Rust-Programming-Language/C2/Variables-and-Mutability/English

Visual Cue	Narration
Show Slide: Title Slide	Welcome to the Spoken Tutorial on Variables and Mutability in Rust.
Slide 2 Learning Objective	In this tutorial, we will learn about: Variables and Mutability
Slide 3 System Requirements	This tutorial is recorded using Ubuntu Linux OS version 22.04 Rust 1.80.0 Visual Studio Code 1.19.0
Slide 4 Prerequisites	To follow this tutorial, You should be familiar with compiling and running a Rust program
Slide 5 Code Files	The following code file required to practise this tutorial This file is provided in the Code Files link of this tutorial page
Slide 6 Variables let a = 10; //immutable let mut b=15;//mutable	In Rust, we create variables using the let statement. By default, variables are immutable,meaning their values cannot be changed You can make them mutable by using mut.
Open Visual Studio Code editor	Let us open the Visual Studio Code editor.
Open the terminal by pressing Ctrl+Tilde (~) Click on Terminal and select New Terminal.	In the menu bar, click on Terminal and select New Terminal. We can see a terminal window at the bottom.
Type at the prompt: cargo new variables	Go to our working directory MyRustProject as explained earlier. Please refer to the Additional Reading material link of this tutorial. It explains the steps to create and run the project. Type the command cargo new variables and press Enter Open the created project as shown.
Point to main.rs file. Press Ctrl + C to copy Press Ctrl + V to paste	In the main.rs file, copy and paste the code from the codefile.
Highlight the code according to narration fn main(){ let a = 1; println!(“The value of a is {}”,a); a=2; println!(“The value of a is {}”,a); }	let keyword is used to declare variables in Rust. Here we have initialized the variable a and assigned the value 1 to it. We are trying to reassign the value 2 to variable a. After reassigning we are printing the variable’s value to see what the value contains. Press Ctrl and S to save the file.
	In the menu bar, click on Terminal and select New Terminal.
Type Cargo build	In the terminal, type cargo build to compile the Cargo project.
Highlight the error	Here, we can see an error - cannot assign twice to immutable variable ‘a’. Note that we had mentioned variables are immutable by default.
	So switch back to the program.
Type mut Let mut a=1;	Now, type mut in between let and a. Here we are telling the compiler that the initialized variable is mutable.
Type cargo run	Save the file. In the terminal, type cargo run
Highlight the output	We can see the output. Both the initialized and modified values are printed successfully.
	Next let us see the shadowing of variables.
Shadowing	Clear the code window and then copy and paste the code from the code file. Rust allows variable shadowing. Here the variable x is shadowing. Shadowing is to declare a new variable with the same name as a previous variable in the same scope. We can assign a new value to the new variable while the old variable remains unchanged. Save the file.
type cargo run	In the terminal, type cargo run Check the output. It prints the value of x as 5 and 7 as the result of shadowing.
	Next we will see the scope of the variables.
Scope of the variable fn main() { // scope of outer_var variable is inside the main function code block let outer_var = 100; // start of the inner code block { // scope of inner_var variable is only inside this new code block let inner_var = 200; println!("inner_var = {}", inner_var); } // end of the inner code block println!("inner_var = {}", inner_var); println!("outer_var = {}", outer_var); }	Clear the code window. Copy and paste the code from the code file. In this code, observe the declaration of variables outer_var and inner_var. Curly braces { } define the block scope where the variable access becomes restricted to the local. Save the program.
Type cargo run	Let us check the output. Run the program. We can see a compilation error. Here we tried to print the inner_var outside of the inner code block. So the program will give an error. Let us comment the print statement of inner_var in the outer block. Save the program. Run the program again to see the output. We can see the output displayed for outer_var as 100 and inner_var as 200. This shows that any variable outside the braces will have global access.
Slide: Summary	This brings us to the end of this tutorial. Let us summarize.
Slide: Assignment fn main() { let x = 10; // Immutable variable println!("The value of x is: {}", x); x = 20; println!("The new value of x is: {}", x); }	As an assignment, do the following. Run the above program Analyse the error and correct the program.
Thank You We would like to thank Vishal Pokuri from VIT Vellore for content contribution.	Thank you for joining.

Contributors and Content Editors

Madhurig, Nirmala Venkat