Structures and pointers-2_240731_192519.pdf

Pointers

1. CHAPTER 1

2. a
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3. Structures
Structure is a user-defined data type of C++ to
represent a collection of logically related data items, which
may be of different types, under a common name.
Arrays allow to define type of variables that
can hold several data items of the same kind.
Similarlystructureis another user defined data type
available in C++ that allows to combine data items of
different kinds.
•Structure is a user defined data type
•It is a collection of heterogeneous data items
•It can be defined using the key word STRUCT
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--
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4. Defining a Structure
Todefineastructure,youmustusethestructstatement.Thestructstatement
definesanewdatatype,withmorethanonemember.Theformatofthestruct
statementisasfollows−
structstructuretag
{
data_typevariable;
data_typevariable;
data_typevariable;
…………………………… ..
…………………………… ..
data_typevariable;
}[oneormorestructurevariables];
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↑
T-
Y
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⑭
--x

5. Eg:-
Structstudent
{
int adm_no;
char name[20];
char group[20];
float fee;
};
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-
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e

6. Structdate
{
int dd;
int mm;
int yy;
};
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7. Struct strdate
{
int day;
char month[10];
int year;
};
--=
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8. Variable declaration and memory allocation
Structure variable can be declared by the syntax:-
Structstructure-namestructure-variable;
structstructure_tag var1, var2, ..., varN;
or
structure_tag var1, var2, ..., varN;
D
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9. Eg:
Structstudent s;
Student s;
↑
I
↑
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10. date dob, today; OR struct date dob,
today;
strdateadm_date, join_date;
↓
↓ ↓
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--.
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↑
T

11. Memory allocation of structure
variable

12. A C++ compiler allocate separate memory location for
each and every structure members.
struct student
{
Int roll_no;
Char name[20];
Float mark;
};
Total 28 bytes
Roll_no4 byte
Name 20*1=20 byte
Mark 4 byte
I
- &
Rollno
-
-
name
mark
5

13. -
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14. Variable initialisation
structure_tagvariable={value1, value2,..., valueN};
Eg:
student s={3452, "Vaishakh", "Science", 270.00};
↓
↓I
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15. si
sti
&
= -
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16. Accessing elements of structure
The structure member can be accessed by using the
structure variable with dot(.) operator.
structure_variable.element_name
s.roll_no=5;
s.name=“abc”;
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--
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17. Write a c++programme to read and print a student details
using structure.
Usingnamespace
std;
[#
include<io
stream
I
int
main
(7
StructstudentStructStudent
S;
E
contenterMolno"
;
intcolno
; (in
S
.
colno;
[20]
;
"Inter
thename"
;
char
name Cout
L
intage
;
S
.
name
(in
>
>3·

18. Coul"Entertheage"
;
(in>S
.
age;
coutsThe
student
details
are"
;
Cout"Rollno
=
"LLS
.
colno;
Conti"
Name
=
"S
.
name;
Cout" Age
=
"LLS
.
age
;
turn
0
;
se3

19. Nested structure
It means structure with in a structure and inner most
member in a nested structure can be accessed by chaining
all the conserved structure
Variable [outer most to inner most] with member using dot
operator (.)

20. Struct pay
{
Int basic;
Int da;
};
Struct employ
{
Int id;
Char name[10];
Struct pay p;
}
Void main()
{
Struct employ e;
e.id=101;
e.name=“abc”;
e.p.basic=10000;
e.p.da=101.5;
}
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21. Elles

22. student s = {4325, "Vishal", {10, 11, 1997}, 575};
cout<<s.adm_no<<s.name;
cout<<s.dt_adm.day<<"/"<<s.dt_adm.month<<"/"<< s.dt_adm.year;
↓↓↓L ↓
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--
&admadm
.
day
;
di
y
.
al
da;
e
.
P
.

23. outer_structure_varaiable.inner_structure_variable.element
↑IT 41
↑
da
;
2.p
.

24. Array Vs Structure
255
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27
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26. Pointer
A pointer is a derived data type.
→It contain memory address of another variable.
→It can be used to access & manipulate data stored in
the memory.
lis
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27. Benefits of pointers
•Pointers are more efficient in handling arrays.
•Pointers can be used to return multiple values from a function.
•Pointers support dynamic memory management .
•Pointers provide an efficient tool for manipulating dynamic data
structures such as data structures linked list , queue.
•Pointers reduced length and complexity of a programme.
•Pointers increases the execution speed.
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28. int num=25;
a
&
A
I
----

29. variable is associated with two values :
L-value and R-value,
where L-value is the address of the variable and R-value is
its content.
Figure 1.5 shows that L-value of num is 1001 and R-value is 25
a
=
10
a
10110
-
=
-)
-
10110)
L
=
10
R
=

30. Declaring pointer variable
The declaration of a pointer variable take the following forms,
Data type * pointer_variable_name ;
Eg:
int *p;
int *ptr1;
float *ptr2;
struct student *ptr3;
X
--

31. •The address of a variable can be assigned to pointer
variable using address operator (&)
Eg:
int *p;
int a;
p=&a
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&
=
dai
=>
I

32. ptr1 = & num;
=
=

33. cout<< &num;
cout<< ptr1;
cout<< num;
cout<< *ptr1;
cout<< &ptr1;
cout<< *num;
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&
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34. cout<< &num; // 1001 (address of num) will be the output
cout<< ptr1; // 1001 (content of ptr1) will be the output
cout<< num; // 25 (content of num) will be the output
cout<< *ptr1; /* 25 (value in the location pointed to by
ptr1) will be the output */
cout<< &ptr1; // 1500 (address of ptr1) will be the output
cout<< *num; // Error!! num is not a pointer
=>
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--
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--
- -

35. The process of assigning address of a variable is known
as initialization.
initialization:- int a;
int *p=&a;
A pointer can store address of similar variable only.
Eg:- int *p;
float f;
p=&f /error
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of
i
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p
=
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36. •It is possible to make a pointer to another pointer. Thus
creating the chain of pointers.
Int x,*p1,**p2;
X=100;
P1=&x;
P2=&p1
COUT<<**p2;
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*
PI
↓
12
*
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37. •A pointer can be initialized with null or zero.
•Multiplication is not possible on pointer variable.
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38. Methods Of Memory Allocation
→The memory allocation that takes place before the execution
of the program is known as static memory allocation.
→memory is allocated during the execution of the program is
called dynamic memory allocation.
❑New : allocate
❑delete : de-allocate
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39. Dynamic operators - new and delete
The operator new is a keyword in C++ and it triggers the
allocation of memory during run-time (execution).
following syntax is used for dynamic memory allocation:
pointer_variable = new data_type;
↑
↑T

40. short * si_ptr;
float * fl_ptr;
struct complex * cx_ptr;
si_ptr = new short;
fl_ptr = new float;
cx_ptr = new complex;
--
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--
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41. -
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42. allocated memory locations can also be initialised using
the following syntax:
pointer_variable = new data_type(value);
The following examples show initialisation along with
dynamic memory allocation:
si_ptr = new short(0);
fl_ptr = new float(3.14);
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O
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14
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S 3
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43. delete operator is used with the following
Syntax :
delete pointer_variable;
The following are valid examples:
delete si_ptr;
delete fl_ptr, cx_ptr;
--
--
--

44. Memory leak
Orphaned Memory Block
If the memory allocated using new operator is not freed
using delete, that memory is said to be an orphaned memory
block
- a block of memory that is left unused, but not released for
further allocation. This memory block is allocated on each
execution of the program and the size of the orphaned block is
increased. Thus a part of the memory seems to disappear on
every run of the program, and eventually the amount of
memory consumed has an unfavorable effect. This situation is
known as memory leak.
New
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45. The following are the reasons for memory leak :
• Forgetting to delete the memory that has been allocated
dynamically (using new).
• Failing to execute the delete statement due to poor logic of
the program code.
• Assigning the address returned by new operator to a pointer
that was already pointing to an allocated object
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46. ~
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47. Operations on pointers
The operators that can be used with pointers and how these
operations are performed.

48. Arithmetic operations on pointers
si_ptr and fl_ptr
= -
----
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49. cout << si_ptr+ 1;
cout << fl_ptr+ 1;
What will be the output? Do you think that it will be 1001 and 1011?
-
0
1000
&
O
-
1000
+
&
/
100l
⑪
--

50. When we add 1 to a short int pointer, the expression returns the address of the
next location of short int type.
si_ptr+1
(1000+(1*2)=1002 (size of short int is2 bytes)
fl_ptr+1
(1010+(1*4))=1014 (size of floatis4 byte)
si_ptr+5=?
-
-
---
1000+
5x2
=
1010
2

51. si_ptr+5 = (1000+5×2)=1010
fl_ptr+3 = (1010+3×4)=1022
This kind of operation is practically wrong.
T
↓
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--

52. Because we are trying to access locations that are
not allocated for authorised use. These locations might
have been used by some other variables. Sometimes
these locations might not have been accessible due to
the violation of access rights.
→No other arithmetic operations are performed on
pointers
pointers are only incremented or decremented
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53. int *ptr1, *ptr2; // Declaration of two integer pointers
ptr1 = new int(5); /* Dynamic memory allocation (let the
address be 1000)and initialization with 5*/
ptr2 = ptr1 + 1; /* ptr2 will point to the very next
integer location with the address 1004 */
++ptr2; // Same as ptr2 = ptr2 + 1
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nau)
-
1000look//
I

54. We used arrays in such a situation. But the size should be
specified during the array declaration. This may cause
wastage or insufficiency of memory space.
Pointer and its arithmetic overcome this drawback.
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:
11
:
x
- -

55. But there is a problem in this kind of memory usage. It is not
sure that Program 1.3 will always run with any value of n.
pointer ht_ptr is initialised with the address of only one
location. The memory locations accessed using pointer
arithmetic on ht_ptr are unauthorised, since these locations
are not allocated by the OS.
We can overcome these issues by the facility of dynamic
arrays,
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56. Relational operations on pointers
Among the six relational operators, only == (equality) and
!= (non-equality) operators are used with pointers.

57. If p and q are two pointers, they may contain the address of
the same integer location or different memory locations.
This can be verified with the expressions
p==q or p!=q---
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58. Pointer and array
Figure 1.9 shows the memory allocation of an array ar[10]
of int type with 10 numbers.

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59. If ptr is an integer pointer
ptr = &ar[0];
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60. cout<<ptr; //Displays 1000, the address of ar[0]
cout<<*ptr; //Displays 34, the value of ar[0]
cout<<(ptr+1); //Displays 1004, the address of ar[1]
cout<<*(ptr+1); //Displays 12, the value of ar[1]
cout<<(ptr+9); //Displays 1036, the address of ar[9]
cout<<*(ptr+9); //Displays 19, the value of ar[9]
U
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10
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61. Can you predict the output of the statement :
cout<<ar;
output will be 1000
The address of the first location of the array
-P as
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62. The following C++ statement displays all the elements of
this array :
for (int i=0; i<10; i++)
cout<<*(ar+i)<<'\t';
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63. There is a difference between an ordinary pointer and an
array-name.
ptr++; is valid and is equivalent to ptr=ptr+1;
The statement ar++; is invalid,
Because array-name always contains the base
address of the array, and it cannot be changed.
z
D
3&
z
D
z
&
- -
y
a
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64. Dynamic array
Dynamic array is created during run time using
the dynamic memory allocation operator new.
The syntax is:
pointer = new data_type[size];
↓
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is

65. Array of strings
A array or character pointer can be used to
store only one name at a time. Here we need to refer to a
collection of strings ("Sunday", "Monday", ..., "Saturday“)
The following statement declares an array of
character pointers to handle this case:
char *name[7];

66. This array can contain a maximum of 7 strings,
where each string can contain any number of characters.
char *week[7]={"Sunday", "Monday", "Tuesday",
"Wednesday",
"Thursday", "Friday", "Saturday"};
&&&
---------- ------
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----y)
/&
⑮
B
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[2
v
- - -
·

67. Pointer and structure
structures are accessed by pointers. A structure
is defined to represent the details of employees as follows:
struct employee
{
int ecode;
char ename[15];
float salary;
};
-
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68. employee *eptr ;
*
eptr
·
ecode;Y
-
salary
;
1a-7
de
;
epepto
-
>
eco
encue;
-
>epto

69. It is clear that eptr is a pointer that can hold the address of
employee type data. The statement:

eptr = new employee; -

70. -

71. structure is accessed in terms of its elements with the following
format : structure_variable.element_name
have to use the pointer eptr. The syntax for accessing the
elements of a structure is as follows:
structure_pointer->element_name
-
C
.
id;
e
.
name;
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- --

72. Self referential structure
Self referential structure is a structure in which one of the
elements is a pointer to the same structure.

73. Self referential structure is a powerful tool of C and C++
languages that helps to develop dynamic data structures
like linked list, tree, etc
The memory locations are scattered, but there will be
a link from one location to another
-
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structNoch
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int
data
;
Node
*
next
;
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