C # Basics revisited

C# Basics

_____________________________________________________________

 

Variables

______________________________________________________________

 

Variables: Named value stored in memory – (case sensitive in C#)

·       Two types:

o   Value Types

§  Stores their values inside their own memory locations

§  Hold values / assigning one value type to another (literally copies values)

§  [BENS]-Bool, Enum, Numeric types, Struct (STACK storage)

o   Reference Types:

§  contains only address to the dynamic memory location where the value is stored.

§   (HEAP storage) - Objects that Stores references to the actual data

§   [CODIS] - Classes, Objects, Delegates, Interfaces Strings

Sample: employeeName

C# Reserved Variables – Keywords e.g. byte, int, async

 

Declaring Variables

   static void Main(string[] args)

        {   

            //vars         

            int a;

            double change, temperature;

          

           // Creating and initializing list

            List<int> lst = new List<int>(){2,4,6};

                     

 

            //Assign Values to Vars

            int x = 21;

            int y = x + 7;

            bool student = false;

            a = 5;

            temperature = 72.5;

 

            System.Console.WriteLine("in list:" + lst.Count);            

        }

Operators

Category	Operators
Arithmetic	+, -, *, /
Relational	== != < >= > >=
Logical	! && ||

Increment and Decrement Operators ( --  ++)

           {

               int a = 15;

               int b = ++a;

 

               int c = 20;

               int d = c++;

               System.Console.WriteLine($"a = {a} b = {b} c={c} d={d:N2}");

               //RESULT: a = 16 b = 16 c=21 d=20.00

 

                a=0;b=0;c=0;d=0; 

                a = 15;

                b = --a;

                c  =20;

                d = c--;

 

               System.Console.WriteLine($"a = {a} b = {b} c={c} d={d:N2}");

               //RESULT: a = 14 b = 14 c=19 d=20.00           

           }

 

Type Conversion

Implicit Conversion

               int x = 100;

               double y =12.55;

 

               //x = x + y; //Error: cannot implicitly convert Double to Int)

               y = x + y;

               System.Console.WriteLine(y);

               //Result:x now double -> 112.55               

 

Explicit Conversion

  

               int a = 21;

               int b =5;

               double c = (double)a / b;

               System.Console.WriteLine(c);

               //Result: 4.2

                     

Convert Class

  int r = 23;

               string s1 = Convert.ToString(r); //or

               string s2 = r.ToString(); //or

               System.Console.WriteLine($"{s1} and {s2}");

               //Result: 23 and 23

 

Input and Output in C#

            Console.WriteLine("Enter 1st number");

            double num1 = Convert.ToDouble(System.Console.ReadLine());

          

            Console.WriteLine("Enter 2nd number");

            double num2 = Convert.ToDouble(System.Console.ReadLine());

 

            var Result = num1 + num2;

            System.Console.WriteLine($"{num1} + {num2} = {Result:F2}");

            

 

 

Strings

Substring, IndexOf, LastIndexOf   

   string aString = "A basic to use in example for manipulation";

 

            string sectionWithoutLength = aString.Substring(10);

            string sectionWithLength = aString.Substring(5, 10);

 

            Console.WriteLine(sectionWithoutLength);// use in example for manipulation

            Console.WriteLine(sectionWithLength);// ic to use

 

            int charPosition = aString.IndexOf('i'); //5

 

            int stringPosition = aString.IndexOf("use");//11

            int charPosWithStartIndex = aString.IndexOf('s', 10);//12

            int stringPosWithStartIndex = aString.IndexOf("use", 10);//11

            int lastPosition = aString.LastIndexOf('o');//40

            int stringLastPosition = aString.LastIndexOf("for");//26

 

Contains, StartsWith, EndsWith

            bool containsResult = aString.Contains("use");//True

            bool startsWithResult = aString.StartsWith("bad");//False

            bool endsWithResult = aString.EndsWith("manipulation");//Treu

 

 

ToLower, ToUpper

 

  string strUp = aString.ToUpper();

            string strLo = aString.ToLower();

 

Conditions

 

Basic Condition Statements

            if (condition)

            {

               < expression2 > ;

            }

            else

            {

                < expression3 > ;

            }

 

if (condition)

            {

                < expression1 > ;            

            }

            else if (condition2)

            {

                < expression3 > ;                

            }

            else

            {

                < expression4> ;  

            }

 

Nested if

   if (condition)

            {

 

                if (condition2)

                {

                    < expression1 > ;

                }

                else

                {

                  < expression2 > ;

                }

            }

            else if (condition2)

            {

                < expression3 > ;

            }

            else

            {

                < expression4 > ;

            }

Switch-Case Statements