CS201 Computer Sciences Faculty IEU

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CS201Computer Sciences FacultyIEU
Süleyman Kondakci suleyman_at_cryptocode.net
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Pointers

• Pointer variable containing address of another
  variable
• int x 5 / data variable /
• int y 7 / data variable /
• int ptr x / address operator /

5
7
1200
ptr
x
y
ptr 10
7
10
1200
y
ptr
x
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Pointers - 1

• Pointer variable containing address of another
  variable
• float f / data variable /
• float f_addr / pointer variable /
• f_addr f / address operator /

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Pointers - 2
f_addr 3.2 / indirection operator
/ float gf_addr /
indirectiong is now 3.2 / f 1.3
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Arrays and Pointers
An array name by itsels is an address or pointer
value! define N 100 int aN, i, p, q, sum
0 p a / is equivalent to p a0 / p
a 1 / is equivalent to p a1 / int ai
/ is equivalent to (a i) / Here (a i) is
the dereferencing of the expressin a i that
points i elements positions past in a p a /
points to the base of array a / q p 1 /
equivalent to q a1 / printf(d\n, q p)
printf("d\n", (int) q - (int) p) for (p a
p ltaN p) sum p for (i 0 i lt N i)
sum (a i)
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Pointer Arithmetic
int main(int argc, char argv) double a2,
p, q p a / points to the base of array a
/ q p 1 / equivalent to q a1
/ printf("\n") pri
ntf(" p d", p) printf("\n q d", q
) printf("\n q - p d", q - p) printf("\n q
- p d\n", (int) q - (int) p) printf(" a0
d", a0 ) printf("\n a1 d a1 )
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Pointer Example
include ltstdio.hgt void main(void) int
j int ptr ptrj / initialize ptr
before using it / / ptr4 does NOT
initialize ptr / ptr4 / j lt- 4
/ jptr / j lt- ??? /
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More pointers
int month12 / month is a pointer to base
address 430/ month3 7 / month address
3 int elements gt int at address (43034)
is now 7 / ptr month 2 / ptr points to
month2, gt ptr is now (4302 int
elements) 438 / ptr5 12 / ptr
address 5 int elements gt int at
address (43454) is now 12. Thus, month7 is
now 12 / ptr / ptr lt- 438 1
size of int 442 / (ptr 4)2 12 /
accessing ptr6 i.e., array9 /

• Now , month6, (month6), (month4)2,
  ptr3, (ptr3) are all the same integer
  variable.

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Pointers Summary

• int a 10, b 2, p
• p a // p is assigned address of a
• b p // b is assigned the value pointed by p
• b p is equivalent to b a
• An array name is an address or a pointer value
• Arrays and pointers can be subscripted
• int A10, p
• int b ai is equivalent to int b (a i)
• int c pi is equivalent to int c (p i)
• p a is equivalent to p a0
• p a 1 is equivalent to p a1

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Pointers Summary
All will sum the array ellements 1) for (p a
p ltaN p) sum p 2) for (i 0 i lt N
i) sum (a i) 3) p a for (i 0 i lt
N i) sum pi
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Call-by-value
Whenever variables are passed as arguments to a
function, their values are copied to the function
parameters void main() int a20 int
b30 swap (a, b) printf(d d , a,
b) void swap(int x, y) int
tmp tmpx xy ytmp
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Call-by-reference
Pointers are passed as arguments to a function,
their addresses are assigned to the function
parameters defined as pointers vioid
main() int a20 int b30 swap (a,
b) printf(d d , a, b) void swap(int
x, y) int tmp tmp x // get value
pointed by x. x y // assign value pointed
by y to x y tmp
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Structures
include ltstdio.hgt struct birthday int
month int day int year main()
struct birthday mybday mybday.day1
mybday.month1 mybday.year1977 printf(I was
born on d/d/d, birth.day,
birth.month, birth.year)
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More on Structures
struct person char name41 int age
float height struct / embedded or
nested structure / int month int
day int year birth struct
person me me.birth.year1977 struct
person class60 / array of info about
everyone in class / class0.nameCS206
class0.birth.year1971
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Accessing Members of Structures
struct exp char c int i float
arr10 struct exp exp1 struct exp
expPtr exp1.c A i 20 prinf(cd ,
exp1.c, exp1.i) expPtr-gtcB
expPtr-gti30 prinf(cd , expPtr-gtc,
expPtr-gti) expPtr exp1 prinf(cd ,
expPtr-gtc, expPtr-gti) prinf(cd ,
(expPtr).c, (expPtr).i)
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typdef Synonym for a data type
typedef int numbers numbers a_number / same
as int a_number / typedef struct person
Person Person me / same as struct
person me / typedef struct person
Personptr Personptr ptrtome / same as
struct person ptrtome/

• Easier to remember
• Clean code

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Linked Lists

• Nodes Represent data storage points
• Pointers are used to handle nodes

A node
int a char c char name kerem
NULL
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Linked List Operations

• Creating a list element,
• Prepending elements on top of lists,
• Inserting elements into lists,
• Appending to end of lists,
• Finding/searching elements in the list
• Sorting elements,
• Deleting,
• Moving elements around in the list.

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Linked List Types

• Single linked lists

next
Double linked lists
NULL
Circle linked lists
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Linked Lists
struct list int data struct list
next a
struct list a, b,c
a.data 1 b.data 2c.dat 3 a.nextb.nextc.
next NULL
a.next b b.next c
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Linear Linked Lists
include ltassert.hgt include ltstdio.hgt include
ltstdlib.hgt define MAXLINE 100 typedef char
DATA / will use char in examples
/ struct linked_list DATA d struct
linked_list next typedef struct
linked_list ELEMENT typedef ELEMENT LINK
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Linear Linked Lists
LINK head head malloc(sizeof(ELEMENT))
head-gtd A head-gtnext NULL
/ Lets add a second element / head -gtnext
malloc(sizeof(ELEMENT)) head-gtnext-gtd
B head-gtnext -gtnext NULL
/ Lets add a 3rd element / head -gtnext-gtnext
malloc(sizeof(ELEMENT)) head-gtnext-gtd -gtnext
C head-gtnext -gtnext -gtnext NULL
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Creating a List 1st Declare the List
include ltassert.hgt include ltstdio.hgt include
ltstdlib.hgt define MAXLINE 100 typedef char
DATA / will use char in examples / struct
linked_list DATA d struct linked_list
next typedef struct linked_list
ELEMENT typedef ELEMENT LINK
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Creating a List Using Iteration
include "list.h" LINK s_to_l(char s) LINK
head NULL, tail int i if (s0 !
'\0') / first element / head
malloc(sizeof(ELEMENT)) head -gt d s0
tail head for (i 1 si ! '\0'
i) / add to tail / tail -gt next
malloc(sizeof(ELEMENT)) tail tail -gt
next tail -gt d si tail
-gt next NULL / end of list / return
head
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Creating a List Using Recursion
include "list.h" LINK string_to_list(char s)
LINK head if (s0 '\0') /
base case / return NULL else
head malloc(sizeof(ELEMENT)) head -gt d
s0 head -gt next string_to_list(s
1) return head
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Count Elements of a List Using Iteration
include "list.h" int count_list(LINK head)
int count for ( head ! NULL head head -gt
next) count return count
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Count Elements of a List Using Recursion
include "list.h" int count_list(LINK head)
if (head NULL) return 0 else return(1
count_list(head -gt next))
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Print Elements in a List Using Iteration
include "list.h" void wrt_list(LINK head)
LIST p if (head NULL) printf(NULL
list) else for (p head p ! NULL p p
-gt next) putchar(p -gt d)
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Print Elements in a List Using Recursion
include "list.h" void wrt_list(LINK head) if
(head NULL) printf(NULL list) Else
printf(c ?, head -gt d) wrt_list(head
-gtnext)
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Insertion of Elements in a List
include "list.h" Void insert(LINK p1, LINK p2,
LINK q) Assert (p1-gt next p2) p1-gtnext
q q-gtnext p2
initially
p2
p1
q
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Delete Elements in a List Using Iteration
include "list.h" void delete(LINK head)
LIST p if (head NULL) printf(NULL
list) else for (p head p ! NULL p p
-gt next) free(p)
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Delete Elements in a List Recursively
include "list.h" void elete_list(LINK
head) if (head ! NULL) delete_list(head
-gtnext) free(head)
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Queue Implementations
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Link-list based implementation
queue
Queue First-In-First-Out (FIFO) data structure
cnt
front
rear
elem
elem
elem
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The header file queue.h
define EMPTY 0 define FULL
10000 typedef unsigned int
data typedef enum false, true
boolean struct elem / an element in
the queue / data d struct elem
next typedef struct elem elem struct
queue int cnt / a count of the
elements / elem front / ptr to the
front element / elem rear / ptr to the
rear element / typedef struct queue queue
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The header file queue.h (cont d)
void initialize(queue q) void
enqueue(data d, queue q) data
dequeue(queue q) data front(const queue
q) boolean empty(const queue q) boolean
full(const queue q)
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Basic queue routines (cont d)
include "queue.h" void initialize(queue q)
q -gt cnt 0 q -gt front NULL q -gt rear
NULL data dequeue(queue q) data d
elem p d q -gt front -gt d p q -gt
front q -gt front q -gt front -gt next q
-gt cnt-- free(p) return d
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Basic queue routines (cont d)
void enqueue(data d, queue q) elem p
p malloc(sizeof(elem)) p -gt d d p -gt
next NULL if (!empty(q)) q -gt rear
-gt next p q -gt rear p else
q -gt front q -gt rear p q -gt cnt
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Basic queue routines (cont d)
data front(const queue q) return (q -gt front
-gt d) boolean empty(const queue q)
return ((boolean) (q -gt cnt EMPTY)) boolean
full(const queue q) return ((boolean) (q -gt
cnt FULL))
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• Array Based Queue Implementation

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Array Based Implementation

• Auxiliary queue operations
• front() returns the element at the front without
  removing it
• size() returns the number of elements stored
• isEmpty() returns a Boolean var indicating
  whether the queue is empty
• isFull() returns a Boolean var indicating
  whether the queue is full
• DisposeQueue(Queue Q) Deletes elements of queue Q

• The Queue ADT stores arbitrary objects
• Insertions and deletions follow the first-in
  first-out scheme
• Insertions are at the rear of the queue and
  removals are at the front of the queue
• Main queue operations
• Enqueue(Element e) inserts an element o at the
  end of the queue
• Dequeue() removes and returns the element at the
  front of the queue

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Utility routine
include ltstdio.hgt include ltstdlib.hgt define
Error( Str ) FatalError( Str ) define
FatalError(Str) fprintf(stderr, "s\n", Str),
exit( 1 )
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Queue routines (queue.h)
struct QueueRecord int Capacity
int Front int Rear
int Size ElementType Array
QueueRecord typedef int ElementType typedef
struct QueueRecord ELEMENT typedef ELEMENT
Queue
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Queue routines (queue.h contd)
bool IsEmpty( Queue Q ) bool IsFull( Queue Q
) Queue CreateQueue( int MaxElements ) void
DisposeQueue( Queue Q ) void MakeEmpty( Queue Q
) void Enqueue( ElementType X, Queue Q
) ElementType Front( Queue Q ) void Dequeue(
Queue Q ) ElementType FrontAndDequeue( Queue Q )
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Queue routines (queue.c)
include "queue.h" include "error.h" ifndef
bool define bool define true 1 define false
0 endif define MinQueueSize ( 5 ) bool
IsEmpty( Queue Q ) return Q-gtSize
0 bool IsFull( Queue Q ) return (Q-gtSize
Q-gtCapacity)
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Queue routines (queue.c contd)
Queue CreateQueue( int MaxElements ) Queue
Q if( MaxElements lt MinQueueSize ) Error(
"Queue size is too small" ) Q malloc( sizeof(
ELEMENT) ) if( Q NULL ) FatalError( "Out
of space !!!" ) Q-gtArray malloc( sizeof(
ElementType ) ( MaxElements ) if(
Q-gtArray NULL ) FatalError( "Out of
space!!!" ) Q-gtCapacity MaxElements MakeEmpt
y( Q ) return Q
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Queue routines (queue.c contd)
void MakeEmpty( Queue Q ) Q-gtSize
0 Q-gtFront 1 Q-gtRear
0 void DisposeQueue( Queue Q ) if( Q !
NULL ) free( Q-gtArray )
free( Q ) static int Succ( int Value, Queue
Q ) if( Value Q-gtCapacity ) Value
0 return Value
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Queue routines (queue.c contd)
void Enqueue( ElementType X, Queue Q )
if( IsFull( Q ) ) Error( "Full queue" )
else Q-gtSize Q-gtRear Succ( Q-gtRear, Q
) Q-gtArray Q-gtRear X
ElementType Front( Queue Q ) if(
!IsEmpty( Q ) ) return Q-gtArray Q-gtFront
Error( "Empty queue" ) return 0 /
Return value used to avoid warning /
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Queue routines (queue.c contd)
void Dequeue( Queue Q ) if( IsEmpty( Q )
) Error( "Empty queue" ) else
Q-gtSize-- Q-gtFront Succ( Q-gtFront, Q
) ElementType FrontAndDequeue(
Queue Q ) ElementType X 0 if(
IsEmpty( Q ) ) Error( "Empty queue" ) else
Q-gtSize-- X Q-gtArray
Q-gtFront Q-gtFront Succ( Q-gtFront, Q
) return X
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Queue routines (queue.c contd)
include ltstdio.hgt include "queue.c" int main( )
Queue Q int i Q CreateQueue( 12 )
for( i 0 i lt 10 i ) Enqueue( i, Q )
while( !IsEmpty( Q ) ) printf(
"d\n", Front( Q ) ) Dequeue( Q )
DisposeQueue( Q ) return 0