Learning C++ - Pointers in c++ 2

Section Outline
• Introduction to Memory
• Pointers
• Arrays
• Scope
2

Section Outline
• Pointers
• Arrays
• Scope
3

Introduction to Memory
• Problems related to pointer in C++
Arrays
Function’s return
Importance of working with memories
4
Memory space (a cell)
that has a value
.
.
1000
1001
1002
.
.
A Pointer

Introduction to Memory
• More Details:
5
Memory space (a cell)
that has a value
.
.
1000
1001
1002
.
.
A Pointer 0 1 1 0 1 0 0 1

Section Outline
• Pointers
• Arrays
• Scope
6

(this type can accept any type in assignment
but when we want to assignment to other
variable we must do a cast)
• Definition of a Pointer in C++
Type * Name = NULL;
(it means ptrName points to nowhere , defines in <iostream.h>)
e.g.
int * ptr1;
void * ptr2
Pointers
7
Why initialization is
important?

• e.g.
int main()
{
void var1;
var1 = ‘A’;
var1 = 1.322;
float var2 = ( float ) var1;
}
Pointers
8

• Note :
– & has two means in two case
• Address fetch
int var1 ;
cout << & var1;
• In calling function
– * has two means in two case
• In definition of a variable, near the type means we are
defining a pointer
• Otherwise ,as a operator , get the value of a pointer
int a = 23;
int * pointer = a;
cout << *pointer;
Pointers
9
Out put : 23

• Notice to this code:
void main()
{
int var1 = 25;
int * var2 = & var1;
cout<<var1<<“n”<<var2<<“n”<<*var2;
}
Output: 25
0x9934344
25
Pointers(cont.)
10
Return address

Pointers(cont.)
• Pointer`s access
int a;
int *ptr = a;
* ptr = 20;
*(ptr+1) = 23;
ptr++;
11
20
23
XXXXXXXX
(1) 1001: ptr
(2) 1002: ptr
(3) 1003: ptr

Section Outline
• Pointers
• Arrays
• Scope
12

• Definition of an array (literature)
• Dimension
o1D: has been exampled latter
o2D : arrangement in memory
13
1001
1002
1003
0
3
6
1
4
8
2
5
7
Arrays
In C++
In Fortran

Arrays(cont.)
• What is related between array and pointers:
i. Definition of an array in C++
ii. Array`s name
iii. Combining array and pointer concepts
iv. Array`s bound
14

i. Definition of an array in C++
type Name[dimensions];
int Ar_name[5];
int Ar_name[10][20];
Note : if we define an array with 5 cell then C++ count them from
zero.
(for , while, do while)
 First things in C++ usually
has the zero number.
15
Cell No. 0
Cell No. 1
Cell No. 2
Cell No. 3
Arrays(cont.)

ii. Array`s name!
 array`s name has the address of the first cell in the memory.
int myArray[5];
int * myPtr = myArray;
int myArray[5]; int counter = 0;
int counter = 0;
for(; counter< 5; counter++) for(; counter< 5; counter++)
{ {
} }
16
myArray[counter]
= counter;
myPtr[counter]
= counter;
Arrays(cont.)

iii. Combining array and pointer concepts
define a pointer : int ptr[];
iv. Array`s bound
 In C++ we must be cautious about array boundaries(otherwise a
Exception appear)
17
0
1
2
1000(my_array)
1001
1002(my_array+2)
?????
Arrays(cont.)

• Initializing array
 It`s related to use to initializing an array or not , but it`s
better to initialize arrays, specially in calculation cases
 How to initialize an array
» int numbers[4] = {1, 3, 708, -12};
» float floats[3][2] = {{1.0,5.0},{0.5,3.1},{6,0.15}};
» char myArray [5] = {‘A’,’b’,’E’,’d’,’q’};
» Do this in a loop by initialize each after another
int myArray[10][5];
for(int i=0; i<10; i++)
for(int j=0; i<5; j++)
myArray[i][j] = 0;
18
Every where in C++ we can define a
variable
At some commands such as for, if, while,
do while the line just after them do not
need { } (or the first command after
these has impressed by themselves)
Arrays(cont.)

• Note:accolade
int myArray[5]; int myArray[5];
int counter = 0; int counter = 0;
for(; counter< 5; counter++) for(; counter< 5; counter++)
{
}
19
myArray[counter]
= counter; myPtr[counter]
= counter;
A = B+1;
Arrays(cont.)

Section Outline
• Pointers
• Arrays
• Scope
20

Scope
• Every variable can just appear and use exactly in a
deterministic area that named “scope” .
• This rules over all the variable , even pointers
e.g.
int i = 0;
if(myVar != 1)
{
int i = 123;
}
cout << i;
21
Out put is : 0

In future :
i. Functions
ii. Class and related concepts
iii.ERRORS
22

Learning C++ - Pointers in c++ 2

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Learning C++ - Pointers in c++ 2