Data Structures
SWE
👉
Pointers
😲
How memory works ?
Int x ;
x = 12;
OR
Int x = 12;
Float y = 3.99;
1 2
3. 99
X
Y
Beside its name, Any thing stored in the memory ( such as variables ),
is allocated to a unique address.
We can access any variable by its name or its address .
To get the variable address we use address operator ( & )
X
0
1
1
Y
2
8
9
10
16
17
18
24
25
26
2
3
4
5
6
7
11
12
13
14
15
21
22
23
29
30
31
19
27
3.
20
28
99
Cout << y; // OUTPUT -> 3.99 ( Print value of y )
cout << &y; // OUTPUT -> 19
( Print address of y )
NOTE :
THE Addresses used on this example is not real ones, its only for
declaration
Real addresses is represented on hexadecimal form
Usually starts with 0x to declare that it is a hexa form
Ex:
0x5a01
0x7a09
0x00000123
Pointers
> Pointer is variable that holds an address
> alternate way to access memory locations
Pointer definition
int *ptr;
or
int* ptr;
( * ) is called the indirection operator
How to assign a value to a pointer
int num = 25; // assign the value 25 to the variable num
int *p; // definition of the pointer
p = &num; // pointed to the valeu 25 by the pointer p
Memory
num
p
25
0x0012
Test
Test
Cout << num; // 25
// 0x0012
Cout << p;
Cout << &num; // 0x0012
Cout << &p; // 0x0123
Cout << *p; // 25
*p = 20;
Cout << num; //20
GDSC
Benha University
One variable can be denoted by multiple pointers
Ptr_1
0x0016
int num =5;
int *ptr_1, *ptr_2, *ptr_3;
ptr_1 = &num;
Ptr_2
0x0016
ptr_2 = &num;
ptr_3 = ptr_1;
num
Ptr_3
0x0016
*ptr_1
*ptr_2
*Ptr_3
Pointer to pointer
( double pointer )
Pointer is a variable , so I can point to it with another pointer
0x0016
int num = 8;
int *ptr_1, **ptr_2;
0x0016
ptr_1 = &num;
ptr_2 = &ptr_1;
Ptr_2
Ptr_1
0x0a13
0x0016
0x6a19
0x0a13
num
0x0016
note while using pointers
NULL initialization
Ptr_1
int *ptr_1 = 0;
NULL
int num = 12;
Ptr_1
ptr_1 = &num;
0x0016
initial value must have the correct type
float num = 0;
int *ptr = &num;
// ERROR
float *ptr = &num; // correct
num
0x0016
Pointers and array
int arr[] = {1, 2, 3};
By default the array name is a pointer that points to the
first address of the array
arr
0x0016
Cout <<
arr ;
// 0x0016
Cout <<
arr[0];
// 1
1
2
3
0x0016
0x0017
0x0018
Pointers and array
int arr[] = {1, 2, 3};
By default the array name is a pointer that points to the
first address of the array
arr
Cout <<
Cout <<
Cout <<
// 0x0016
arr ;
*arr ;
arr[0];
// 1
int *ptr = arr;
Cout << ptr[1];
// 2
// 1
0x0016
1
2
3
0x0016
0x0017
0x0018
playing with Pointers and array
Pointer Arithmetics
int arr[] = {1, 2, 3};
int *ptr = arr;
Cout << ( ptr+1 );
// 7
Cout << ( ptr+2 );
// 8
5
0x0016
prt
Note :
>> the number we add to ptr is not a value it’s a unit
>> don’t forget the brackets ( )
7
8
0x0017
Prt+1
0x0018
Prt+2
More playing 😂 with Pointers and array
Pointer Arithmetic
int arr[] = {1, 2, 3};
int *ptr = arr;
Ptr += 2;
// ptr = ptr + 2
Cout << *ptr ;
// 8
5
0x0016
prt
7
8
0x0017
Prt+1
0x0018
Prt+2
More playing 😂 with Pointers and array
Pointer Arithmetic
int arr[] = {1, 2, 3};
int *ptr = arr;
Ptr += 2;
Cout << ptr - arr ;
Cout << *( ptr - arr );
5
0x0016
prt
// ptr = ptr + 2
// 2
// ERROR
7
8
0x0017
Prt+1
0x0018
Prt+2
More playing 😂 with Pointers and array
Pointer Arithmetic
int arr[] = {1, 2, 3};
int *ptr = arr;
Cout << *( ptr++ );
Cout << *( ++ptr );
// 5
// 6
// 7
5
0x0016
prt
Cout << ++( *ptr );
7
8
0x0017
Prt+1
0x0018
Prt+2
Common errors while using pointers
>> Uninitialized pointers
❌
Int *ptr;
*ptr = 56;
✅
Int num;
Int *ptr =&num;
*ptr = 56;
int *q,*p;
p = q;
*p = 25;
int *q = &num,*p;
p = q;
*p = 25;
Common errors while using pointers
>> Uninitialized pointers
❌
Int *ptr;
*ptr = 56;
✅
Int num;
Int *ptr =&num;
*ptr = 56;
int *q,*p;
p = q;
*p = 25;
int *q = &num,*p;
p = q;
*p = 25;
Common errors while using pointers
>> NULL pointer direct usage
❌
Int *ptr = 0;
*ptr = 56;
✅
Int *ptr = 0;
Int num;
Int *ptr =&num;
*ptr = 56;
Structures
Structures (also called structs) are a way to group several related
variables into one place. Each variable in the structure is known as a
member of the structure.
Unlike an array, a structure can contain many different data types (int,
string, bool, etc.).
To create a structure, use the struct keyword and declare each of its
members inside curly braces.
classes
A class is a user-defined data type that we can use in our program, and
it works as an object constructor, or a "blueprint" for creating objects.
To create a class, use the class keyword
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