BASH/C3/Recursive-function/English

Title of script: Advance topics in function

Author: Lavitha Pereira

Keywords: Video tutorial, recursive function

Visual Cue	Narration
Display Slide 1	Dear friends, welcome to the spoken tutorial on Recursive function.
Display Slide 2	In this tutorial, we will learn What is a Recursive function? With the help of some examples
Display Slide 3Prerequisites	To follow this tutorial, you should have knowledge of Shell Scripting in BASH. If not, for relevant tutorials please visit our website which is as shown,(http://www.spoken-tutorial.org)
Display Slide 4 System requirements	For this tutorial I am using Ubuntu Linux 12.04 Operating System and GNU BASH version 4.2 Please note, GNU Bash version 4 or above is recommended to practice this tutorial.
Display slide 8 Recursion	Let us see what a recursive function is. A recursive function is one which calls itself Recursion is a useful technique for simplifying complex algorithms
	Let me open a file named factorial.sh
Highlight #!/usr/bin/env bash	I have typed some code in this file. This is the shebang line.
factorial() { }	factorial is the function name. and it is an empty function.
factorial() { echo "We are inside a factorial function" }	Let's write a line of code that will print a message “We are inside a factorial function”
#main script read -p "Enter the number:" n	This statement reads user's input and stores the value in variable 'n'
if [ $n -eq 0 ]; then echo "factorial value of $n is 1"	Here I have an if-else condition. If condition checks whether the value of 'n' is equal to zero. If true, it will display the message "factorial value of 0 is 1".
else #calling factorial function factorial $n fi	Here is the else part of the if statement. It calls the factorial function. And fi is the end of the if-else statement.
Switch to terminal	Let us run the file factorial.sh. Open the terminal using CTRL+ALT+T keys simultaneously on your keyboard.
Type chmod +x factorial.sh>>Press Enter dot slash factorial.sh	Type:chmod space plus x space factorial dot sh Press Enter. Type dot slash factorial.sh Press Enter.
Type:0	I will enter 0 and press Enter.
Highlight Output	We see the output as: factorial value of 0 is 1
dot slash factorial.sh Type: 5	Now press the uparrow key. Recall the previous command. Press Enter. This time, I will enter 5 and press Enter.
Highlight Output	The output is: We are inside a factorial function.
	Now let us add some more logic to the factorial function. We will calculate the factorial of a number. Come back to our code.
Type: temp=$1 if [ $temp -eq 1 ]; then echo "1" else f=$((temp-1)) #Recursive call f=$(factorial $f) f=$((f*temp)) echo $f fi	Now let us replace, the echo statement inside the factorial function with the code block. Click on Save
temp=$1	temp is a variable and stores the value entered by user.
if [ $temp -eq 1 ]; then echo “1”	If condition checks whether the variable value is equal to 1. If true, it will prints 1.
else f=$((temp-1))	This is the else part of the if statement. This reduces one from the temp variable value. And stores the result in a variable 'f'.
#Recursive call f=$(factorial $f)	Variable f stores the output of factorial function. This is a recursive call.
f=$((f*temp)) echo $f	Value of variable f and temp is multiplied and stored in f. Then we print the vaue of f.
fi }	End of if-else statement and function.
	Save the file and come to the slides. Let us understand the flow of the program.
Workflow of Program <<Flowchart>>	# The value of n is taken from the user ie n If the value entered is equal to zero then it prints a message Else it goes to the function factorial Here, if the value is equal to one then it prints value as one If not, it makes a recursive call until the value is equal to one Then, all the values are multiplied and displayed
[Highlight] ./factorial.sh Press Enter	Now come back to the terminal. Press the uparrow key. Recall the previous command. ./factorial.sh Press Enter. Now I will enter 5 as the input value.
Output	We get the factorial of number 5. ie 120.
Terminal [Output]	We can see the flow of the program on terminal. Analyse and trace the flow of program. Come back to our slides.
Display Slide 10 Summary	Let us summarise. In this tutorial we have learnt, Recursive function With the help of some examples
Display Slide 10 Assignment	As an assignment. Write a program, where the recursive function calculates the sum of N numbers
Display Slide 11 http://spoken-tutorial.org /What\_is\_a\_Spoken\_Tutorial About the Spoken Tutorial Project	Watch the video available at the link shown below. It summarises the Spoken Tutorial project. If you do not have good bandwidth, you can download and watch it.
Display Slide 12 Spoken Tutorial Workshops	The Spoken Tutorial Project Team Conducts workshops using spoken tutorials Gives certificates to those who pass an online test For more details, please write to contact@spoken-tutorial.org
Display Slide 13 Acknowledgement	Spoken Tutorial Project is a part of the Talk to a Teacher project. It is supported by the National Mission on Education through ICT, MHRD, Government of India. More information on this Mission is available at: http://spoken-tutorial.org\NMEICT-Intro
Display Slide 14	The script has been contributed by FOSSEE and Spoken-Tutorial teams. This is Ashwini from IIT Bombay. Thank you for joining.

Contributors and Content Editors

Ashwini, Nancyvarkey