List and Pointers Lesson

7/31/2019 List and Pointers Lesson

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List and Pointers



• Programming languages can distinguish between different data

types such as:

– Integers

– Real numbers

–

Strings• They also provide data structures such as:

– Arrays

– Records

• OOPs have classes which are user-defined datatypes.

Introduction



• Real-life problems require other structures to store data items called

lists.

• A list that you might use in real life would be a shopping list.

• To define a list, we are going to view it as an abstract data type.

– A data type whose properties are specified independently of anyparticular programming language.

Introduction



• Linear lists

– Elements are stored in adjacent locations in memory

– The compiler reserves the space for the array when it is declared

– Therefore there is no way to increase or decrease the size of the array

in memory

• Linked lists

– Allocates memory space only during runtime, meaning that it is memory

efficient;

–

Elements are known as nodes. – Each element of the list has an extra data field called a pointer that links

to the next node in the list.

Implementation



•Operations that need to be performed on a list are: – Initialising the list

• Declare the array and initialise variable NumberOfElements

• Declare the record and initialise start node

– Inserting an element

• Stores the element in the next available space, then increment

NumberOfElements • Store new node directly after start node

– Deleting an element

• Find element to be deleted and move subsequent elements up a space, then

decrement NumberOfElements

– Finding an element

• Use linear search

– Getting the length of the list

• Output NumberOfElements

– Displaying the entire list

• Starting from the first element in the array, output each element until the end

of the array is reached

Introduction



Linked lists

• Elements are known as nodes.

• In linked lists, elements do not have to be stored adjacently in memory.

• Each element of the list has an extra data field called a pointer that links to

the next node in the list.



A node

Data fieldPointer

Bananas 21

Node address



Inserting a node

Bananas 21

Start node

Carrots •2Start 1

Pears •4 2

NumberOfElements



Inserting a node

Bananas 21 Carrots •2Start 4

Pears •4 2

NumberOfElements



Inserting a node

Bananas 21 Carrots •2Start 4

Pears 14 2

NumberOfElements



Inserting a node

Bananas 21

Carrots •2

Start 4 Pears 14

3

NumberOfElements



Deleting a node

Bananas 21

Carrots •2

Start 4 Pears 14

3

NumberOfElements



Deleting a node

Bananas 21

Carrots •2

Start 1 Pears 14

3

NumberOfElements



Deleting a node

Bananas 21 Carrots 32Start 1

Pears •4 2

NumberOfElements



Displaying the entire list


1

CurrentNode Output





1 Bananas

CurrentNode Output





2

CurrentNode Output





2 Carrots

CurrentNode Output



Finding an element


1

CurrentNode Output



Finding an element


1 Bananas

CurrentNode Output

Carrots

Input

= ?



Finding an element


1 Bananas

CurrentNode Output

Carrots

Input

= ?

×



Finding an element


2 Carrots

CurrentNode

Carrots

InputOutput

= ?

☺



Free memory, the heap and pointers

• Many languages have a pointer type as a built-in data type.

– A variable that stores an address of a data value

• When a pointer variable is declared in a program, the compiler will

reserve a space in memory for the pointer but no space is reserved

for the values it can point to.

• The memory space is allocated when required at run time from a

pool of memory locations called the heap.

• This is known as dynamic allocation.

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List and Pointers Lesson