Difference between revisions of "Rust-Programming-Language/C2/Arrays/English"

Title Slide

Learning Objectives

• Arrays

System Requirements

• Ubuntu Linux OS version 22.04
• Rust version 1.80.0
• Visual Studio Code version 1.19.0

Prerequisites

Code Files

• arraysdemo.rs

• The following code file is required to practise this tutorial.

• This file is provided in the Code Files link of this tutorial page.

Arrays

• Arrays in Rust are collections of values of the same data type and have a fixed size
• Arrays once initialized cannot be resized
• An array declaration allocates sequential memory blocks

> cargo new arraysdemo

In the menu bar, File >> Open folder >> Desktop >> MyRustProject >> arraysdemo

Type the command cargo new arraysdemo and press Enter.

Open the created project as shown.

let arr:[i32;4] = [10,20,30,40];

println!("First element: {}",arr[0]);

println!("Second element: {}", arr[1]);

println!("array size is :{}",arr.len());

}

Press Ctrl+s

The values within the square brackets are array values.

In Rust, an array can store values of any datatype.

To display the value of the nth index in an array, we need to pass the index.

Please note that the array index starts from 0.

Save the program.

Let us execute the code and see the output.

In the terminal, type cargo run.

Point to the output.

In the terminal, type cargo run.

It prints the first element as 10, second element as 20 and array size as 4.

We have 4 values in the array.

Let us try to access a value greater than 4, say 6th element where there is no value.

Add the println statement as shown.

Save the file.

We see an error- index out of bounds.

So, arrays in Rust are different as compared to other programming languages.

This is because they have a fixed length.

fn main(){  

// an array with data type and size

    let mut colors: [&str; 3] = ["black", "blue", "red"];

    println!("Original colors: {:?}", colors);

// change the value of the 3rd element in the array

    colors[2] = "green";

    println!("changed colors = {:?}", colors);

  }

We have declared an array of colors with mut.

Here the data type and size of array are specified.

 We have assigned a new value as “green” to the third element in the array.

As the created array is mutable, it is possible to change the value.

Save the file.

The output shows the Original colors as black, blue, red.

And the changed color values as black, blue, green.

Clear the window and copy and paste the code from the code files.

let arr = [1, 2, 3, 4];

// Output: Is empty: false

println!("Is empty: {}", arr.is_empty());

println!("2nd element: {}", arr.get(1).unwrap()); // 2

println!("First element: {}", arr.first().unwrap()); // 1

println!("Last element: {}", arr.last().unwrap()); // 4

let (left, right) = arr.split_at(2);

println!("Left slice:{:?}, Right slice:{:?}", left, right);

}

is_empty() method checks if the array has any elements.

Here, arr has 4 elements, so the result is false.

We can access an element using the .get() method.

It takes the index value as the parameter. 

The get method returns an Option enum.

.get(1) returns an Option<i32> with the value at index 1, which is 2.

.unwrap() extracts the value (2) from Some.

Likewise,.first() returns Some(1) that is the first element.

.unwrap() extracts 1 from Some(1).

.last() returns the last element as 4

.split_at(2) splits the array at index 2, producing two slices:

• left contains the first two elements: that is [1, 2]
• right contains the remaining elements: that is [3, 4]

Save the program.

We can see the left slice and right slice output.

Summary

In this tutorial, we learn about

Arrays

Let us summarize.

Assignment

[10, 20, 30, 40, 50, 60]

• Declare an array of 6 integers
• Use a loop to print all elements in the array
• Create a slice of the array from index 2 to 4
• Print the slice using {:?}

Thank You