In this video we will create a simple abstract data type, list. We will define its properties and operations that can be performed on a list. We will not implement list in an programming language in this video. That we will see in upcoming videos of Data Structure using C. After defining the properties of the list Dr. Yogendra Pal listed some operations like PRINTLIST, END, FIRST, NEXT, PREVIOUS, INSERT, LOCATE, RETRIEVE, DELETE and MAKENULL. We will implement these operations using c programming in upcoming videos. Complete Data Structure videos can be found here: https://goo.gl/HX72pI Join Data Structure using C online course: https://goo.gl/I1ZHK3 Learn By Watch is a YouTube channel where we teach various subjects in Hindi. You can watch and subscribe our YouTube channel from here: https://goo.gl/JT9uzi

1. Abstract Data Types:
Lists

2. List
• A List is a sequence of zero or
more elements.
a1, a2, a3, a4, ………..,an
Where n  0,
a1 is the first element
an is the last element
n is length of the list
if n = 0, the list is empty (no
element)
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3. More about lists
• Elements are linearly ordered.
ai precedes ai+1
for i = 1, 2, 3,… (n-1)
ai follows ai-1
for i = 2, 3,… n
• Element ai is at position i
a1, a2, a3, a4, ………..,an
Not a list
a1, a3, a5, a7, ………..,an
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1 2 3 4 n Position of
element.

4. More about lists
a1, a2, a3, a4, a5
a1, a2, a3, a4, a5, a6, a7
a1, a2, a3, a4
a1, a2, a3
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5. LIST: Abstract Data Type
• L: List of elements
• e: an element
• p: position
LIST ADT
Properties
- Sequence of linearly
ordered elements.
Operations
• Insert(e, p, L)
• Locate(e,L)
• Retrieve(p,L)
• Delete(p,L)
• Next(p,L)
• Previous(p,L)
• MakeNull(L)
• First(L)
• PrintList(L)
• END(L)
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6. Print all elements of the LIST ADT
• PRINTLIST(L)
• Print the elements of L in order of occurrence.
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7. End of list
a1, a2, a3, a4 ,…………, an
• END(L)
• Returns the position following an on the list.
a1, a2, a3, a4, a5, a6, a7
• END(L) will return 8 for this list
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1 2 3 4 7 Position of element.

8. First position on LIST ADT
a1, a2, a3, a4 ,…………, an
• FIRST(L)
• Returns the first position on the list.
• If L is empty the position returned is END(L)
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1 2 3 4 n Position of element.

9. Next and Previous position on LIST ADT
• NEXT(p, L)
• Returns the position following the position p on the list.
• PREVIOUS(p, L)
• Returns the position preceding the position p on the list.
• If p is the last position on the list then NEXT(p,L) will return END(L).
• PREVIOUS is undefined if p is 1.
• Both functions are undefined if L has no position p.
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10. Insert an element in LIST ADT
a1, a2, a3, a4, a5, a6, a7
• INSERT(e, p, L)
a1, a2, a3, a4 ,……ap ,…… an
a1, a2, a3, a4 ,……,ap-1, e, ap ,…… an
• INSERT(3, 5, a1, a2, a3, a4, a5, a6, a7)
a1, a2, a3, a4, a5, a6, a7
a1, a2, a3, a4, 3, a5, a6, a7
• if p = END(L) then L becomes a1, a2, a3, a4, a5, a6, a7, e
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11. Locate an element in LIST ADT
33, 90, 76, 21, 65, 36, 87
• LOCATE(e, L)
• Returns the position of e on list L
• LOCATE(76,L)
• Return 3
• If e appears more than once, then the position of first occurrence is
returned.
• If e does not appear than END(L) is returned.
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1 2 3 4 7 Position of element.

12. Retrieve an element from LIST ADT
33, 90, 76, 21, 65, 36, 87
• Retrieve(p, L)
• Returns the element at position p from the List.
• Retrieve(3, L) will return 76
• The result is undefined if p = END(L) or if L has no position p
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1 2 3 4 7 Position of element.

13. Delete an element from the list
a1, a2, a3, a4, a5, a6, a7
• DELETE(p, L)
a1, a2, a3, a4 ,……ap ,…… an
a1, a2, a3, a4 ,……,ap-1, ap+1 ,…… an
• DELETE(5, L)
a1, a2, a3, a4, a5, a6, a7
a1, a2, a3, a4, a6, a7
• Result is undefined if L has no position p
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14. Empty entire LIST ADT
• MAKENULL(L)
• L becomes empty and returns position END(L)
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