View source for Rust/C2/Variables-and-Mutability-in-Rust/English

Title of the script: Variables and Mutability

Author: Jayesh Katta Ramalingaiah

Domain Reviewer: 

Novice Reviewer: Praveen S

Keywords: Rust, cargo, package manager, variables, mut



{| border = “1”
|| <center>'''Visual Cue'''</center>
|| <center>'''Narration'''</center>

|-
|| Slide: Title
|| Welcome to the spoken tutorial on “'''Variables and Mutability in RUST'''”.

|-
|| Slide: 

Learning Objectives
|| In this tutorial, we will learn:

* How to create '''variables'''.
* About '''mutability''' and 
* How to '''mutate variables''' in '''Rust'''

|-
|| Slide: System Specifications
|| This tutorial is recorded using:

* '''Ubuntu Linux''' OS version 18.04
* '''Rust''' version 1.47.0
* '''Visual Studio Code''' version 1.45.0 ('''code editor''')

However you may use any other '''editor''' of your choice.

|-
|| Slide : Pre-requisites
|| To practice this tutorial,

* You should be familiar with '''compiling''' and '''running Rust''' files'''.'''
* If not, please go through the prerequisite '''Rust''' tutorials on this website.

|-
|| Slide: Code files
|| 
* The files used in this tutorial are available in the''' Code files''' link on this tutorial page.
* Pls download and extract the file.
* Make a copy and then use it for practising.

|-
|| Slide: Mutability
|| 
* In '''Rust, variables''' are '''immutable''' by default. 
* That means, once the '''variable''' is '''declared''' we cannot change its value. 
* This is one of many advantages in '''Rust '''
* That encourages us to write our code in a way that,
* It takes advantage of the safety and concurrency that '''Rust''' offers.

To understand this let us create a '''project''' and see how this works.

|-
|| Press '''Ctrl+Alt+T '''keys
|| Open the '''terminal''' by pressing '''Ctrl,Alt''' and '''T''' keys simultaneously on the keyboard.


Ensure that you have '''root permissions''' to '''run''' the '''commands'''.

|-
|| Only Narration
|| Here onwards, please remember to press the '''Enter''' key after typing each '''command'''.

|-
|| <nowiki>[Terminal] Type:</nowiki>


cd Desktop/MyRustProject

<nowiki>[Enter]</nowiki>
|| Using '''cd''' command go to the '''Rust''' practice folder which we created earlier.

|-
|| <nowiki>[Terminal] Type:</nowiki>


<nowiki>cargo new variables_mutability [Enter]</nowiki>
|| Let us create a new '''project''' named '''new variables_mutability.'''


Type the '''command''' as shown.

|-
|| Open Visual Studio Code editor.
|| You may use any '''editor''' of your choice.


I will use '''Visual Studio Code editor '''for this demonstration'''.'''

|-
|| <nowiki>[Editor] </nowiki>


Welcome Page ->

Open Folder ->

variables_mutability
|| Open the created '''project''' by clicking on the '''Open folder''' link in the '''Welcome page.'''


Browse and locate the  “'''variables_mutability'''” folder.


Then click on the '''OK '''button at the top right corner.

|-
|| <nowiki>[Editor] </nowiki>

Click on '''variables_mutability'''
|| Under '''EXPLORER''' section, expand the '''project  “variables_mutability'''” by clicking on it.

|-
|| <nowiki>[Editor] </nowiki>Expand '''src '''and click on '''main.rs'''
|| Then expand the '''src''' and open the '''main.rs''' file.

|-
|| <nowiki>[Editor] Type: </nowiki>


fn main(){

let a = 1;

print!(“The value of a is {}”,a);

a=2;

print!(“The value of a is {}”,a);

}
|| In the '''editor''', replace the '''code''' as shown.

|-
|| <nowiki>[Editor] </nowiki>

Highlight: '''let '''
|| '''let keyword''' is used to '''declare variables''' in '''Rust.'''

|-
|| <nowiki>[Editor] Highlight: </nowiki>


'''let a = 1;'''
|| Here we have '''initialized''' the '''variable a '''and assigned the value '''1''' to it.

|-
|| <nowiki>[Editor] Highlight:</nowiki>


'''println!("The value of a is {}",a);'''
|| Using the '''println macro''' we are printing the value.

|-
|| <nowiki>[Editor] Highlight:</nowiki>


print!("The value of a is '''{}'''",a);
|| Here the '''{} open and close brace'''is a '''format specifier.'''

|-
|| <nowiki>[Editor] Highlight:</nowiki>


print!("The value of a is {}",'''a''');
|| In the '''print method''', the '''variable a''' is after comma.


It is the value for the respective '''format specifier'''.

|-
|| <nowiki>[Editor] Highlight:</nowiki>


'''a = 2;'''
|| Here, we are trying to reassign the '''variable''' to 2.

|-
|| <nowiki>[Editor] Highlight:</nowiki>


'''print!("The value of a is {}",a);'''
|| After reassigning we are printing the '''variable’s''' value to see what does the value contain.

|-
|| Ctrl + S
|| Save the file.

|-
|| Switch to terminal
|| Switch back to the '''terminal.'''

|-
|| <nowiki>[Terminal] Type: </nowiki>


cd '''variables_mutability'''

<nowiki>[Enter]</nowiki>
|| Go to the '''project''' folder '''variables_mutability '''using the '''cd command.'''

|-
|| <nowiki>[Terminal] Type: </nowiki>


'''cargo build '''<nowiki>[Enter]</nowiki>
|| To '''compile '''the '''Cargo project''', type '''cargo build'''.

|-
|| <nowiki>[Terminal] Highlight: </nowiki>


'''cannot assign twice to immutable variable ‘a’'''
|| Here, we can see an error - '''cannot assign twice to immutable variable ‘a’.'''


Recall in the beginning of the tutorial I had mentioned that''' variables''' are '''immutable''' by default.

|-
|| Switch to Editor
|| So switch back to the '''editor.'''

|-
|| <nowiki>[Editor] Type:</nowiki>

let''' mut '''a = 1;
|| Now, type '''m u t '''in between '''let''' and '''a'''. 


|-
|| <nowiki>[Editor] Highlight:</nowiki>

let''' mut '''a = 1;
|| Here we are telling the '''compiler''' that the '''initialized variable''' is '''mutable'''.

|-
|| Ctrl + S
|| Save the file.

|-
|| Switch to terminal
|| Switch back to the '''terminal.'''

|-
|| <nowiki>[Terminal] Type: </nowiki>


<nowiki>cargo run [Enter]</nowiki>
|| Now type '''cargo run'''

|-
|| <nowiki>[Terminal] Highlight</nowiki>


The value of a is 1The value of a is 2
|| We can see the output. 


Both the '''initialized''' and the modified values are printed successfully.

|-
|| <nowiki>[Terminal] Highlight: </nowiki>


cargo run 
|| After switching back, I directly did a '''cargo run''' without '''compiling''' the '''project''' again.


Did you notice that?


When we do a''' cargo run''' the '''package manager''' will '''build''' again and '''run''' the '''project'''. 


So going forward, we can directly use '''cargo run''' to '''build '''and '''run '''the '''project''' in one go.

|-
|| Only narration
|| With this we have come to the end of this tutorial. 


Let’s summarize.

|-
|| Slide''': '''Summary''' '''
|| In this tutorial, we have learnt:

* How to create '''variables'''
* About '''mutability''' and
* How to '''mutate variables'''

|-
|| Slide: Assignment
|| As an assignment,

* Go to the '''project''' folder '''rust-assignment'''
* In the '''main.rs''' file
** Create a '''variable '''named '''s''' and make it '''mutable'''.
** Assign '''13''' as a value to '''s''' 
** Print the value of '''s'''
** Reassign the value of '''s''' as '''19'''
** Print the value of '''s'''
* '''Compile '''and '''execute '''the '''project'''.
* Observe the output in the '''Terminal'''

|-
|| '''Slide: '''About Spoken Tutorial Project
|| 
* The video at the following link summarises the Spoken Tutorial project.
* Please download and watch it

|-
|| '''Slide:''' Spoken tutorial workshops
|| 
* We conduct workshops using spoken tutorials and give certificates.
* For more details, please write to us.

|-
|| Slide: Forum questions
|| Pls post your timed queries in this forum

|-
|| Slide: Acknowledgement
|| Spoken Tutorial Project is funded by Ministry of Education, Government of India

|-
|| Slide: Thanks
|| This is Jayesh signing off. Thank you for joining

|}