Add New Elements or Content in jQuery

JQuery provides some standard functions through which developer can easily add element/content to an existing element. User can add an element after or before an existing element by using jQuery functions. These element can also be added using callback functions. Just check some value and according to condition, we can add element easily.

Following are jQuery methods that are used to add new content:

Append method

This function insert content or new element at the end of selected html element. For example

$("#lblComment").append("last comments");

This function will add specified text after the existing text of selected label.

prepend()

This function insert content or new element at the beginning of selected html element. For example

$("#lblComment").prepend("start comments");

This function will add specified text before the existing text of selected label. We can use both these methods to add multiple content by using multiple parameters. These functions can easily get multiple parameters as shown below:

$("#lblComment").prepend("one", "two", "three");
$("#lblComment").append("eight", "nine", "ten");

After() and before()

After method inserts content after the selected html element and before method inserts content before the selected html element. More can be explained by following jQuery code fragment:

$("#lblComment").after("after adding text");
$("#lblComment").before("before adding text");

Both these functions will add the specified text after and before the selected label element respectively. Same as append and prepend, these functions can also be used for adding multiple elements to an existing.

In above examples, we have added only texts only but we can add any other element in place of that text. Just write the element’s html code and place as parameter of these functions, that element will add easily. In further article we will remove the added element/content and how to use/append css classes through jQuery code fragment.

Data Definition Language (DDL) Triggers in SQL

A DDL trigger is fired in response to DDL statements, such as CREATE TABLE or ALTER TABLE. DDL triggers can be used to perform administrative tasks, such as database auditing.

Database auditing helps in monitoring the DDL operations on a database. DDL operation can include operations such as creation of a table or view, or modifications of a table or procedure. Consider an example, where you want the database administrator to be notified whenever a table is created in the Master Database. For this purpose, you can create a DDL trigger.

Depending on the way in which triggers are fired, they are categorized as:

After Triggers

The after trigger can be created on any table for the insert, update or delete operation just like other triggers. The main difference in the functionality of an after trigger is that it is fired after the execution of the DML operation for which it has been defined. The after trigger is executed when all the constraints and triggers defined on the table are successfully executed.

By default, if more than one after trigger is created on a table is for a DML operation such as insert, update, or delete, then the sequence of execution is the order in which they were created.
For example, the EmpSalary table stores the salary and tax details for all the employees in an organization. You need to ensure that after the salary details of an employee are updated in the EmpSalary table, the tax details are also recalculated and updated. In such a scenario, you can implement an after trigger to update the tax details when the salary details are updated.

Instead of Triggers

The instead of triggers can be primarily used to perform an action, such as a DML operation on another table or view. This type of trigger can be created on both a table as well as a view.

An instead of trigger can be used for the following actions:

• Ignoring parts of a batch.
• Not processing a part of a batch and logging the problem rows.
• Taking an alternative action when an error condition is encountered.

For example, if a view is created with multiple columns from two or more tables, then an insert operation on the view is only possible if the primary key fields from all the base tables are used in the query. Alternatively, if you use an instead of trigger, you can insert data in the base tables individually. This makes the view logically updateable.

You can even create an Instead of trigger to restrict deletion in a master table. For example, you can display a message “Master record cannot be deleted” if a delete statement is executed on the Employee table of the AdventureWorks database.

Unlike after triggers, you cannot, create more than one Instead of trigger for a DML operation on the same table or view.

Nested Triggers

Nested triggers are fired due to actions of other triggers. For example, you delete a row from TableA. A trigger on TableA deletes rows from TableB. Because you are deleting rows from TableB, a trigger is executed on TableB to record the deleted rows.

Recursive Triggers

Recursive triggers are a special case of nested triggers. Unlike nested triggers, support for recursive triggers is at the database level. As the name implies, a recursive trigger eventually calls itself. There are two types of recursive triggers, Direct and Indirect.

Direct Recursive Trigger

A direct trigger is a trigger that performs the same operation (insert, update, or delete) on the same table causing the trigger to fire itself again.

Indirect Recursive Trigger

An indirect trigger is a trigger that fires a trigger on another table and eventually the nested trigger ends up firing the first trigger again. For instance, an UPDATE on TableA fires a trigger that in turn fires an update on TableB. The update on TableB fires another trigger that performs an update on TableC. TableC has a trigger that causes an update on TableA again. The update trigger of TableA is fired again.

Implementing Callback Functions in JQuery

Callback function reference will execute after the current effect/function/event finished completely. This type of function can be used after any event completion like to set an element’s value after execution of some function finished.

In earlier article we have discussed about callback function execution after finishing effect. These functions executes after current effect have been finished. As the effect completed, the function reference specified as callback will be executed.

Following code block will change the text field of element having id "testComment" as mentioned in the code. This whole process will take place after button (btnComment) click event done.

$("#btnChange").click(function(){
  $("#testComment").text(function(i,origText){
    return "Old text: " + origText + " New text: Changed! on index: " + i;
  });
});

A callback function is one which is passed as an argument in another function and which is invoked after some kind of event. The call back nature of the argument is that, once its parent method completes, the function which this argument represents is then called; that is to say that the parent method calls back and executes the method provided as an argument.

So we can perform anything after any event or any ajax request also e.g. we want to change the html of a div element after clicking on a button, the following code fragment helps us:

$("#btnChange").click(function(){
  $("#testDiv").html(function(i,origText){
    return "Old html: " + origText + " New html: This is new HTML for this div element";
  });
});

Callbacks are so-called due to their usage with pointer languages. If you don't use one of those, just understand that it is just a name to describe a method that's supplied as an argument to other method, such that when the first method is called and its method body completes, the callback method is then invoked, or in other words "called at the back" of the other function.

Implementation of pointer variable in Data Structures through C Language

            Implementation of pointer variable with example

Pointer Operations

One can do only possible two operations on pointers One is assignment and another one is simple addition or subtraction of values with pointer variables. No other operation is permitted to perform on the pointer variables because they simply contain the memory addresses or locations not the variables.

Assignment operation:

      The assignment operation is nothing but assigning a pointer variable with the memory address. The memory address must be known (static or dynamic). A pointer can be assigned with the address stored in another pointer variable. To perform assignment operation the two “pointer variables” must be of the same type. The pointer must point to memory locations that contain the similar type values like integers, floating-point number, characters etc. If ‘a’ is an integer variable then the address of ‘a’ can be assigned to any pointer variable of the type integer.

Example:
Void main()
{
Int*p, a=120;
 /* p is a pointer variable, a is a simple variable*/
Printf(“Address = %Id, Value = %d\n”,&a,a);
P = &a;
/*p is assigned with address of a */
Printf(“Address = %Id, Value = %d”,p*p);
/*Both of the above printf statements Display the same values*/

In the above example, the pointer variable is assigned with the memory address that is already allocated by the system to other variable. In this type of simple assignment  the address of variable ‘a’ is stored in pointer p. You can also note that the data type of both the variables, ‘a’ and ‘b’ is similar i.e. ‘int’.

       If the pointer variable is used to change the value at the memory location, then it automatically changes the value of the non-pointer variable ‘a’. This is the concept that comes into picture when ‘call-by-reference’ is used (i.e. when the formal parameters are pointer types)
Example:
Main()
{
Int *p,a=10;
Printf(“Value of a, before pointer operation: %d”,a);
/*10*/
P=&a;
*p=26;
Printf(“Value of a, after pointer operation: %d”,a);
/*26*/
}
In the example the address of a variable (a) is assigned to a pointer variable (p). When the content of memory is changed by the pointer variable it affects the original variable. It is mainly because both the variables refer the same memory location or address.
Example to show the effect of ‘call-by-reference’:
Void fun (int a, int *b)
/*a is a value parameter, b is a reference parameter*/.
{
a++;
/*’a’ local variable of fun() incremented by 1*/
*b = *b + a; /* pointer ‘b’ points to the memory location of variable ‘b’ of main()*/
}
main()
{
Int a=10, b=12;
Printf(“a=%d, b=%d\n”,a,b);
fun(a,&b);
printf(“a=%d,b=%d”,a,b);

}

 

The parameter ‘b’ of function fun() is a pointer. So, it changes the value of variable ‘b’ of main(). Both refer to same memory.
Example:
Main()
{
Int *p1, *p2, a=10;
Printf(“a=%d\n”,a);          /*a=10 is displayed*/
p1=&a;    /*pointer p1 is assigned with address of variable ‘a’*/
p2=p1;    /*pointer p2 is assigned with value of p1 (address of a). another way of assignement */
printf(“Value at p1=%d\n”,*p1);     /* 10 is displayed */
printf(“Value at p2=%d\n”,*p2);      /* 10 is displayed */
}
The above example is self-explaining via comments. You can mainly note that the non-pointer variable ‘a’, pointer p1 and p2 are of same type (int). Now let us see an example of dynamic memory allocation:
Main()
{
Int*p;
p=(int*) malloc(sizeof(int)); *p=10; printf(“%d”,*p);
}
In this example the pointer variable p is assigned with the address that is returned from the malloc(). An example of assigning dynamically allocated memory. The dynamically allocated memory  stores integer and the pointer is also of the type integer.

Some operations are

• Addition and Subtraction operation:
• C program to read and print a dynamic array of the user required size
• C Program to implement simple searching using dynamic array
• C Program to count the frequency of a number in a dynamic array.
• C program to find the number of prime numbers stored in a dynamic array.

Pointer and Dynamic memory Allocation in data structure through C Language

                                                            When the variables are declared in a program, usually the memory is allocated during the compilation that is statically. The memory referred by such variables is used to store the value (data) directly. Instead of data directly if another memory location is to be stored in the variables, then it should be a pointer variable. As we are already familiar with the dynamic memory allocation, and if it is to be implemented then without pointer variables it is not possible. During the execution of program dynamic memory is allocated, so there must be a variable that stores addresses of memory at that time. That is the reason why pointer variable is used. When pointer variables are declared no memory is allocated to store the data. The memory is allocated to them only to store the memory address not the data. Taking this as an advantage the pointer variable can be made to point dynamically allocated memory location.

For example if “p” is a pointer variable declared of the type “int” then for p memory is allocated to store the address of a memory is location that stores an “int” (integer data). Here the memory address that is to be stored in pointer variable may be static or dynamic. Usually it is to be dynamic memory allocation. It can be pictured as follows:
int *p, a;           ‘p’ is a pointer variable, ‘a’ is a simple integer variable. For ‘a’
                           memory is allocated statically to store integer data. Of course for                  
                           ‘p’ also memory is allocated but to store an address not data.
a=10;                 at memory location is reserved by ‘a’, an integer 10 is stored.
P=&a;                ‘p’ as it is pointer variable used to store address of statically
                           allocated memory.
With the help of pointer ‘p’ is possible to refer integer value stored at variable ‘a’ indirectly through pointer ’p’.

If ‘a’ is user to print, it prints the value 10, if &a (&a is called address operator) is used, it prints 1000 as per the examples. If p is used it also prints 1000 the content of p the address of memory is allocated to a. If *p (de-referencing of pointer) is used it prints the value of memory location pointed by the pointer variable. Here it prints the value of ‘a’ that is 10.
We can take the advantage of storing the memory address by a pointer variable during the execution of program. So instead of storing the already allocated static memory, a dynamic memory maybe requested during the execution of program and the dynamically allocated memory address may be stored in a pointer variable and it is used as it is normal variable.
Dynamically the memory is allocated using the standard functions calls depending on the high level languages used. Like in Pascal new used, in C++ new operator is used and in C language the functions like malloc(), calloc() and realloc() are used.
So, in C language if memory is requested by the user during the execution of the program to store data one of the following functions may be used. The functions are different as per the purpose and the numbers of arguments passed to the functions. All these functions return an address called the base address of dynamically allocated memory and is store in a pointer variable.

For example (int *) malloc (20) – allocates 20 bytes of consecutive memory dynamically on success, (or return a NULL address if not successfully allocates) and returns the base address. The returned address may be stored in a pointer variable of the type int and 10 integers can be referred with the help of that pointer variable. It is nothing but an array of size 10 for which the memory is allocated during the execution of program. The initial values stored in the memory location allocated are garbage values.

So, the memory allocated by the ‘calloc’ function is the product of number_of_elements and size_of_each_element. For example (int *) calloc (10, 2) allocates 20 bytes of dynamic memory. So, 10 integers can be stored in those memory locations. The initial values of these memory locations will be zero. Similar to malloc (), the returned address may be stored in a pointer variable and treated as an array of 10 integers.

If the dynamic memory allocated using either calloc or malloc is to be changed during the execution of program then realloc is used. It allocates completely a new memory block and copies the contents of already allocated block and returns the new base address. That address may be stored in the same pointer variable. Otherwise it expands the existing block and returns the same base address. The change may even reduce the size of already allocated block.
The dynamic memory is allocated from the heap area of main memory. If the requested memory is not available the dynamic memory is allocation functions return NULL address or invalid address, it is also treated as a 0 (zero) value. The dynamically allocated memory may be freed from the programmer after his/her usage using free () function. The prototype of void free (void *block) is available in alloc.h. If the user does not free the dynamically allocated memory, it is the function of operating system to collect the dynamic memory periodically and give it back to heap. This function of operating system called as “garbage collection”. It is better practice for the programmers to free the dynamically allocated memory after the use of such memory. If you write the statements for dynamic memory allocation then remember that the free statement is also used in the program before the end of program to ensure to free the dynamically allocated memory. 

How to Validate DropDownList in ASP.NET

Introduction

Various methods is available to validate the TextBox but very few methods is available to validate the Dropdownlist. Here i have two methods to validate it. In the first method i will use RequiredFieldValidator control with InitialValue property, in the second method i will use javaScript. for validation.

I-Method

In the first method, first to add some items in the dropdownlist. Now, take a RequiredFieldValidator control to validate the Dropdownlist. Set some required properties of validator control. These are:

ControlToValidate="Id of Dropdownlist control"
ErrorMessage=" Please select item from Dropdownlist "
InitialValue = "Match with Text item which is available in Dropdownlist also you do not want to display. Like

<asp:ListItem>select one</asp:ListItem>
            <asp:ListItem>Apple </asp:ListItem>
            <asp:ListItem>Mango</asp:ListItem>
            <asp:ListItem>Orange</asp:ListItem>

Here, i set the InitialValue = select one.

Complete code to describe more:

<%@ Page Language="C#" %>

<!DOCTYPE html>

<script runat="server">

    protected void Button1_Click(object sender, EventArgs e)
    {
        Label1.Text += "Your selected item is <br/>"+DropDownList1.SelectedItem.Text;
    }

    protected void Page_Load(object sender, EventArgs e)
    {
   
    }
</script>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:DropDownList ID="DropDownList1" runat="server" Height="30px" Width="149px" AutoPostBack="True">
            <asp:ListItem Selected="True">select one</asp:ListItem>
            <asp:ListItem>Apple </asp:ListItem>
            <asp:ListItem>Mango</asp:ListItem>
            <asp:ListItem>Orange</asp:ListItem>
        </asp:DropDownList>
        <br />
    </div>
        <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="DropDownList1" ErrorMessage="RequiredFieldValidator" InitialValue="select one">Please Select Item</asp:RequiredFieldValidator>
        <asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Button" />
        <br />
        <asp:Label ID="Label1" runat="server"></asp:Label>
    </form>
</body>
</html>

Output

II-Method

In the second method we use javascript to validate the Dropdownlist. First to add some Text and Value in the control, Now With the help of getElementById property we can access the value of this control. Generate error message with the help of alert dialog box when accessed value is match with selected value of this control.

Complete code:

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default5.aspx.cs" Inherits="Default5" %>

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
    <script>
   function validate()
   {
       var req = document.getElementById('<%=DropDownList1.ClientID %>');
       if(req.value=="0")
       {
           alert("please select one item");
       }
    }
   </script>
</head>
<body>
    <form id="form1" runat="server">
 
        <asp:DropDownList ID="DropDownList1" runat="server">
            <asp:ListItem Value="0" Text ="Select"></asp:ListItem>
            <asp:ListItem Value="1" Text ="Education"></asp:ListItem>
            <asp:ListItem Value="2" Text ="Technology"></asp:ListItem>
            <asp:ListItem Value="3" Text ="Entertainment"></asp:ListItem>
        </asp:DropDownList>
       
   
   
        <p>
            <asp:Button ID="Button1" runat="server" style="height: 26px" Text="Button" OnClientClick="validate()" />
        </p>
   
    </form>
</body>
</html>

Download : Complete Code

String Literals and Constants in C Language

There is no separate data type for strings in C language. In C language, a string is an array of characters and terminated by NULL character which is denoted by the escape sequence '0'. A NULL terminated string is the only type string defined using C language.

A string is stored as a sequence of characters in an array terminated by \0. For example, consider the string "DOTPROGRAMMING". This string is stored in the form of an array as shown below:

Note that the characters are stored from location zero. Each location holds one character string from 0 to 14. The string always ends with NULL. Character denoted by '\0'. Here, the string "DOTPROGRAMING" is called a string literal.

String Literal or Constant

A string literal or constant is a sequence of characters enclosed within double quotes. For example, "DOT PROGRAMMING", "DOT", "PROGRAMMING" are all string literals. When a string literal is defined, the C compiler does the following activities:

• The compiler creates an array of characters.
• Initializes each location of array with the characters specified within double quotes in sequence.
• Null-terminates the string that is appends ‘\0’ at the end of the string. This is done by the compiler automatically.
• Stores the starting address of the string constant that can be used later. For example, the literals "DOT", and "PROGRAM" can be stored in the memory as shown below:

Referencing String Literal or Constant

An array of integers is stored in contiguous memory locations, it is clear from the above figures that a string literal is also stored in memory contiguously one after the other. So, each character of the literal or constant can be accessed using index (array or pointer concept can be used). For example, consider the following program:

main()
{
clrscr();
printf("5c","DOT"[0]);
printf("5c","DOT"[1]);
printf("5c","DOT"[2]);
getch();
 }

The entire string can be referred and display as shown below:

main()
{
clrscr();
printf("DOT");
getch();
 }

Each of the above program will outputs "DOT" string on the monitor or any output device connected with the PC.