1. Presented By: Mahmoud Rafeek Alfarra
MINISTRY OF EDUCATION & HIGHER EDUCATION
COLLEGE OF SCIENCE AND TECHNOLOGY
KHANYOUNIS- PALESTINE
DATA STRUCTURE
Using C#
Information Technology , 3’rd Semester
Lecture 5:
Recursion & Pointers
Presented By: Mahmoud Rafeek Alfarra

2. Outline Recursion The factorial Recursion vs. Iteration
Emank X Mezank !!

3. Recursion
A recursive method is a method that calls itself either directly or indirectly through another method.
Recursion is an important topic discussed at length in upper-level computer science courses.
Call
Presented & Prepared by: Mahmoud R. Alfarra

4. The factorial
The factorial of an integer number greater than or equal to 0 can be calculated iteratively (nonrecursively) using for as follows:
HW 5.1
Write a method that performs the factorial using recursion
Presented & Prepared by: Mahmoud R. Alfarra

5. The factorial
Presented & Prepared by: Mahmoud R. Alfarra

6. The factorial If (number is less than or equal 1) Return 1 else6
If (number is less than or equal 1)
Return 1
else
Return number * method(number-1)
HW 5.2
Write a method that performs the factorial using recursion technique
HW 5.3
Case study : The Fibonacci Series
Presented & Prepared by: Mahmoud R. Alfarra

7. Recursion vs. Iteration
Both iteration and recursion are based on a control structure.
Iteration uses a repetition structure (such as for, while or do/while)
Recursion uses a selection structure (such as if, if/else or switch).
Presented & Prepared by: Mahmoud R. Alfarra

8. Recursion vs. Iteration
Both iteration and recursion involve repetition.
Iteration explicitly uses a repetition structure.
Recursion achieves repetition through repeated method calls.
Iteration and recursion each involve a termination test.
HW 5.4
Case study : notes more differences between them
Presented & Prepared by: Mahmoud R. Alfarra

9. What is Pointers ? 9
A pointer is nothing but a variable that holds the memory address of another type.
In C#, pointer can only be declared to hold the memory address of value types and arrays.
Presented & Prepared by: Mahmoud R. Alfarra

10. Declaring a Pointer type 10
The general form of declaring a pointer type is as shown below
type * variable_name; 
Where * is known as the de-reference operator
int *x ;
This Declares a pointer variable x, which can hold the address of an int type. The reference operator (&) can be used to get the memory address of a variable.
int x = 100;
The &x gives the memory address of the variable x, which we can assign to a pointer variable
int *ptr = & x ;
Presented & Prepared by: Mahmoud R. Alfarra

11. Pointers Console.WriteLine((int)ptr) // Displays the memory address11
Console.WriteLine((int)ptr) // Displays the memory address
Console.WriteLine(*ptr) // Displays the value at the memory address.
01011AB10
ptr 78
The value of (*ptr) is 78
But the value of (ptr) is 01011AB10
Presented & Prepared by: Mahmoud R. Alfarra

12. Pointers 12
using System; class MyClass { public void Method() { // code { int x = 10; int y = 20; int *ptr1 = &x; int *ptr2 = &y; Console.WriteLine((int)ptr1); Console.WriteLine((int)ptr2); Console.WriteLine(*ptr1); Console.WriteLine(*ptr2); } } }
Presented & Prepared by: Mahmoud R. Alfarra

13. Emank X Mezank !!
قال رسول الله صلى الله عليه وسلم : ( كلكم يدخل الجنـة إلا من أبى, قالوا و من يأبى يا رسول الله ؟ قال : من أطاعني دخل الجنة و من عصاني فقد أبى) رواه البخاري

14. Next Lecture
Linked List