week14Pointers_II. pointers pemrograman dasar C++.pptx

CSC113:
COMPUTER PROGRAMMING
(THEORY = 03, LAB = 01)
Momina Moetesum
Computer Science Department
Bahria University, Islamabad

3
REFERENCE VARIABLES EXAMPLE
#include <iostream.h>
// Function prototypes
(required in C++)
void p_swap(int *, int *);
void r_swap(int&, int&);
int main (void){
int v = 5, x = 10;
cout << v << x << endl;
p_swap(&v,&x);
r_swap(v,x);
return 0;
}
void r_swap(int &a, int &b)
{
int temp;
temp = a; (2)
a = b; (3)
b = temp;
}
void p_swap(int *a, int *b)
{
int temp;
temp = *a; (2)
*a = *b; (3)
*b = temp;
}

4
POINTER EXPRESSIONS AND POINTER
ARITHMETIC
 Pointer arithmetic
 Increment/decrement pointer (++ or --)
 Add/subtract an integer to/from a pointer( + or += , - or -=)
 Pointers may be subtracted from each other
 Pointer arithmetic is meaningless unless performed on an
array
 5 element int array on a machine using 4 byte ints
 vPtr points to first element v[ 0 ], which is at location
3000
 vPtr = 3000
 vPtr += 2; sets vPtr to 3008
 vPtr points to v[ 2 ]
pointer variable vPtr
v[0] v[1] v[2] v[4]
v[3]
3000 3004 3008 3012 3016
location

5
POINTER EXPRESSIONS AND
POINTER ARITHMETIC
 Subtracting pointers
 Returns the number of elements between two
addresses
vPtr2 = v[ 2 ];
vPtr = v[ 0 ];
vPtr2 - vPtr == 2
 Pointer comparison
 Test which pointer points to the higher numbered
array element
 Test if a pointer points to 0 (NULL)
if ( vPtr == ‘0’ )
statement

6
VOID POINTER
 Pointers assignment
 If not the same type, a cast operator must be used
 Exception: pointer to void (type void *)
 Generic pointer, represents any type
 No casting needed to convert a pointer to void pointer
 void pointers cannot be dereferenced

7
THE RELATIONSHIP BETWEEN
POINTERS AND ARRAYS
 Arrays and pointers closely related
 Array name like constant pointer
 Pointers can do array subscripting operations
 Having declared an array b[ 5 ] and a pointer bPtr
 bPtr is equal to b
bptr == b
 bptr is equal to the address of the first element of b
bptr == &b[ 0 ]

8
THE RELATIONSHIP BETWEEN
POINTERS AND ARRAYS
 Accessing array elements with pointers
 Element b[ n ] can be accessed by *(bPtr + n)
 Called pointer/offset notation
 Array itself can use pointer arithmetic.
 b[ 3 ] same as *(b + 3)
 Pointers can be subscripted (pointer/subscript
notation)
 bPtr[ 3 ] same as b[ 3 ]

EXAMPLE
//using subscript and pointer notations with
arrays
#include<iostream>
using namespace std;
int main()
{
int b[]={10,20,30,40};
int *bPtr=b;
cout<<“Array printed with:”<<endl;
cout<<“ Array subscript notation” <<endl;
for (int i=0; i<=3; i++)
cout<<“b[”<<i<<“]=”<<b[i]<<endl;
cout<<endl<<“Array/offset notation”<<endl;
for(int offset=0;offset<=3;offset++)
cout<<“*(b+”<<offset<<“)=”
<<*(b+offset)<<endl;
cout<<“ Pointer subscript notation”
<<endl;
for (int i=0; i<=3; i++)
cout<<“bPtr[”<<i<<“]=”<<bPtr[i]<<
endl;
cout<<“Pointer/offset notation <<endl;
for(int offset=0;offset<=3;offset++)
cout<<“*(bPtr+”<<offset<<“)=”<<
*(bPtr+offset)<<endl;
return 0;
}

OUTPUT
Array printed with
Array subscript notation
b[0]=10
b[1]=20
b[2]=30
b[3]=40
Pointer offset notation where the pointer is the array name
*(b+0)=10
*(b+1)=20
*(b+2)=30
*(b+3)=40
Pointer subscript notation
bPtr[0]=10
bPtr[1]=20
bPtr[2]=30
bPtr[3]=40
Pointer/offset notation
*(bPtr+0)=10
*(bPtr+1)=20
*(bPtr+2)=30
*(bPtr+3)=40

EXAMPLE
//Copying a string using array notation
and pointer notation
#include<iostream>
void copy1(char *, const char *);
void copy2(char *, const char *);
int main()
{
char string1[10], *string2=“Hello”;
char string3[10],string4[]=“Good
bye”;
copy1(string1, string2);
cout<<“string1=”<<string1<<endl;
copy1(string3, string4);
cout<<“string3=”<<string3<<endl;
return 0;
}
//copy s2 and s1 using array notation
void copy1(char *s1, const char *s2)
{
for(int i=0; (s1[i]=s2[i])!=‘0’;i++)
; //do nothing
}
//copy s2 and s1 using pointer
notation
void copy1(char *s1, const char *s2)
{
for( ; (*s1=*s2)!=‘0’; s1++,s2++)
; //do nothing
}

OUTPUT
string1 =Hello
string3=Good Bye

13
ARRAYS OF POINTERS
 Arrays can contain pointers
 Commonly used to store an array of strings
char *suit[ 4 ] = {"Hearts", "Diamonds",
"Clubs", "Spades" };
 Each element of suit is a pointer to a char * (a string)
 The strings are not in the array, only pointers to the
strings are in the array
 suit array has a fixed size, but strings can be of any
size
suit[3]
suit[2]
suit[1]
suit[0] ’H’ ’e’ ’a’ ’r’ ’t’ ’s’
’
0’
’D’ ’i’ ’a’ ’m’ ’o’ ’n’ ’d’ ’s’
’
0’
’C’ ’l’ ’u’ ’b’ ’s’
’
0’
’S’ ’p’ ’a’ ’d’ ’e’ ’s’
’
0’

14
CASE STUDY: A CARD SHUFFLING
AND DEALING SIMULATION
 Card shuffling program
 Use an array of pointers to strings, to store suit names
 Use a double scripted array (suit by value)
 Place 1-52 into the array to specify the order in which the cards are dealt
deck[2][12] represents the King of Clubs
Hearts
Diamonds
Clubs
Spades
0
1
2
3
Ace Two Three FourFive SixSeven
Eight
NineTen JackQueen
King
0 1 2 3 4 5 6 7 8 9 10 11 12
Clubs King

15
FUNCTION POINTERS
 Pointers to functions
 Contain the address of the function
 Similar to how an array name is the address of its first
element
 Function name is starting address of code that defines
function
 Function pointers can be
 Passed to functions
 Stored in arrays
 Assigned to other function pointers

16
FUNCTION POINTERS
 Example: bubblesort
 Function bubble takes a function pointer
 The function determines whether the the array is sorted
into ascending or descending sorting
 The argument in bubble for the function pointer
bool ( *compare )( int, int )
tells bubble to expect a pointer to a function that
takes two ints and returns a bool
 If the parentheses were left out
bool *compare( int, int )
would declare a function that receives two integers
and returns a pointer to a bool

 2000 Deitel & Associates, Inc.
Outline
1 // Fig. 5.26: fig05_26.cpp
2 // Multipurpose sorting program using function pointers
3 #include <iostream>
4
8
9 #include <iomanip>
10
12
13void bubble( int [], const int, bool (*)( int, int ) );
14bool ascending( int, int );
15bool descending( int, int );
16
17int main()
18{
19 const int arraySize = 10;
20 int order,
21
22 a[ arraySize ] = { 2, 6, 4, 8, 10, 12, 89, 68, 45, 37 };
23
24 cout << "Enter 1 to sort in ascending order,n"
25 << "Enter 2 to sort in descending order: ";
26 cin >> order;
27 cout << "nData items in original ordern";
28
29 for ( counter = 0; counter < arraySize; counter++ )
30 cout << setw( 4 ) << a[ counter ];
31
32 if ( order == 1 ) {
33 bubble( a, arraySize, ascending );
34 cout << "nData items in ascending ordern";
counter,

Outline
35 }
36 else {
37 bubble( a, arraySize, descending );
38 cout << "nData items in descending ordern";
39 }
41 for ( counter = 0; counter < arraySize; counter++ )
42 cout << setw( 4 ) << a[ counter ];
44 cout << endl;
45 return 0;
46}
47
48void bubble( int work[], const int size,
49 bool (*compare)( int, int ) )
50{
51 void swap( int * const, int * const ); // prototype
52
53 for ( int pass = 1; pass < size; pass++ )
55 for ( int count = 0; count < size - 1; count++ )
57 if ( (*compare)( work[ count ], work[ count + 1 ] ) )
58 swap( &work[ count ], &work[ count + 1 ] );
59}
60
61void swap( int * const element1Ptr, int * const element2Ptr )
62{
63 int temp;
64
65 temp = *element1Ptr;
66 *element1Ptr = *element2Ptr;
67 *element2Ptr = temp;

Outline
Program output
69
70bool ascending( int a, int b )
71{
72 return b < a; // swap if b is less than a
73}
74
75bool descending( int a, int b )
76{
77 return b > a; // swap if b is greater
than a
78}
Enter 1 to sort in ascending order,
Enter 2 to sort in descending order: 1
Data items in original order
2 6 4 8 10 12 89 68 45 37
Data items in ascending order
2 4 6 8 10 12 37 45 68 89
Enter 1 to sort in ascending order,
Enter 2 to sort in descending order: 2
Data items in original order
2 6 4 8 10 12 89 68 45 37
Data items in descending order
89 68 45 37 12 10 8 6 4 2

20
DYNAMIC MEMORY ALLOCATION
 Dynamic Memory Allocation
 The new operator
 The delete operator
 Dynamic Memory Allocation for Arrays

21
DYNAMIC MEMORY ALLOCATION
 Static memory - where
global and static variables live
 Heap memory -
dynamically allocated at
execution time
- "managed" memory
accessed using pointers
 Stack memory - used by
automatic variables
In C and C++, three types of memory are used by programs:

22
3 KINDS OF PROGRAM DATA
 STATIC DATA: Allocated at compiler time
 DYNAMIC DATA: explicitly allocated and
deallocated during program execution by C++
instructions written by programmer using
operators new and delete
 AUTOMATIC DATA: automatically created at
function entry, resides in activation frame of
the function, and is destroyed when returning
from function

23
DYNAMIC MEMORY
ALLOCATION
 In C, functions such as malloc() are used to
dynamically allocate memory from the Heap.
 In C++, this is accomplished using the new
and delete operators
 new is used to allocate memory during
execution time
 returns a pointer to the address where the object is to be
stored
 always returns a pointer to the type that follows the new

OPERATOR NEW SYNTAX
new DataType
new DataType [IntExpression]
 If memory is available, in an area called the heap (or
free store) new allocates the requested object or array,
and returns a pointer to (address of ) the memory
allocated.
 Otherwise, program terminates with error message.
 The dynamically allocated object exists until the delete
operator destroys it.
24

25
OPERATOR NEW
char* ptr;
ptr = new char;
*ptr = ‘B’;
cout << *ptr;
NOTE: Dynamic data has no variable name
2000
???
ptr
5000
5000
‘B’

OPERATOR DELETE SYNTAX
delete Pointer
delete [ ] Pointer
 The object or array currently pointed to by Pointer
is deallocated, and the value of Pointer is
undefined. The memory is returned to the free
store.
 Good idea to set the pointer to the released
memory to NULL
 Square brackets are used with delete to deallocate
a dynamically allocated array. 26

27
OPERATOR DELETE
char* ptr;
ptr = new char;
*ptr = ‘B’;
cout << *ptr;
delete ptr;
5000
5000
‘B’
2000
ptr
???
NOTE:
delete deallocates the
memory pointed to by ptr

EXAMPLE
#include <iostream>
int main()
{
int n, *p, c;
cout << "Enter an integern";
cin >> n;
p = new int[n];
cout << "Enter " << n << " integersn";
for ( c = 0 ; c < n ; c++ )
cin >> p[c];
cout << "Elements entered by you aren";
for ( c = 0 ; c < n ; c++ )
cout << p[c] << endl;
delete[] p;
return 0;
}

week14Pointers_II. pointers pemrograman dasar C++.pptx

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