1. Lecture 8 of Computer Science II Recursions Instructor: Mr.Ahmed Al Astal

2.  Page 2 Recursions  Recursion is a programming technique in which a method (function) calls itself.  Recursion is another way to achieve repetition, which occurs when a function calls itself.

3.  Page 3 Recursions The Factorial function  let us begin with a simple example of computing the value of the factorial function.

4.  Page 4 Recursions The Factorial function  In general, for a positive integer n, we can define factorial(n) to be n·factorial(n − 1).

5.  Page 5 Recursions A Recursive Implementation of the Factorial Function  let us begin with a simple example of computing the value of the factorial function.

6.  Page 6 Recursions Advantage of using recursion?  What is the advantage of using recursion?  For some problems, however, a recursive implementation can be significantly simpler and easier to understand than an iterative implementation.  Such an example is Drawing an English Ruler.

7.  Page 7 Recursions Drawing an English Ruler ! Three sample outputs of the ruler-drawing function: (a)a 2-inch ruler with major tick length 4; (b) (b) a 1-inch ruler with major tick length 5; (c) (c) a 3-inch ruler with major tick length 3.

8.  Page 8 Recursions A Recursive Approach to Ruler Drawing consists of three functions.:  The main function drawRuler(): draws the entire ruler. Its arguments are the total number of inches in the ruler, nInches, and the major tick length, majorLength.  The utility function drawOneTick(): draws a single tick of the given length. It can also be given an optional integer label, which is printed if it is nonnegative.  The recursive function drawTicks(): which draws the sequence of ticks within some interval. Its only argument is the tick length associated with the interval's central tick.

9.  Page 9 Recursions A recursive implementation