Character type in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a character variable with the letter 'a'.

Rust

let letter: char = '[1]';

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

A'a'

B'ab'

Ca

D"a"

Attempts:

3 left

💡 Hint

Common Mistakes

Using double quotes instead of single quotes.

Not using quotes at all.

Using more than one character inside quotes.

In Rust, a character is declared using single quotes around a single character, like 'a'.

2fill in blank

medium

Complete the code to print the Unicode code point of the character 'Z'.

Rust

let ch: char = 'Z';
println!("{}", ch [1] u32);

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

Ato_digit

Bto_ascii_uppercase

Cto_string

Das

Attempts:

3 left

💡 Hint

Common Mistakes

Using to_digit without an argument.

Trying to call a method that doesn't exist for char.

Using string methods instead of char methods.

To get the Unicode code point of a character like 'Z', cast it to u32 using as u32.

3fill in blank

hard

Fix the error in the code to check if a character is a digit.

Rust

let c = '5';
if c.[1]() {
    println!("It's a digit!");
}

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

Ais_alphanumeric

Bis_digit

Cis_numeric

Dis_alphabetic

Attempts:

3 left

💡 Hint

Common Mistakes

Using is_digit() without arguments (it requires a radix).

Using is_alphabetic() which checks for letters.

The correct method to check if a character is a digit is is_numeric() in Rust.

4fill in blank

hard

Fill both blanks to create a map from characters to their uppercase versions for letters only.

Rust

let letters = ['a', 'b', 'c', '1'];
let uppercase_map: std::collections::HashMap<char, char> = letters.iter()
    .filter(|&&c| c.[1]())
    .map(|&c| (c, c.[2]()))
    .collect();

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

Ais_alphabetic

Bto_ascii_uppercase

Cis_numeric

Dto_lowercase

Attempts:

3 left

💡 Hint

Common Mistakes

Filtering numeric characters instead of alphabetic.

Using to_lowercase() instead of uppercase.

Use is_alphabetic() to filter letters, and to_ascii_uppercase() to convert them to uppercase.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps characters to their Unicode code points if they are digits.

Rust

let chars = ['a', '3', '7', 'b'];
let digit_map: std::collections::HashMap<char, u32> = chars.iter()
    .filter(|&&c| c.[1]())
    .map(|&c| (c, c [2] [3]))
    .collect();

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

Ais_numeric

Bas

Cu32

Dis_alphabetic

Attempts:

3 left

💡 Hint

Common Mistakes

Using is_alphabetic() instead of is_numeric().

Forgetting to cast the character to u32.

Filter digits with is_numeric(), cast characters to u32 using as to get Unicode code points.

Practice

1. Which of the following correctly declares a char variable in Rust?

easy

A. let letter: char = `a`;

B. let letter: char = 'a';

C. let letter: char = a;

D. let letter: char = "a";

Solution

1. Step 1: Understand Rust char syntax

   Rust uses single quotes for char literals, e.g., 'a'. Double quotes are for strings.

2. Step 2: Check each option

   let letter: char = 'a'; uses single quotes correctly. let letter: char = "a"; uses double quotes (string). let letter: char = a; misses quotes. let letter: char = `a`; uses backticks, which is invalid.

3. Final Answer:

   let letter: char = 'a'; -> Option B

4. Quick Check:

   char uses single quotes [OK]

Hint: Remember: single quotes for char, double quotes for string [OK]

Common Mistakes:

• Using double quotes instead of single quotes
• Omitting quotes around the character
• Using backticks instead of quotes

2. Which of the following is the correct way to assign the emoji 😀 to a char variable in Rust?

easy

A. let smiley: char = '😀';

B. let smiley: char = 😀;

C. let smiley: char = "😀";

D. let smiley: char = `😀`;

Solution

1. Step 1: Recall char literal rules

   Rust char literals must be in single quotes, even for emojis.

2. Step 2: Evaluate options

   let smiley: char = '😀'; uses single quotes correctly with the emoji. Double quotes ("😀") create a string. Bare 😀 lacks quotes. Backticks (`😀`) are invalid.

3. Final Answer:

   let smiley: char = '😀'; -> Option A

4. Quick Check:

   Emoji char uses single quotes [OK]

Hint: Use single quotes for any char, including emojis [OK]

Common Mistakes:

• Using double quotes for char
• Not quoting the emoji
• Using backticks instead of single quotes

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

let c: char = 'Z';
println!("{}", c.is_alphabetic());

medium

A. true

B. false

C. Z

D. Compile error

Solution

1. Step 1: Understand is_alphabetic() method

   This method returns true if the char is a letter (A-Z or a-z or other alphabets).

2. Step 2: Check the character 'Z'

   'Z' is an uppercase letter, so is_alphabetic() returns true.

3. Final Answer:

   true -> Option A

4. Quick Check:

   'Z'.is_alphabetic() = true [OK]

Hint: Check if char is letter with is_alphabetic() method [OK]

Common Mistakes:

• Confusing output with printing the char itself
• Thinking is_alphabetic() returns the char
• Expecting a compile error

4. Identify the error in this Rust code snippet:

let ch: char = 'ab';

medium

A. Missing semicolon at the end

B. Use double quotes for multiple characters

C. char type cannot store letters

D. Multiple characters in single quotes are not allowed

Solution

1. Step 1: Check char literal rules

   A char can only hold one Unicode character, so 'ab' is invalid.

2. Step 2: Analyze the error

   Using multiple characters inside single quotes causes a compile error.

3. Final Answer:

   Multiple characters in single quotes are not allowed -> Option D

4. Quick Check:

   char holds one char only [OK]

Hint: char must be one character in single quotes [OK]

Common Mistakes:

• Trying to store multiple characters in a char
• Using double quotes for char
• Ignoring compile errors

5. Given a string slice let s = "Rust 🦀";, which Rust code correctly extracts the crab emoji as a char?

hard

A. let crab = s.chars().nth(4).unwrap();

B. let crab = s[5];

C. let crab = s.chars().nth(5).unwrap();

D. let crab = s[4..5].chars().next().unwrap();

Solution

1. Step 1: Understand string and char indexing in Rust

   Rust strings are UTF-8 encoded. The string "Rust 🦀" has 6 chars: 'R'(0),'u'(1),'s'(2),'t'(3),' '(4),'🦀'(5). Crab emoji is the 6th character (index 5), counting chars, not bytes.

2. Step 2: Check each option

   let crab = s.chars().nth(5).unwrap(); correctly uses chars().nth(5) to get the crab emoji. let crab = s.chars().nth(4).unwrap(); gets the space (index 4). let crab = s[5]; uses byte index (u8, not char). let crab = s[4..5].chars().next().unwrap(); byte slice yields space.

3. Final Answer:

   let crab = s.chars().nth(5).unwrap(); -> Option C

4. Quick Check:

   Use chars().nth(5) for crab emoji [OK]

Hint: Use chars().nth(index) to get char by position [OK]

Common Mistakes:

• Indexing string bytes directly
• Using wrong index for emoji
• Not unwrapping Option from nth()