String slices in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a string slice from the variable text.

Rust

let text = String::from("hello world");
let slice = &text[1];
println!("{}", slice);

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

A[..5]

B[1..4]

C[..]

D[5..]

Attempts:

3 left

💡 Hint

Common Mistakes

Using an index that causes a runtime error.

Forgetting the & to create a reference.

The &text[..] syntax creates a slice of the entire string.

2fill in blank

medium

Complete the code to get a slice of the first 5 characters from text.

Rust

let text = String::from("hello world");
let slice = &text[1];
println!("{}", slice);

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

A[..5]

B[6..11]

C[1..6]

D[5..]

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect range indices.

Forgetting that the end index is exclusive.

The slice &text[..5] gets the first 5 characters.

3fill in blank

hard

Fix the error in the code to correctly slice the string from index 6 to the end.

Rust

let text = String::from("hello world");
let slice = &text[1];
println!("{}", slice);

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

A[6..]

B[..6]

C[6]

D[..]

Attempts:

3 left

💡 Hint

Common Mistakes

Using a single index without range brackets.

Using the wrong range direction.

The correct slice from index 6 to the end is &text[6..].

4fill in blank

hard

Fill both blanks to create a slice of text from index 2 to 7.

Rust

let text = String::from("rustacean");
let slice = &text[1][2];
println!("{}", slice);

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

A[2..

B7]

C[3..

D6]

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up start and end indices.

Forgetting to close the slice brackets properly.

The slice syntax is &text[2..7] to get characters from index 2 up to but not including 7.

5fill in blank

hard

Fill all three blanks to create a slice of text from index 1 to 4 and print its length.

Rust

let text = String::from("example");
let slice = &text[1][2][3];
println!("Length: {}", slice.len());

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

A[1

B..

C4]

D[..4]

Attempts:

3 left

💡 Hint

Common Mistakes

Using incomplete slice syntax.

Forgetting the range operator between indices.

The slice &text[1..4] gets characters from index 1 up to 4. The length is printed with slice.len().

Practice

1. What is a string slice in Rust?

easy

A. A type of integer used for indexing strings

B. A reference to a part of a string without copying it

C. A function that modifies a string in place

D. A new string created by copying characters

Solution

1. Step 1: Understand string slice concept

   A string slice is a reference to a part of a string, not a new string.

2. Step 2: Compare options

   Only A reference to a part of a string without copying it describes a reference without copying, which matches string slices.

3. Final Answer:

   A reference to a part of a string without copying it -> Option B

4. Quick Check:

   String slice = reference without copy [OK]

Hint: Remember: slices borrow, not copy strings [OK]

Common Mistakes:

• Thinking slices create new strings
• Confusing slices with string modification
• Believing slices are integer types

2. Which of the following is the correct syntax to get a slice of the first 4 characters from a string text?

easy

A. &text[0..4]

B. text.slice(0, 4)

C. &text[1..5]

D. text[0:4]

Solution

1. Step 1: Recall Rust slice syntax

   Rust uses &string[start..end] to get a slice from start to end-1.

2. Step 2: Check options

   &text[0..4] uses &text[0..4], which correctly slices first 4 chars (indices 0 to 3).

3. Final Answer:

   &text[0..4] -> Option A

4. Quick Check:

   Slice syntax = &string[start..end] [OK]

Hint: Use &string[start..end] for slices, not methods or colons [OK]

Common Mistakes:

• Using method calls like slice() which don't exist
• Using 1-based indexing instead of 0-based
• Using Python-style slicing with colons

3. What will the following Rust code print?

let s = String::from("hello world");
let slice = &s[6..11];
println!("{}", slice);

medium

A. hello

B. Syntax error

C. hello world

D. world

Solution

1. Step 1: Understand slicing indices

   The slice &s[6..11] takes characters from index 6 up to 10 (11 excluded).

2. Step 2: Identify substring

   In "hello world", index 6 is 'w' and index 10 is 'd', so slice is "world".

3. Final Answer:

   world -> Option D

4. Quick Check:

   Slice &s[6..11] = "world" [OK]

Hint: Remember slice end index is excluded [OK]

Common Mistakes:

• Including the end index character
• Confusing start and end indices
• Expecting full string output

4. Identify the error in this Rust code snippet:

let s = String::from("rustacean");
let slice = &s[0..5];
println!("{}", slice);
let invalid_slice = &s[5..15];

medium

A. The slice &s[5..15] causes a runtime panic due to out-of-bounds

B. The slice &s[0..5] is invalid syntax

C. The println! macro is missing a semicolon

D. String::from cannot create strings with length 9

Solution

1. Step 1: Check slice ranges

   The string "rustacean" has length 9, so valid indices are 0 to 8.

2. Step 2: Analyze invalid slice

   The slice &s[5..15] tries to access indices beyond length, causing runtime panic.

3. Final Answer:

   The slice &s[5..15] causes a runtime panic due to out-of-bounds -> Option A

4. Quick Check:

   Out-of-bounds slice = panic [OK]

Hint: Slice end must be ≤ string length to avoid panic [OK]

Common Mistakes:

• Assuming slices auto-adjust to string length
• Thinking &s[0..5] is invalid syntax
• Ignoring runtime panics from invalid slices

5. Given a string text, how can you safely get a slice of the first n characters without risking a runtime panic if n is larger than the string length?

hard

A. Use text.get(0..n).unwrap()

B. Use &text[0..n] without checks

C. Use &text[0..n.min(text.len())]

D. Use &text[0..=n]

Solution

1. Step 1: Understand safe slicing

   To avoid panic, slice end must not exceed string length.

2. Step 2: Use min to limit slice end

   Using n.min(text.len()) ensures slice end is at most string length.

3. Final Answer:

   Use &text[0..n.min(text.len())] -> Option C

4. Quick Check:

   Safe slice end = min(n, length) [OK]

Hint: Use min() to limit slice end safely [OK]

Common Mistakes:

• Slicing without length check causing panic
• Using unwrap() which can panic if None
• Using inclusive range which is invalid for slices