Database Programming

All of them (as well as other bases) are based on the place-value system: in decimal, each digit has a place-value that is 10 times as much as the digit to the right. In base 2, and base 16, the factors 2 and 16, respectively, are used instead. Base 2 needs 2 different symbols (0 and 1) to represent each digit; base 10 needs 10 symbols (0-9), and base 16 needs 16 different symbols. For this purpose, apart from the digits 0-9, the letters A-F are also used as "digits", where A means 10, B means 11, etc.

In a standard queue data structure re-buffering problem occurs for each dequeue operation. To solve this problem by joining the front and rear ends of a queue to make the queue as a circular queue

Circular queue is a linear data structure. It follows FIFO principle.

• In circular queue the last node is connected back to the first node to make a circle.
• Circular linked list fallow the First In First Out principle
• Elements are added at the rear end and the elements are deleted at front end of the queue
• Both the front and the rear pointers points to the beginning of the array.
• It is also called as "Ring buffer".
• Items can inserted and deleted from a queue in O(1) time.

Circular Queue can be created in three ways they are

· Using single linked list

· Using double linked list

· Using arrays

Using single linked list:

It is an extension for the basic single linked list. In circular linked list Instead of storing a Null value in the last node of a single linked list, store the address of the 1st node (root) forms a circular linked list. Using circular linked list it is possible to directly traverse to the first node after reaching the last node.

The following figure shows circular single linked list:

Using double linked list

In double linked list the right side pointer points to the next node address or the address of first node and left side pointer points to the previous node address or the address of last node of a list. Hence the above list is known as circular double linked list.

The following figure shows Circular Double linked list :-

Algorithm for creating circular linked list :-

Step 1) start

Step 2) create anode with the following fields to store information and the address of the next node.

Structure node

begin

int info

pointer to structure node called next

end

Step 3) create a class called clist with the member variables of pointer to structure nodes called root, prev, next and the member functions create ( ) to create the circular linked list and display ( ) to display the circular linked list.

Step 4) create an object called 'C' of clist type

Step 5) call C. create ( ) member function

Step 6) call C. display ( ) member function

Step 7) stop

Algorithm for create ( ) function:-

Step 1) allocate the memory for newnode

newnode = new (node )

Step 2) newnode->next=newnode. // circular

Step 3) Repeat the steps from 4 to 5 until choice = 'n'

Step 4) if (root=NULL)

root = prev=newnode // prev is a running pointer which points last node of a list

else

newnode->next = root

prev->next = newnode

prev = newnode

Step 5) Read the choice

Step 6) return

Algorithm for display ( ) function :-

Step 1) start

Step 2) declare a variable of pointer to structure node called temp, assign root to temp

temp = root

Step 3) display temp->info

Step 4) temp = temp->next

Step 5) repeat the steps 6 until temp = root

Step 6) display temp info

Step 7) temp=temp->next

Step 8) return

Using array

In arrays the range of a subscript is 0 to n-1 where n is the maximum size. To make the array as a circular array by making the subscript 0 as the next address of the subscript n-1 by using the formula subscript = (subscript +1) % maximum size. In circular queue the front and rear pointer are updated by using the above formula.

The following figure shows circular array:

Algorithm for Enqueue operation using array

Step 1. start

Step 2. if (front == (rear+1)%max)

Print error "circular queue overflow "

Step 3. else

{ rear = (rear+1)%max

Q[rear] = element;

If (front == -1 ) f = 0;

}

Step 4. stop

Algorithm for Dequeue operation using array

Step 1. start

Step 2. if ((front == rear) && (rear == -1))

Print error "circular queue underflow "

Step 3. else

{ element = Q[front]

If (front == rear) front=rear = -1

Else

Front = (front + 1) % max

}

Step 4. stop

according to definitions on secdatabase.com, here is difference:

Form S-8 is the Registration Statement under the Securities Exchange Act of 1933. It is used by a publically traded company to register securities that will be offered to its employees via benefit or incentive plans.

Form 8-K is the report of unscheduled material events or corporate changes at a company that could be of importance to the shareholders or the Securities and Exchange Commission.

Advantages of data flow diagram:

· A simple graphical technique which is easy to understand.

· It helps in defining the boundaries of the system.

· It is useful for communicating current system knowledge to the users.

· It is used as the part of system documentation file.

· It explains the logic behind the data flow within the system.

Disadvantages of data flow diagram:

· Data flow diagram undergoes lot of alteration before going to users, so makes the process little slow.

· Physical consideration are left out.

· It make the programmers little confusing towards the system.

· Different DFD models have different symbols like in Gane and Sarson process is represented as rectangle where as in DeMarco and Yourdan symbol it is represented as eclipse.