Vector creation in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new empty vector.

Rust

let v = Vec::[1]();

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

Alen

Bwith_capacity

Cpush

Dnew

Attempts:

3 left

💡 Hint

Common Mistakes

Using push instead of new to create a vector.

Trying to use len() which returns size, not creates vector.

The Vec::new() function creates a new empty vector.

2fill in blank

medium

Complete the code to create a vector with capacity for 10 elements.

Rust

let v = Vec::[1](10);

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

Awith_capacity

Bnew

Cpush

Dreserve

Attempts:

3 left

💡 Hint

Common Mistakes

Using new() which creates an empty vector with zero capacity.

Using reserve() which is a method, not a constructor.

The Vec::with_capacity(10) creates a vector with space for 10 elements.

3fill in blank

hard

Fix the error in the code to create a vector with initial elements.

Rust

let v = vec![1]1, 2, 3[1];

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

A[ ]

B( )

C{ }

D< >

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses or braces instead of square brackets.

Omitting brackets entirely.

The vec! macro requires square brackets around the elements.

4fill in blank

hard

Fill both blanks to create a vector of integers from 1 to 5.

Rust

let v: Vec<i32> = ([1]..[2]).collect();

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

A1

B6

C5

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1..5 which excludes 5.

Using 0..5 which starts from zero.

The range 1..6 includes 1 up to but not including 6, so it covers 1 to 5.

5fill in blank

hard

Fill all three blanks to create a vector of squares of numbers 1 to 4.

Rust

let v = (1..[1]).map(|[2]| [2] * [3]).collect::<Vec<i32>>();

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

A5

Bx

D4

Attempts:

3 left

💡 Hint

Common Mistakes

Using 4 as upper bound excludes 4.

Using different variable names in closure parameters and body.

The range 1..5 covers 1 to 4. The variable x is used in the closure to square each number.

Practice

1. Which of the following correctly creates an empty vector of integers in Rust?

easy

A. let v: Vec<i32> = Vec::new();

B. let v = vec!();

C. let v = Vector::new();

D. let v = vec![0];

Solution

1. Step 1: Understand how to create an empty vector

   In Rust, an empty vector is created using Vec::new() with the type specified if needed.

2. Step 2: Check each option

   let v: Vec<i32> = Vec::new(); uses Vec::new() with type i32, which is correct. let v = vec!(); uses vec!() which is invalid syntax. let v = Vector::new(); uses Vector::new() which is not a Rust type. let v = vec![0]; creates a vector with one element 0, not empty.

3. Final Answer:

   let v: Vec<i32> = Vec::new(); -> Option A

4. Quick Check:

   Empty vector = Vec::new() [OK]

Hint: Empty vector uses Vec::new() with type [OK]

Common Mistakes:

• Using vec!() with empty parentheses
• Using Vector instead of Vec
• Creating vector with one element instead of empty

2. Which syntax correctly creates a vector with the values 1, 2, and 3 in Rust?

easy

A. let v = vec{1, 2, 3};

B. let v = Vec[1, 2, 3];

C. let v = vec(1, 2, 3);

D. let v = vec![1, 2, 3];

Solution

1. Step 1: Recall vector creation with values

   Rust uses the macro vec![...] with square brackets and exclamation mark to create vectors with initial values.

2. Step 2: Evaluate each option

   let v = vec![1, 2, 3]; uses correct syntax vec![1, 2, 3]. let v = Vec[1, 2, 3]; uses square brackets without exclamation mark, invalid. let v = vec(1, 2, 3); uses parentheses, invalid. let v = vec{1, 2, 3}; uses curly braces, invalid.

3. Final Answer:

   let v = vec![1, 2, 3]; -> Option D

4. Quick Check:

   Vector with values = vec![...] [OK]

Hint: Use vec! macro with square brackets for values [OK]

Common Mistakes:

• Missing exclamation mark after vec
• Using parentheses or curly braces instead of brackets
• Using Vec[...] which is invalid syntax

3. What is the output of this Rust code?

let mut v = Vec::new();
v.push(10);
v.push(20);
println!("{:?}", v);

medium

A. [10, 20]

B. [20, 10]

C. 10 20

D. Error: cannot push to vector

Solution

1. Step 1: Understand vector push operations

   The vector starts empty. push(10) adds 10 at the end, then push(20) adds 20 after 10.

2. Step 2: Check the printed output

   The println!("{:?}", v) prints the vector in debug format showing all elements in order: [10, 20].

3. Final Answer:

   [10, 20] -> Option A

4. Quick Check:

   Push adds elements in order [OK]

Hint: push adds elements at the end, print shows all [OK]

Common Mistakes:

• Assuming push adds at the front
• Printing vector without debug format
• Confusing order of elements

4. Identify the error in this Rust code snippet:

let v = Vec::new();
v.push(5);

medium

A. push method does not exist for vectors

B. Vec::new() does not create a vector

C. Cannot push to an immutable vector

D. Missing semicolon after Vec::new()

Solution

1. Step 1: Check vector mutability

   The vector v is declared without mut, so it is immutable by default.

2. Step 2: Understand push method requirements

   The push method requires the vector to be mutable to add elements. Trying to push to an immutable vector causes a compile error.

3. Final Answer:

   Cannot push to an immutable vector -> Option C

4. Quick Check:

   push needs mutable vector [OK]

Hint: Add mut to vector to allow push [OK]

Common Mistakes:

• Forgetting mut keyword
• Thinking Vec::new() returns non-vector
• Assuming push works on immutable vectors

5. You want to create a vector of strings from an array of &str slices and then add a new string. Which code correctly does this?

hard

A. let v = vec!["a", "b", "c"]; v.push("d");

B. let mut v: Vec<String> = ["a", "b", "c"].iter().map(|&s| s.to_string()).collect(); v.push("d".to_string());

C. let mut v = Vec::new(); v.push(["a", "b", "c"]); v.push("d");

D. let mut v = vec![String::from("a"), String::from("b"), String::from("c")]; v.push('d');

Solution

1. Step 1: Convert &str slices to String vector

   The array of &str slices needs to be converted to a vector of String using iter(), map() with to_string(), then collect().

2. Step 2: Add a new String element

   After creating a mutable vector, use push with "d".to_string() to add a new string.

3. Step 3: Check other options

   let v = vec!["a", "b", "c"]; v.push("d"); tries to push to an immutable vector of &str slices, invalid. let mut v = Vec::new(); v.push(["a", "b", "c"]); v.push("d"); tries to push an array inside vector, invalid. let mut v = vec![String::from("a"), String::from("b"), String::from("c")]; v.push('d'); pushes a char instead of String, invalid.

4. Final Answer:

   let mut v: Vec<String> = ["a", "b", "c"].iter().map(|&s| s.to_string()).collect(); v.push("d".to_string()); -> Option B

5. Quick Check:

   Convert slices to String vector, then push String [OK]

Hint: Map &str to String, collect to Vec<String>, then push [OK]

Common Mistakes:

• Trying to push to immutable vector
• Pushing wrong types (char instead of String)
• Not converting &str slices to String