#02 Pointers242-207 FUNDAMENTAL PROGRAMMING I

DEPARTMENT OF COMPUTER ENGINEERING, PSU

1

v1.1

Contents

Introduction to Pointer

Call by Reference

Pointer & Array

Pointer & Structure

2

Pointers

To code Call by Reference

To build lists, queues, stacks, trees, etc.

Overview:

Recap: Variable is just a box in memory.

3

x

ptr1 ptr2

Declaring a Pointer

Read this declaration backwards:

can contain the address of an integer

variable

can point to an integer variable

Alternative declarations

4

!

"

""

"!!"

Assign value to a Pointer

in front of variable return memory address of the

variable

Usually, we don't care what the address value of

is.

every time this program run, is the same.

5

Dereferencing a Pointer

To access the variable or memory location that

the pointer points to

* and & are complements of each other

*&x => x

6

Value vs. Reference 7

#$

%

&

$

'(

&

#$

%

&

" $

(

&

Call by Reference 8

main:

allocate memory for a

a = 3;

call inc() with &a

inc:

allocate memory for ptr

ptr = &a; (somehow)

*ptr +=1;

main:

...

#$

%

&

" $

(

&

Array

Pointer (Point-of-View)

Automatically allocate memory for 5 integers

Create a as a constant pointer

a point to the beginning of the array

a[0], *a gives you 0

9

0 1 2 3 4

a

(constant pointer)

Passing array to functions 10

#$

)%*$&

#!

+++

&

"#! )*$

)*,

&

0 1 2

a

a is known in main()

b b is known in modify()

Pointer Arithmetic

11

0 1 2 3 4

a

(constant pointer)

p q

0 1 2 3 4

q q

Case Study - Summation

Pattern I: General style

'# $

-

- .(($

()*

&

'

&

12

Case Study - Summation

Pattern II: Pointer declaration

'# $

-

- .(($

()*

&

'

&

13 Case Study - Summation

Pattern III: Pointer arithmetic

'# $

-

- .(($

(

&

'

&

14

Case Study - Summation

Pattern IV: Pointer arithmetic, pointer sliding

'# $

-

- .(($

(

&

'

&

15 Case Study - Summation

Pattern V: Pointer comparison

'# $

-

$

(

&

'

&

16

0 1 2 3

a b

DO NOT Confuse!

)%*

!

)%*

!

17 Pointer to Structure

' $

!

&

! ' /

#$

/

/

0

&

Declaration: same as

pointer to primitive types

-> is a special operator

to access structure

member from pointer.

18

+ + 12

+! +! 12!

Case Study: Line Distance 19

#$

/$&

/$-&

++++++

&

//$

123 12

! 12!3 12!

'4(!!

&

DANGER! 20

/

12

/

/

12

/)%*

)*12

/

/)%*

)-*

)*

)*

)*12