
arrayofarray[1] = new int[] {1,12,15};//array whose array elements are inited
//foreach: can be used to iterate in array or collection
foreach (int iter in a)
{
Console.WriteLine(iter);
}
} //end of func
//demos usage of out param
public bool outSomething(out int x)
{
x = 100;
return true;
}
//unsafe method. just for illustration, not called anywhere
public unsafe void danger()
{
int ki = 10;
int* k = &ki;
}
public void varparams(params int[] arrs)
{
Console.WriteLine("number of elements in array are {0}", arrs.Length);
}
} //end of class
interface myShape
{
int length
{
get;
set;
}
int breadth
{
get;
set;
}
void draw(object shape);
}//end of interface
//implementation class for the interface
class square : myShape
{
int sqX;
int sqY;
//get and set interface vars implemented here
public int length
{
get
{
return sqX;
}
set
{
sqX = value;
}
}
public int breadth
{
get
{
return sqY;
}
set
{
sqY = value;
}
}
//implement interface methods
public virtual void draw(object shape)
{
Console.WriteLine("interface method draw implemented here (base class)");
}
public virtual void playWithSwitch()
{
string s = Console.ReadLine();
switch (s)//strings are allowed in c# unlike c++
{
//not having break will give a compiler error
case "hi"://this is allowed
case "hello": Console.WriteLine("Hello how r u? bye"); break;
case "how r u": Console.WriteLine("I'm good thanks.bye"); break;
case "bye": Console.WriteLine("bye and have a nice day"); break;
}
}
}
class splSquare : square
{
//override will override the base class method,
//new will stop overriding the base class method
//Unlike C++, without specifying override will NOT override the base class method
//Cannot have both new and override methods for draw
public override void draw(object shape)
{
Console.WriteLine("interface method draw implemented here (derived class)");
}
//base keyword calls base class method. method is not called. this is just for demo.
public override void playWithSwitch()
{
base.playWithSwitch();
}
}
//To demonstrate indexers
class shapes : CollectionBase
{
public void add(myShape shp)
{
List.Add(shp);
}
//indexer: Indexer is used to write a method to access an element from a collection,
//by straight way of using [], like an array.
//its like overloading []
public myShape this[int index]
{
get
{
return (myShape)List[index];
}
set
{
List[index] = value;
}
}
}
class demoDelegates
{
delegate int Operation(int val1, int val2);
public int add(int val1, int val2)
{
return val1 + val2;
}
public int subtract(int val1, int val2)
{
return val1 - val2;
}
public int perform(int val1, int val2)
{
Console.WriteLine("Do you want to + or -?");
string ch = Console.ReadLine();
Operation oper;
//Delegates: Enables to conditionally(and dynamically)select the method to be invoked
if (ch == "+")
oper = new Operation(add);
else
oper = new Operation(subtract);
Console.WriteLine(oper(val1,val2));
return 0;
}
}//end of class
} //end of namespace
