Difference between revisions of "BASH/C3/Recursive-function/English"

• What is a Recursive function?
• With the help of some examples

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System requirements

• 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.

Recursion

• A recursive function is one which calls itself
• Recursion is a useful technique for simplifying complex algorithms

#!/usr/bin/env bash

This is the shebang line.

{

}

echo "Inside factorial function"

}

read -p "Enter the number:" n

echo "factorial value of $n is 1"

If condition checks whether the value of 'n' is equal to zero.

If true, it will display the message "factorial value of n is 1".

#calling factorial function

factorial $n

fi

It calls the factorial function.

And fi is the end of the if-else statement.

Open the terminal using CTRL+ALT+T keys simultaneously on your keyboard.

chmod +x factorial.sh>>Press Enter

dot slash factorial.sh

Press Enter.

Type dot slash factorial.sh

Press Enter.

I will enter 0.

Output

factorial value of 0 is 1

Type:

5

Recall the previous command.

Press Enter.

This time, I will enter 5 .

Output

Inside factorial function.

We will calculate the factorial of a number.

Come back to our code.

temp=$1

if [ $temp -eq 1 ]; then

echo "1"

else

f=$((temp-1))

#Recursive call

f=$(factorial $f)

f=$((f*temp))

echo $f

fi

Click on Save

echo “1”

If true, it will print 1.

f=$((temp-1))

This reduces one from the temp variable value.

And stores the result in a variable 'f'.

f=$(factorial $f)

This is a recursive call.

echo $f

Then we print the value of f.

}

Let us understand the flow of the program.

<<Flowchart>>

1. If the value entered is equal to zero, then it prints a message
2. Else it goes to the function factorial
3. Here, if the value is equal to one, then it prints value as one
4. If not, it makes a recursive call until the value is equal to one
5. Then, all the values are multiplied and displayed

./factorial.sh

Press Enter

Press the uparrow key.

Recall the previous command.

./factorial.sh

Press Enter.

Now I will enter 5 as the input value.

i.e. 120.

[Output]

Analyse and trace the flow of program.

Come back to our slides.

Summary

In this tutorial we have learnt,

• Recursive function
• With the help of some examples

Assignment

Write a program where the recursive function calculates the sum of N numbers

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Acknowledgement

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

This is Ashwini from IIT Bombay.

Thank you for joining.