Why Arrays Exist and What Problem They Solve in DSA Rust - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an array of 5 integers in Rust.

DSA Rust

let numbers: [i32; 5] = [1];

Drag options to blanks, or click blank then click option'

A(1, 2, 3, 4, 5)

B<1, 2, 3, 4, 5>

C{1, 2, 3, 4, 5}

D[1, 2, 3, 4, 5]

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses instead of square brackets.

Using curly braces or angle brackets instead of square brackets.

Arrays in Rust use square brackets to hold elements. So [1, 2, 3, 4, 5] is the correct syntax.

2fill in blank

medium

Complete the code to access the third element of the array named numbers.

DSA Rust

let third = numbers[1];

Drag options to blanks, or click blank then click option'

A[2]

B(2)

C{2}

D<2>

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses or curly braces for indexing.

Using index 3 instead of 2 for the third element.

Arrays in Rust are accessed using square brackets with zero-based indexing. So numbers[2] gets the third element.

3fill in blank

hard

Fix the error in the code to create an array of 4 zeros.

DSA Rust

let zeros = [0; [1]];

Drag options to blanks, or click blank then click option'

A4

B3

C5

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong count number.

Using zero as the count, which creates an empty array.

The syntax [value; count] creates an array with count copies of value. To create 4 zeros, use [0; 4].

4fill in blank

hard

Fill both blanks to create an array of 3 strings and access the first element.

DSA Rust

let fruits: [&str; [1]] = ["apple", "banana", "cherry"];
let first = fruits[2];

Drag options to blanks, or click blank then click option'

A3

B2

C[0]

D(0)

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong size for the array.

Using parentheses instead of square brackets for indexing.

The array has 3 elements, so the size is 3. To access the first element, use square brackets with index 0: fruits[0].

5fill in blank

hard

Fill both blanks to create a function that returns the length of an array of integers.

DSA Rust

fn array_length(arr: &[i32; [1]]) -> usize {
    arr[2]len()
}

Drag options to blanks, or click blank then click option'

A5

B.

D->

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the dot before len().

Adding extra symbols after len().

Using the wrong array size.

The function takes a reference to an array of size 5. To call the len() method, use dot notation arr.len(). The function returns the length directly, so no extra symbol is needed after len().

Practice

1. Why do arrays exist in programming languages like Rust?

easy

A. To store multiple values of the same type in a fixed-size, ordered collection

B. To store values of different types without any order

C. To perform mathematical calculations faster than variables

D. To replace functions with data

Solution

1. Step 1: Understand array purpose and properties

   Arrays are designed to hold multiple values of the same type in a fixed-size, ordered collection, unlike other structures.

2. Final Answer:

   To store multiple values of the same type in a fixed-size, ordered collection -> Option A

3. Quick Check:

   Arrays = fixed-size, same type, ordered [OK]

Hint: Arrays hold same-type items in order with fixed size [OK]

Common Mistakes:

• Thinking arrays can hold different types
• Confusing arrays with lists or sets
• Assuming arrays are dynamic in size

2. Which of the following is the correct way to declare an array of 5 integers in Rust?

easy

A. let arr = <1, 2, 3, 4, 5>;

B. let arr = (1, 2, 3, 4, 5);

C. let arr = [1, 2, 3, 4, 5];

D. let arr = {1, 2, 3, 4, 5};

Solution

1. Step 1: Recall Rust array syntax and check options

   Rust arrays use square brackets [] with values. let arr = [1, 2, 3, 4, 5]; correct; ()=tuple, {}=invalid, <=invalid.

2. Final Answer:

   let arr = [1, 2, 3, 4, 5]; -> Option C

3. Quick Check:

   Rust arrays use [] brackets [OK]

Hint: Use square brackets [] for arrays in Rust [OK]

Common Mistakes:

• Using parentheses () which create tuples
• Using braces {} which are for blocks or sets in other languages
• Using angle brackets <> which are invalid here

3. What will be the output of this Rust code?

let arr = [10, 20, 30, 40, 50];
println!("{}", arr[2]);

easy

A. Index out of bounds error

B. 20

C. 40

D. 30

Solution

1. Step 1: Trace zero-based array indexing

   Rust arrays zero-indexed: arr[0]=10, arr[1]=20, arr[2]=30. println! prints arr[2] = 30.

2. Final Answer:

   30 -> Option D

3. Quick Check:

   arr[2] = 30 [OK]

Hint: Remember Rust arrays start at index 0 [OK]

Common Mistakes:

• Thinking arrays are 1-indexed so arr[2] = 20
• Expecting 40 instead of 30
• Thinking Rust arrays start at 1

4. Identify the error in this Rust code that tries to create an array and print its length:

let arr = [1, 2, 3, 4];
println!("Length: {}", arr.len);

medium

A. Array declaration syntax is wrong

B. Missing parentheses after len method call

C. println! macro is used incorrectly

D. Arrays do not have a length property

Solution

1. Step 1: Check array length method usage

   Rust arrays use len() method with parentheses. Code has arr.len (no ()), causing syntax error.

2. Final Answer:

   Missing parentheses after len method call -> Option B

3. Quick Check:

   Use arr.len() to get length [OK]

Hint: Call len() with parentheses to get array length [OK]

Common Mistakes:

• Using arr.len without ()
• Confusing array length with size property
• Trying to print length without format string

5. You want to store the daily temperatures for a week using an array in Rust. Which problem does using an array solve best in this case?

medium

A. It provides a fixed-size, ordered collection to access temperatures by day index efficiently

B. It allows storing temperatures of different types like integers and strings together

C. It automatically resizes when more days are added

D. It sorts the temperatures automatically

Solution

1. Step 1: Match array properties to use case

   Fixed 7 days: array fixed-size, ordered, efficient index access. Not mixed types, no auto-resize (Vec for that), no auto-sort.

2. Final Answer:

   It provides a fixed-size, ordered collection to access temperatures by day index efficiently -> Option A

3. Quick Check:

   Arrays = fixed size + order + fast access [OK]

Hint: Arrays store fixed-size ordered data for quick index access [OK]

Common Mistakes:

• Thinking arrays can hold mixed types
• Expecting automatic resizing
• Assuming arrays sort data automatically