SQL server database connection in Window Form

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I will start first Tutorial with SQL server database connection. Here i will explain step by step. follow these steps.
step (1):- create a window form
Open visual stdio and create a new project and select window form application and give it name as First_Csharp app.

step (2):- Drag and down a button
now from tool box drag and down a button and click on button

step (3):-Database table
create a database table in sql server. here database name is windowapp and tablename is data

step (4):-Coding on button click
first insert a namespace "using System.Data.SqlClient".

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Text;

using System.Windows.Forms;

using System.Data.SqlClient;

namespace First_Csharp_app

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }

        private void button1_Click(object sender, EventArgs e)

        {

            try

            {

                String str = "server=MUNESH-PC;database=windowapp;UID=sa;password=123";

                String query = "select * from data";

                SqlConnection con = new SqlConnection(str);

                SqlCommand cmd = new SqlCommand(query, con);

                con.Open();

                DataSet ds = new DataSet();

                MessageBox.Show("connect with sql server");

                con.Close();

            }

            catch (Exception es)

            {

                MessageBox.Show(es.Message);

            }

        }

    }

} 

step (5):-Run the application 

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Properties in C#

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Properties are special kind of class member, In Properties we use predefined Set or Get method.They use accessors through which we can read, written or change the values of the private fields.

For example, let us Take a class named Employee, with private fields for name,age and Employee Id. We cannot access these fields from outside the class , but we can accessing these private fields Through properties.

Why We use properties
Marking the class field public & exposing is a risky, as you will not have control what gets assigned & returned.

To understand this clearly with an example lets take a student class who have ID, pass mark , name.Now in this example some problem with public field

1. ID should not be -ve.
2. Name can not be set to null
3. Pass mark should be read only.
4. If student name is missing No Name should be return.

To remove this problem We use Get and set method.

// A simple example

public class student

{

public int ID;

public int passmark;

public string name;

public class programme

{

    public static void main()

    {

       student s1 = new student();

       s1.ID = -101; // here ID can't be -ve

       s1.Name = null ; // here Name can't be null

    }

}

Now we take an example of get and set method

public class student

{

    private int _ID;

    private int _passmark;

    private string_name ;

    // for id property

   public void SetID(int ID)

   {

       if(ID<=0)

       {

         throw new exception("student ID should be greater then 0");

       }

       this._ID = ID;

    }

    public int getID()

    {

       return_ID;

     }

   }

   public class programme

   {

       public static void main()

       {

         student s1 = new student ();

         s1.SetID(101);

      }

      // Like this we also can use for Name property

      public void SetName(string Name)

      {

        if(string.IsNullOrEmpty(Name))

        {

          throw new exeception("name can not be null");

        }

        this._Name = Name;

     }

     public string GetName()

     {

        if( string.IsNullOrEmpty(This.Name))

        {

          return "No Name";

       }

       else

      {

        return this._name;

      }

      // Like this we also can use for Passmark property

      public int Getpassmark()

      {

        return this._passmark;

      }

}                                                                                                                                             Previous....
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Exception Handling in C#

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An exception is an error Which occurs during a program is running. 

C# exception handling has four keywords: try, catch, finally and throw.

Try: A try block identifies a block of code for which particular exceptions will be activated. It's followed by one or more catch blocks.

catch: A program catches an exception with an exception handler at the place in a program where you want to handle the problem. The catch keyword indicates the catching of an exception.

finally: The finally block is used to execute a given set of statements, whether an exception is thrown or not thrown. For example, if you open a file, it must be closed whether an exception is raised or not.

throw: A program throws an exception when a problem shows up. This is done using a throw keyword.

Syntax

try
{
   // a statements 
}
catch( Exception e1 )
{
   // error handling code
}

finally
{
   // statements to be executed
}

     This article talks about best practices of exception handling, and guides you for some common programming mistakes developers do, as that seems appropriate in most applications written.

Best practices are only guidelines and do not enforce you to follow these, but if followed correctly then you won't only write less lines of code, but you work and code with more logical approach of coding and designing the code modules.

#1 Do Not Throw Exceptions to Control Application Flow

Scenario

The following code throws an exception inappropriately, when a supplied product is not found

.
public static void CheckProductExists(int ProductId)
{
    //... search for Product    if (ProductId == 0) // no record found throw error    {
        throw (new Exception("Product is  Not found in inventory"));
    }
    else    {
        Console.WriteLine("Product is available");
    }
}
static void Main(string[] args)
{   
     Console.WriteLine("Enter a ProductId you would like to search [1 – 100]");      

 int productId = Int32.Parse(Console.ReadLine());
 
      CheckProductExists(productId);
      Console.ReadLine();
}
After execution of Main, and when 0 is passed as shown in Figure 1-1 below.

 Figure 1-1 Reading productId from Console

The value being passed to the program as shown in Figure 1-1 will result in an exception as shown in Figure 1-2 below.

Problem

Throwing an exception as shown in Scenario section and Figures 1-1 and 1-2 is expensive; presumably throwing an exception causes the CPU to fetch code and data it would otherwise not have executed. You probably should not throw any exceptions in that scenario.

Solution

Consider the possibility that the code shown above not finding a product is an expected condition. Hence, re-factor the code to return a value that indicates the search result after the method's execution. The following code re-writes the code to verify the availability of the product in inventory and sets a flag to true or false. 

This apparently avoids a new exception being thrown. The calling code uses a flag value to identify whether the inventory has the specified product or not.

public static bool CheckProductExists(int productId)
{
    //... search for Product    if (productId == 0) // no record found    {
        return false;
    }
    else    {
        return true;
    }
}

static void Main(string[] args)
{
    Console.Write("Enter a ProductId you would like to search [1 – 100] : "); 
    int productId = Int32.Parse(Console.ReadLine());

    if (!CheckProductExists(productId) == false)
    {
        Console.WriteLine("Found");

    }
    else

    {

         Console.WriteLine("Not Available");
    }
    Console.ReadLine();}


#2 Use Validation Code to Reduce Unnecessary Exceptions
Scenario

Using a try/catch block can be a very handy solution for most programming situations, for example the most commonly known is DivideByZero. The following code uses a try/catch block to handle DivideByZero and that is pretty convincing.

static void Main(string[] args)

{
    Console.Write("Enter numerator : "); 
    int numerator = Int32.Parse(Console.ReadLine());

    Console.Write("Enter divisor : ");
    int divisor = Int32.Parse(Console.ReadLine());

    try    {
        double result = numerator / divisor;
        Console.WriteLine(result);
    }
    catch (DivideByZeroException ex)
    {
        Console.WriteLine(ex.Message);
    }
    
    Console.ReadLine();
}

Problem

There is no need to perform exception handling if we can use the basic validation techniques before code is executed. In this scenario an exception only needs to be handled if the divisor is 0 (zero) otherwise it should work fine.

Solution

Let's re-factor the code and rewrite it so try/catch blocks can be avoided, and as a result is more efficient.
 

static void Main(string[] args)

{

    Console.Write("Enter nemerator : ");

    int numerator = Int32.Parse(Console.ReadLine());

    Console.Write("Enter divisor : ");

    int divisor = Int32.Parse(Console.ReadLine());

    if (divisor != 0)

    {

        Console.WriteLine(numerator / divisor);

    }

    else

    {

        Console.WriteLine(Double.NaN);

    }

   

    Console.ReadLine();

}

Figure 1-4 Using validation code instead to avoid try/catch to handle an exception

                                                                                                    

                                                                                                                                                                                           Previous....

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Struct in C#

                                                                                                                                Previous....

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In C#, a structure is a value type data type. so it is stored in stack and it use enum,delegate and there may be constructor or not. The struct keyword is used for creating a structure.

Defining a Structure

structure is a homogeneous datatype means there can be more then one datatype. 

For example, here is the way you would declare the Book structure:

struct student
{
   public string name;
   public int class ;
   public string subject;
   public int id;
};  

The following program shows the use of the structure:

using System;
     
struct student
{
   public string name;
   public string aclass;
   public string subject;
   public int id;
};  

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

     student student1;       
     student student2;       

      /* student1 detail */
      student1.name = "munesh";
      student1.class = "VI"; 
      student1.subject = "DOT Net programming";
      student1.id = 16;

      /* student 2 detail */
      student2.name = "rahul";
      student2.class = "VII";
      student2.subject =  "C programming";
      student2.id = 20;

      /* print student1 info */
      Console.WriteLine( "student 1 name : {0}", student1.name);
      Console.WriteLine("student1 class : {0}", student1.class);
      Console.WriteLine("student 1 subject : {0}", student1.subject);
      Console.WriteLine("student 1 Id :{0}", student1.id);

      /* print Book2 info */
      Console.WriteLine("student2 name : {0}", student2.name);
      Console.WriteLine("student 2 class : {0}", student2.class);
      Console.WriteLine("student2 subject : {0}", student2.subject);
      Console.WriteLine("student 2 id : {0}", student2.id);       

      Console.Readline();

   }
}

When the above code is compiled and executed, it produces the following result:

student 1 name : munesh
student 1 class : VI
student 1 subject : Dot Net Programming
student 1 id : 16
student 2 name : Rahul
student 2 class : VII
student 2 subject : C programming
student 2 id : 20

Class vs Structure go to this link

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