Learn Microsoft C#.NET by Example

1. Hello World

using System;

public class HelloWorld {

    public static void   Main(string[] args)

    {

              

        System. Console.WriteLine("Hello World" );

        System. Console.ReadKey();

    }

}

  

2. Variables - Part I

using System;

public class Variables_I {

    public static void   Main(string[] args)

    {

              

        //A Variable is a piece of information; it has a data type and a value

          //1. Declare a variable
            //TYPE  NAME    SEMI-COLON
            int outcome;
            //COMPILE TIME ERROR: Use of unassigned local variable 'outcome'
            //System.Console.WriteLine("1. outcome=" + outcome);
 
            //2. Change the value of a variable
            //NAME  ASSIGNMENT OPERATOR VALUE   SEMI-COLON
            outcome = 42;
 
            System.Console.WriteLine("2. outcome=" + outcome);

        //another example:

        //data type: int

        //variable name: age

        //value:24

        int age=24;

        System. Console.WriteLine("My Age is " +age);

 
            string text = "hello world";
            //text = "Hello World";
            System.Console.WriteLine(text);

       
System. Console.ReadKey();

    }

}

  

3. Data Types - Part I

using System;

 public class DataTypes_I {

        public static void  Main( string[] args)

       {

           string strVar = "C# Data Types:";
 
            System.Console.WriteLine(strVar);
 

       

               byte by=129;//=>only +ive values

               short s=90;

            bool flag = true;//8 bits

            sbyte b = 2;

            int iNum = 123;//32 bits
            long lNum = 123;//64 bits
            float fNum = 123.2f;//32 bits
            double dNum = 123.2;//64 bits
            decimal DNum = 123.999m;//128 bits
            char ch = 'A';//16 bits

          //sbyte=including -ive
values



               //uint,ulong,ushort=>only +ive values




            double ans = iNum + lNum + fNum + dNum;//nb. +ch is also pssible
 
            //convert any data type into its string value by calling ToString() method
            System.Console.WriteLine(ans);
 
            //decimal  ans1 = dNum + DNum  ;//Invalid: decimal cant be mixed with double and float
            decimal ans1 = iNum + DNum;//Valid: decimal can be mixed with int and long
            System.Console.WriteLine(ans1.ToString());

//************* IMPORTANT NOTE************//

//string concatenation: using + with string will combine the number with string as text
            string str = "My age is"+10+12;//will output "My age is 1012" not "My age is 22"!
            str = "My age is" + (10 + 12);//will output "My age is 22"!

//************* IMPORTANT NOTE************//

// All numeric data types as well as char data types have two use full methods , parse and TryParse, to convert string value into 
            //primitive numeric /char types:
            int num=int.Parse("23");
            char c = char.Parse("A");
            double d = double.Parse("1.3");
            double dbl = double.Parse("ccc");//this will produce a runtime error/exception
 
            //TryParse ensures that there is no runtime error while trying to parse
            int i;
            bool Ok = int.TryParse("345", out i);//on successful parse, TryParse will put 345 in i
            bool notOk=int.TryParse("A",out i);//on failure, TryParse will put default value(0) in i

       }

 }

4. Arithmetic Operators

using System;

public class ArithmeticOperators {

        public static void  Main( string[] args)

       {

               //+-%*/++--

 
int int_ans = 1 + 3;
 
            double dbl_ans_with_unexpectedly_wrong_result = 1 / 3;
            System.Console.WriteLine("Answer:" + dbl_ans_with_unexpectedly_wrong_result);//t
 
            double dbl_ans_with_expected_result = 1 / 3.0;//any one operand MUST BE of type double!!
            System.Console.WriteLine("Answer:" + dbl_ans_with_expected_result);//t
 
            double ans = 1 + 3 * 4 - 9 / 5;//any calc that involves / or * MUST have double as result data type!
 

            System.Console.WriteLine("Answer:" + ans);//this is called string concatenation

 
            // Override precedence: Use parentheses to force ur precedence
            ans = (1 + 3) * (4 - 9) / 5;//WILL FIRST CALCULATE THE NUMBERS INSIDE THE ROUND-BRACKETS
            System.Console.WriteLine("Answer:" + ans);
 
            //mod operator: % gives only the remainder
            ans = 5 % 2;
            System.Console.WriteLine("Remainder:" + ans);
            // Increment or decrement a numeric (int/long) variable
            int outcome = 0;
            int bb = 9;
            bb = bb + outcome++;//outcome is 42
            //or
            outcome = outcome + 1;
            //same way:
            outcome--;
            outcome = outcome - 1;
 
            System.Console.WriteLine("outcome=" + outcome);//outcome has become 43
            System.Console.WriteLine("outcome=" + outcome++);//WILL ADD 1 TO outcome LATER i.e. after this use
 
            ++outcome;//WILL ADD 1 TO outcome FIRST
            System.Console.WriteLine("outcome=" + outcome);

//************* IMPORTANT NOTE************//

//+ operator can be combined with =
            int i = 6;
            i += 5;//means: i=i+5;
            //similarly:
            string str = "My name is ";
            str += "Zeeshan";//This is equvalent to str=str+"Zeeshan" and this will output "My name is Zeeshan" 

                           Console.ReadKey();

       }

 }

  

5. Boolean Operators

using System;

public class BooleanOperators {

        public static void  Main( string[] args)

       {

               //==,!=,>,<,>=,<=,!

               //e.g

               //1<=2

               //1 and 2 are called operands

               int a=3;

               int b=2;

               bool isMarried=true ;

               bool result=a>b;

               bool rs=!false ;

              rs=!isMarried;

               Console.WriteLine(isMarried);

               Console.WriteLine(rs);

bool result = 2 > 3;
            System.Console.WriteLine("result(2>3):" + result);
            result = 2 == 3;
            System.Console.WriteLine("result(2==3):" + result);
            result = 2 >= 3;
            System.Console.WriteLine("result(2>=3):" + result);
            result = 2 < 3;
            System.Console.WriteLine("result(2<3 nbsp="" span=""> + result);
            result = 2 <= 3;
            System.Console.WriteLine("result(2<=3):" + result);
            result = 2 != 3;
            System.Console.WriteLine("result(2!=3):" + result);
            result = !(true);//NOT
            System.Console.WriteLine("result(!true):" + result);
            result = !result; 

            System.Console.WriteLine("!result:" + result);               Console.ReadKey();

       }

 }

  

6. Conditions - Part I

using System;

public class Conditions_I {

        public static void  Main( string[] args)

       {

                //if (...)... else

//We use an if-statement, when we want to run a C# line of code or statement only if a condition is true
            //Syntax: if(){
            //          statement1;
            //          statement2;
            //          ...no limits...;
            //         }

        

               int age=37;

               if(age==37)

                      Console.WriteLine("You must be the Great ZEE" );

                       else if (age > 35)

                       {

                      Console.WriteLine("Assalam o Aalaikum Wr. Wbr. Bare Miyan" );

                       }

                       else

                       {

                      Console.WriteLine("Assalam o Aalaikum Wr. Wbr. Or Sultan, kia haal hen?");

                       }

int a = 2;
            if (a == 2)//will return true
                System.Console.WriteLine("a is 2");//so, for a=2, this line will execute
            if (a < 2)//will return false
                System.Console.WriteLine("a is less than 2");//now, for a<2 execute="" line="" nbsp="" span="" this="" will="">
            //Note that inside round brackets a boolean result is required
            //We can combine more than one conditions with logical operators: || or &&
            //e.g.
            if (a < 2 || a > 0)//net result will be true, because 2nd condition is true
                System.Console.WriteLine("a is less than 2 or greater than 0");//this line will execute coz a>0
            if (a > 0 && a > 2)//not both conditions are true, so net result is false
                System.Console.WriteLine("a is greater than 0 AND also greater than 2");//this line will NOT execute coz a>2 returns false
            //we can use curly-brackets optionally for a single-line execution
            if (1 == 1)
                System.Console.WriteLine("Off course! 1 is equal to 1, you fool!");
            //or
            if (1 == 1)
            {
                System.Console.WriteLine("Off course! 1 is equal to 1, you fool!");
            }
            //but when you want multiple-line execution if your condition is true, then {} are must
            bool flag = true;
            if (flag == true)//or if(flag==true)
            {
                System.Console.WriteLine("Extra Info: the word flag is generally used in programming for bool type of variables");
                System.Console.WriteLine("Agr Yeh bat samajh nhi aai to msla nahi :-)");
            }
 
            //Use 'else' when you want to execute some code if your condition fails:
            //e.g.
            string name = "Ali";//Input some string here to execute else part of condition
            if (name == "")
                System.Console.WriteLine("Empty name.");
            else
                System.Console.WriteLine("I am " + name);
            //also conditions can be 'nested if-else' like:
            if (name == "Ali")
                System.Console.WriteLine("This is my friend, " + name);
            else if (name == "Akbar")
                System.Console.WriteLine("This is my cousin, " + name);
            else if (name == "Aslam")
                System.Console.WriteLine("This is my brother, " + name);
            //... no limts...
            else //finally, if no if-statement succeeds
                System.Console.WriteLine("Who is " + name + "?");

                    Console.ReadKey();

       

       }

}

  

7. Logical Operators

using System;

 public class LogicalOperators {

        public static void  Main( string[] args)

       {

        //Example Code:

        //1. These are two operators: && and ||

        //2. We use them to apply multiple conditions by combining multiple boolean expressions:

        //e.g

        //Logical OR: ||

        bool result = 2 > 3 || 2 == 3;

        System. Console.WriteLine("result(2 > 3 || 2==3):" + result);

        //Logical AND: &&

        result = 8 > 3 && 2 < 3;

        System. Console.WriteLine("result(2 > 3 && 2==3):" + result);

       

        int i=9;

        if(i>0 && i%2==0)

                System. Console.WriteLine("Even number" );

        if(i>0 && i%3 == 0 && i%5!=0 )

                System. Console.WriteLine("Numbers that are divisible by 3 but not by 5");

        if(age>15 && age<30 amp="" sex="=</span">"MALE")

                System. Console.WriteLine("Allowed" );

        else

            System. Console.WriteLine("Not Allowed: Only Male are allowed aged 15-30");

        bool isMarried=true ;

        bool age=12;

        if(age>20 && !isMarried)

                System. Console.WriteLine("Unmarried people whose age is more  than 20");

            bool result2 = 2 > 3 || 2 == 3;
            System.Console.WriteLine("result(2 > 3 || 2==3):" + result2);
            //Logical AND: &&
            result2 = 8 > 3 && 2 < 3; 

            System.Console.WriteLine("result(2 > 3 && 2==3):" + result2);       

       }

    

 }

    

8. Casting - Part I

using System;

 public class Casting_I {

        public static void  Main( string[] args)

       {

//Casting means to convert a type into another type; this is called casting:
            //1. all smaller types can be cast into bigger types; this is called 'implicit cast'
            //2. all bigger types can be cast into smaller types; this is called 'explicit cast':
            //Syntax:
            // =()
            //e.g.
            int a = 2;
            long b = a;//this is called casting implicitly
 
            //but            
 
            //int c = b;//compile-time error:Cannot implicitly convert type 'long' to 'int'. 
 
            //so the right way is:
            int d = (int)b;//this is called casting 'explicitly'
            System.Console.WriteLine("d:" + d);

//more examples:
               byte b=2;

               int i=b;

               short s=(short )i;

              System. Console.WriteLine("Result is" +i);

               char c='a' ;

               byte ii=(byte )c;

              System. Console.WriteLine("Result of ii" +ii);

               long l=1122;

               int i2=(int )l;

              System. Console.ReadKey();

       }

    

 }

  

9. Enums

using System;

 public class Enum_Part_I {

//Enums are special types which we make ourselves 'to name some constant values'; enums can't be declared inside a method
        //Declaring an enumeration type:
        //Write the keyword enum, followed by the name of the enum , 
        //followed by a pair of curly-brackets containing 
        //a comma-separated list of the enumeration member names
        public enum Season { Spring, Summer, Fall, Winter }
        //NB. By default enumeration members have integer values according to their index/position 
        // 0 for Spring, 1 for Summer, 2 for Fall & 3 for Winter 
        //BUT, we can also assign our custom int values, like:
        public enum GradeMinimum { C = 50, B = 60, A = 70, A1 = 80 }
 
 
 
        public enum Month
        {
            January, February, March, April,
            May, June, July, August,
            September, October, November, December
            //NB. enum members can be in single/multiple lines without any semi-colon
        }
        //we can specify what type of numeric value enum members will have:
        enum MinimumAge : uint //0,1,2,3,
        {
            Children = 1, Young = 16, Old = 30
        }
        //
        enum IELTS : byte
        {
            Poor = 3, Good = 5, Excellent = 8
        }
public enum ChildrenTypes
 {
  Smart, Fat, Skinny
 }
 public enum Grades
 {
  A=80, B=70, C=60, D=50
 }
 public enum AgeRange: byte
{
  teenager=20,young=30,old=50
}

        public static void  Main( string[] args)

       {

//all enums are strings
            Console.WriteLine(Month.January); // writes out 'January'  
            Console.WriteLine(Season.Fall); // writes out 'Fall'
            //but they can be cast into int; in this case we get the index/position as an int value
            Console.WriteLine((int)Season.Fall); // writes out '2'
            //interestingly we can use enums both as a string and as an int:
            Console.WriteLine(GradeMinimum.A + " Grade's Minimum Value is " + (int)GradeMinimum.A);

 ChildrenTypes ctypes = ChildrenTypes.Fat;
  int S = (int)ChildrenTypes.Skinny;

  System.Console.WriteLine(ChildrenTypes.Smart);
  System.Console.WriteLine(Skinny);

  System.Console.WriteLine((byte)AgeRange.teenager); 
  System.Console.WriteLine((byte)Grades.D);

  System.Console.ReadKey();

 }

 } 

10. Conditions - Part II

using System;

public class Conditions_II {

        public static void  Main( string[] args)

       {

// SWITCH ...
// We can use switch to avoid many if-else if-else if-... conditions
// switch statement can check anything: strings, numbers, enums,char, etc
// every switsh case MUST have a break;
// switch last case is called default: which is the same as 'else'
            //Just as we checked 'name' variable on different possible values: Ali, Akbar, Aslam
            //Similarly, we can check variables' values by passing in a switch block like:
 
            switch (name)
            {//name could be char, bool or a numeric variable
 
                case "Ali":
                    System.Console.WriteLine("This is my friend, " + name);
                    break;//must
 
                case "Akbar":
                    System.Console.WriteLine("This is my cousin, " + name);
                    break;
 
                case "Aslam":
                    System.Console.WriteLine("This is my brother, " + name);
                    break;
                //... no limts...    
                default: //will work if all cases fail
                    System.Console.WriteLine("Who is " + name + "?");
                    break;
            }
            //NB. Enums can also be used with switch
            Month m = Month.January;
 
            switch (m)
            {
                case Month.January:
                    System.Console.WriteLine("It's very cold.");
                    break;
                case Month.June:
                    System.Console.WriteLine("It's very hot.");
                    break;
            }
 
            //NB. Enums can be compared in 3 ways:
            //an enum member versus an enum member:
            if (m == Month.January)
                System.Console.WriteLine("It's very cold.");
            else if (m == Month.June)
                System.Console.WriteLine("It's very hot.");
            //or, an int versus an enum member int value
            int userInputValue = 0;
            if (userInputValue == (int)Month.January)
                System.Console.WriteLine("It's very cold.");
            else if (userInputValue == (int)Month.June)
                System.Console.WriteLine("It's very hot.");
            //or an string versus an enum member's string value 
            string userInput = "0";
            if (userInput == Month.January.ToString())
                System.Console.WriteLine("It's very cold.");
            else if (userInput == Month.June.ToString())
                System.Console.WriteLine("It's very hot.");




//************* IMPORTANT NOTE************//



//we can combine cases by omitting their break; statement
            //this is equvalent to using ||
            int value = 2;
            switch (value)
            {
 
                case 2:
                case 3:
                case 5:
                case 6:
                    Console.WriteLine("Value accepted:"+value);
                    break;
                default:
                    Console.WriteLine("Value NOT accepted:" + value);
                    break;
            }
            //OR
            if(value==2||value==3||value==4||value==5||value==6)
                Console.WriteLine("Value accepted:" + value);
            else
                Console.WriteLine("Value NOT accepted:" + value);
          }
    }
     

11. String class methods

using System;

public class StringClass {

        public static void  Main( string[] args)

       {

// .net string class provides many useful methods to play with a string variable:

// for example:

 


   string str = "ZeE";
 
            Console.WriteLine("In the following, the sample string (str) is {0}", str);
 
            bool equals = str.Equals("zee");
            Console.WriteLine("str.Equals({0}) gives result: {1}", "zee", equals);
 
            int len = str.Length;
            Console.WriteLine("str.Length gives result: {0}", len);
 
            int compareTo = str.CompareTo("zee");//-1,0,1
            Console.WriteLine("str.CompareTo({0}) gives result: {1}", "zee", compareTo);
 
            bool contains = str.Contains("z");
            Console.WriteLine("str.Contains({0}) gives result: {1}", "z", contains);
 
            bool endsWith = str.EndsWith("E");
            Console.WriteLine("str.EndsWith({0}) gives result: {1}", "E", endsWith);
 
            int indexOfE = str.IndexOf("E");
            Console.WriteLine("str.IndexOf({0}) gives result: {1}", "E", indexOfE);
 
            int lastIndexOfE = str.LastIndexOf("E");
            Console.WriteLine("str.LastIndexOf({0}) gives result: {1}", "E", lastIndexOfE);
 
            string replace = str.Replace("Z", "z");
            Console.WriteLine("str.Replace({0},{1}) gives result: {2}", "Z", "z", replace);
 
            bool startsWithE = str.StartsWith("E");
            Console.WriteLine("str.StartsWith({0}) gives result: {1}", "E", startsWithE);
 
            string EE = str.Substring(1);
            Console.WriteLine("str.Substring({0}) gives result: {1}", 1, EE);
 
            string e = str.Substring(1, 1);
            Console.WriteLine("str.Substring({0},{1}) gives result: {2}", 1, 1, e);
 
            string zee = str.ToLower();
            Console.WriteLine("str.ToLower() gives result: {0}", zee);
 
            string ZEE = str.ToUpper();
            Console.WriteLine("str.ToUpper() gives result: {0}", ZEE);
 
            char[] strLetters = str.ToCharArray();//'Z', 'e', 'E'
 
            str = "Zee ";
            Console.WriteLine("In the following, the sample string (str) is {0}", str);
            Console.WriteLine("str Length is : {0}", str.Length);
            string Zee = str.Trim();
            Console.WriteLine("str.Trim() Length is : {0}", Zee.Length);
 
            str = "A, B, C";
            string[] comma_separated = str.Split(',');//"Cloneable"," ShadowingMember"," C"
            string[] space_separated = str.Split(' ');//"Cloneable,", "ShadowingMember,", "C"
            /**Output:
            In the following, the sample string (str) is ZeE
            str.Equals(zee) gives result: False
            str.Length gives result: 3
            str.CompareTo(zee) gives result: 1
            str.Contains(z) gives result: False
            str.EndsWith(E) gives result: True
            str.IndexOf(E) gives result: 2
            str.LastIndexOf(E) gives result: 2
            str.Replace(Z,z) gives result: zeE
            str.StartsWith(E) gives result: False
            str.Substring(1) gives result: eE
            str.Substring(1,1) gives result: e
            str.ToLower() gives result: zee
            str.ToUpper() gives result: ZEE
            In the following, the sample string (str) is Zee
            str Length is : 4
            str.Trim() Length is : 3
            **/
        }
}

12. Arrays  - Part I



public class Arrays_PartI
    {
        public static void Main(string[] args)
        {
            //creating an empty array
            byte[] marks = new byte[2];
 
            Console.WriteLine(marks[0]);//default value:0
            byte last = marks[1];//accessing an array item
 
            marks[7] = 15;//filling an array elemnt            
            Console.WriteLine(marks[7]);
 
            Console.WriteLine(last);
 
            string[] s = new string[8];//an array of eight empty strings
            s[3] = "Sultan";
            Console.WriteLine(s[3]);
 
            double[] d = new double[8];//an array of eight double numbers
 
            Console.WriteLine(d[3]);//default value: 0
 
            bool[] b = new bool[8];
 
            Console.WriteLine(b[3]);//default value: false
            Console.ReadKey();
        }
 
 
    }




13. Loops  - Part I



public class Loops_PartI
    {
        public static void Main(string[] args)
        {




   //Iteration means loops, i.e. to repeat some code for a specific no. of time

            //C# has the following four looping constructs:

            // for, foreach, while, do...while




            //FOR LOOP:

            /*

            Syntax:

            for (; ; )

            {

            ...

             statements

            ...

            }

            */

            //e.g.

            for ( int i = 0; i < 3; i++)

                System. Console.WriteLine( "i:" + i); //single-line code: no need to enclose in {}




            //we can split for-loop parts like this:

            int ii = 0;

            for (; ii < 3; )

            {

                System. Console.WriteLine( "ii:" + ii);

                ii++;

            }

            //NB. this also shows the sequence of processing:

            //1. initialize control variable (here, int ii = 0;),

            //2. execute code in {},

            //3. update control variable (here, i++),

            //4. check the status of condition (here, ii < 3)

            //NB. for multiple-lines of code {} are must



//Nested Loop : Aloop inside another loop




//e.g. This example program uses nested loop to search for vowels in a string

string aString="Zeeshan" ;

               char [] vowels= { 'a', 'e', 'o', 'u', 'i'};

        string vowelsFound= string.Empty;

           

               for ( int i =0; i

              {

                     

                      Console.WriteLine( "Checking : " +aString[i]);

                      for ( int j=0; j

                     {

                            Console.WriteLine( "With: " +vowels[j]);

                            if(aString[i]==vowels[j])

                           {

                    if(!vowelsFound.Contains(vowels[j].ToString()))

                                  vowelsFound+= ", " +vowels[j];

break ;

                           }




                     }




              }




Console .WriteLine("Vowels in {0} are {1}." ,aString,vowelsFound.Remove(0,1));



14. Math class



public class MathClass
    {
        public static void Main(string[] args)
        {


//Math class provides static methods to deal with numeric data

            int unsignedInt = Math.Abs(-2);

            Console.WriteLine( "Math.Abs({0})={1}" , -2, unsignedInt);




            double least = Math.Floor(2.4);

            Console.WriteLine( "Math.Floor({0})={1}" , 2.4, least);




            double largest = Math.Ceiling(2.4);

            Console.WriteLine( "Math.Ceiling({0})={1}" , 2.4, largest);




            int max = Math.Max(1, 2);

            Console.WriteLine( "Math.Max({0},{1})={2}" , 1, 2, max);




            int min = Math.Min(1, 2);

            Console.WriteLine( "Math.Min({0},{1})={2}" , 1, 2, min);




            double pow = Math.Pow(2, 3);

            Console.WriteLine( "Math.Pow({0},{1})={2}" , 2, 3, pow);




            double rounded = Math.Round(2.4);

            Console.WriteLine( "Math.Round({0})={1}" , 2.4, rounded);




            double sqrt = Math.Sqrt(4);

            Console.WriteLine( "Math.Sqrt({0})={1}" , 4, sqrt);

          

          /** Output:

            Math.Abs(-2)=2

            Math.Floor(2.4)=2

            Math.Ceiling(2.4)=3

            Math.Max(1,2)=2

            Math.Min(1,2)=1

            Math.Pow(2,3)=8

            Math.Round(2.4)=2

            Math.Sqrt(4)=2

             */







         }




     }



15. Object Oriented Programming (OOP) - Classes: Part I


/* Theory:

         * Object: object is our-own-defined data type which can store more than one data of some concept

         * e.g Employee, ContactInfo, Animal, Department, Cursor, System, Student, etc

         * class: a class is the coded-description of such a concept/object in a programming language

         *

         * A class may or may not be inside a namespace

         * A namespace is just a block {} with any number of classes

         * A namespace block is used to group similar type of classes

         * A name space name can contain single word or multiple words separated by .:

         * e.g. namespace MyApp{} , namespace MyApp.Classes or namespace com.zeesoft.business {}

         *

         * The description of an object (i.e. class) consists of different segments of code called class members:

         * variables, constructors,destructor,properties,methods

         *

         * Access Modifiers: C# keywords telling a programmer in which context a member can be accessed:

         * public: accessible from anywhere; within and from any other class,

         * protected: only accessible in a child class

         * internal: only accessible within a namespace,

         * private: only accessible within a class,




         * Constructors: the code-block which helps create/initialize an object;

         * it can be more than one;

         * at least one constructor is already present for all the objects

         * whether we explicitly make it or not called no-arguments constructor

         *

         * Methods: the code-blocks which process data in some way;

         * they form behavior of an object;

         * a method signature means:   ()

         * Properties: the code-blocks used to change/get variables of an object

         * Destructor: the code-block which gets called by .net Garbage Collector to release memory

         * static: variables/methods which hold data relating to all the objects of a class

         * non-static/instance: variables/methods which hold data only for a single instance/object of a class

         */



namespace OOP.Class1

{


using System;//using clauses are used to import other namespace's classes to use inside your class





    public class Person

    {




        // private variables

        int age;

        string name;

        string nick;




        // default constructor

        public Person()

        {

            Console.WriteLine( "object created by new Person()" );

            //set default values

            Name = "Name not Set" ;

        }

        // constructor with parameters/arguments

        public Person( string _name)

        {

            Console.WriteLine( "object created by new Person(name)" );

            Name = _name;

        }

        public Person( int age)

        {

            Console.WriteLine( "object created by new Person(age)" );





            Name = "Mr Unknown";

            NickName = "" ;



            this.age = age;

        }







        public Person( string _name, int age)

        {

            Console.WriteLine( "object created by new Person(name,age)" );

            name = _name;

            this.age = age;

        }




        //properties: characteristics/information/data/features of a class

        public int Age

        {

            get

            {

                return age;

            }

            set { 




                    if (isValidAge(value))

                    age= value;

                }

        }







  public bool isValidAge( int ageNum)

        {

            if (ageNum == 0 || ageNum < 0)

                return false;

            else

                return true;

        }




        public string Name

        {

            get

            {

                return name;

            }

            set { name = value; }

        }


      

       //read only property: which only has getter and no setter

        public string AgeLevel

        {

            get

            {

               



                      if (age > 0 && age <= 30)

                    return "Young " ;

                else if (age >30 )

                    return "Old " ;


                else //if (age <= 0)


                    return "" ;//unknown 



            }



        }

       //write-only property: which only has setter and no getter

        public string NickName

        {            

            set { nick= value; }

        }



        //methods: operations/actions/behavior of a class

        public void displayPersonInfo()

        {



           



if (!string .IsNullOrEmpty( this.nick))

                Console.WriteLine( "{0}{1} ({2}) is of age {3}" , AgeLevel, Name, this .nick, Age);

            else

                Console.WriteLine( "{0}{1} is of age {2}" , AgeLevel, Name,Age);



        }




       




    }




    public class Tests

    {







        public static void Main( string[] args)

        {

            Person p0 = new Person(10);

            p0.displayPersonInfo();




            Person p = new Person( "Zeeshan" , 12);

            p.NickName="ZEE";

            p.Age = 38;

            p.displayPersonInfo();




            Person p2 = new Person( "Ali" );

            p2.Age = 23;          

            p2.displayPersonInfo();




            Console.ReadKey();

        }




    }

}