Introduction To Programming Information Technology , 1’ st Semester

1. MINISTRY OF EDUCATION & HIGHER EDUCATION COLLEGE OF SCIENCE AND TECHNOLOGY KHANYOUNIS- PALESTINE Using Java Introduction To ProgrammingInformation Technology , 1’st Semester Lecture 18 Recursion & Pointers in Java Teacher: Mahmoud Rafeek Alfarra

2. Outline • Recursion Concepts • Example Using Recursion: Factorials • Example Using Recursion: Fibonacci Series • Recursion vs. Iteration • What is Pointers ? • Emank X Mezank Presented & Prepared by: Mahmoud R. Alfarra

3. Recursion Concepts • A recursive method is a method that calls itself. • A recursive method can be called either directly, or indirectly through another method. Method Direct recursion Calls Presented & Prepared by: Mahmoud R. Alfarra

4. Recursion Concepts Calls Recursive Method A Method Indirect recursion Calls • A recursive method may call another method, which may in turn make a call back to the recursive method. • Such a process is known as an indirect recursive call or indirect recursion. Presented & Prepared by: Mahmoud R. Alfarra 4

5. Example: Using Recursion: Factorials write a recursive program to perform a popular mathematical calculation. Consider the factorial of a positive integer n, written n!, which is the product of n * (n-1)*(n-2)*….. *1 With 1! equal to 1 and 0! defined to be 1. For example, 5! is the product 5 · 4 · 3 · 2 · 1, which is equal to 120. Presented & Prepared by: Mahmoud R. Alfarra 5

6. Example: Using Recursion: Factorials HW 18.1 Solve this Problem using Iteration Presented & Prepared by: Mahmoud R. Alfarra

7. Example: Using Recursion: Factorials Calling of factorial method to calculate the factorial of numbers from 0 to 10 Presented & Prepared by: Mahmoud R. Alfarra 7

8. Example: Using Recursion: Factorials Presented & Prepared by: Mahmoud R. Alfarra

9. Example Using Recursion: Fibonacci Series fibonacci(n) = fibonacci (n-1)+ fibonacci (n-2) HW 18.2 Solve this Problem using Iteration The Fibonacci seriesbegins with 0 and 1 and has the property that each subsequent Fibonacci number is the sum of the previous two Fibonacci numbers. Presented & Prepared by: Mahmoud R. Alfarra 9

10. Example Using Recursion: Fibonacci Series Presented & Prepared by: Mahmoud R. Alfarra 10

11. Example Using Recursion: Fibonacci Series Presented & Prepared by: Mahmoud R. Alfarra 11

12. Be care Not providing, in the body of a while statement, an action that eventually causes the condition in the while to become false normally results in a logic error called an infinite loop, in which the loop never terminates. Set a semi colon after the condition results a logic error Presented & Prepared by: Mahmoud R. Alfarra 12

13. Recursion vs. Iteration 13 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

14. 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. Presented & Prepared by: Mahmoud R. Alfarra 14

15. What is Pointers ? 15 A pointer is nothing but a variable that holds the memory address of another type. Presented & Prepared by: Mahmoud R. Alfarra

16. Declaring a Pointer type 16 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 ; • The general form of declaring a pointer type is as shown below Presented & Prepared by: Mahmoud R. Alfarra

17. Emank X Mezank كان النبي صلى الله عليه وسلم إذا سمع الرعد أو رأى البرق يقول: (‏سبحان الذي يسبح الرعد بحمده و الملائكة من خيفته) Presented & Prepared by: Mahmoud R. Alfarra

18. Next… Practices Presented & Prepared by: Mahmoud R. Alfarra