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Wednesday, January 28, 2015
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QUEUE in C Language

12:11 AMWednesday, January 28, 2015
  • It’s special data structure based on FIFO (First In First out Concept).
  • It can be implemented using One dimensional Array as well as Singly linked list.
  • REAR and FRONT are the two external pointers holds the addresses of two ends respectively.
  • Insertion and deletion are done from two different ends known as REAR and FRONT respectively.  

 Types of Queue:

  • Linear Queue: Elements are arranged in a linear order.
  • Circular Queue: Elements are arranged in a queue by means of circular array.
  • D-Queue.( Double Ended QUEUE ) The ADD and DELETE operations are done from both the ends.
  • Priority QUEUE: The elements are stored and deleted in QUEUE on this basis of Priority.
QUEUE in C programming

Linear Queue:

Algorithm using Linked List:
CREATELQ( ARR, N , FRONT , REAR, ITEM)
[ ARR is the name of the array of size N. ITEM is the info. of element inserted in queue]
If REAR = N Then:
Write: ‘ Overflow’
Exit
[ End of If ]
If REAR = 0 Then:
FRONT <-- 1
REAR <-- 1
Else: 
REAR <-- REAR + 1
[ End of If]
ARR[REAR] <--  ITEM
Exit

Algorithm for DELETE operation in Linear Queue:

DELETELQ ( ARR, FRONT, REAR)
[ ARR is name of the array of size N]
If   FRONT=NULL Then:
    Write: ‘ Empty Queue’
    Exit
[ End of If ]
ITEM <-- FRONT --> INFO
If REAR = FRONT Then:
    REAR <-- NULL
    FRONT <-- NULL
Else
    FRONT <-- FRONT --> NEXT
[ End of If]
Write: ‘Deleted Element ‘, ITEM
END

Algorithm using  One dimensional Array.

ADDLQ(QUEUE,N, ITEM, REAR, FRONT)
If REAR=N Then:
   Write: ‘ OverFlow’
   Exit
[ End of If]
If REAR = -1 Then:
   REAR <-- 0
   FRONT <-- 0
Else
   REAR <-- REAR +1
[ End of If]
QUEUE[ REAR] <-- ITEM
END

DELETELQ(QUEUE , REAR, FRONT)
If FRONT =-1 Then:
    Write: ‘ Empty Queue’
    Exit
[ End of If ]
Write: ‘ Deleted Element’ FRONT --> INFO
If FRONT= REAR Then:
    FRONT= -1
    REAR= -1
Else
   FRONT <-- FRONT --> NEXT
[ End of If]
End

Circular Queue:

ADDCQ(QUEUE,N, ITEM, REAR, FRONT)
If FRONT =REAR +1REAR=N Then:
   Write: ‘ OverFlow’
   Exit
[ End of If]
If REAR = -1 Then:
   REAR <-- 0
   FRONT <-- 0
Else
   REAR <-- REAR +1
[ End of If]
QUEUE[ REAR] <-- ITEM
END
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