If expression in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print "Positive" if the number is greater than zero.

Rust

let number = 5;
if number [1] 0 {
    println!("Positive");
}

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

A<

B!=

C==

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' will check for negative numbers.

Using '==' checks for equality, not greater than.

The condition number > 0 checks if the number is positive.

2fill in blank

medium

Complete the code to assign the string "even" or "odd" based on the number.

Rust

let number = 4;
let result = if number % 2 [1] 0 { "even" } else { "odd" };

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

A==

B!=

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' will assign 'even' to odd numbers.

Using '>' or '<' does not correctly check for evenness.

The expression number % 2 == 0 checks if the number is even.

3fill in blank

hard

Fix the error in the if expression to correctly assign the maximum of two numbers.

Rust

let a = 10;
let b = 20;
let max = if a [1] b { b } else { a };

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

A<

B>

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' will assign a as max incorrectly.

Using '==' or '!=' does not find the maximum.

The condition a < b means if a is less than b, then b is the max.

4fill in blank

hard

Fill in the blank to create a dictionary with word lengths for words longer than 3 letters.

Rust

let words = ["cat", "house", "dog", "elephant"];
let lengths = words.iter()
    .filter(|&word| word.len() [1] 3)
    .map(|word| (word, word.len()))
    .collect::<std::collections::HashMap<_, _>>();

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

A!=

B>

C==

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' will select shorter words.

Using '==' will select only words of length 3.

The word.len() > 3 filters words longer than 3 letters.

5fill in blank

hard

Fill the blanks to create a HashMap of uppercase words and their lengths for words longer than 4 letters.

Rust

let words = ["apple", "bat", "carrot", "dog"];
let result = words.iter()
    .filter(|&word| word.len() [1] 4)
    .map(|word| (word.[2](), word.len()))
    .collect::<std::collections::HashMap<_, _>>();

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

A<

B>

Cto_uppercase

Dto_lowercase

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' will select shorter words.

Using 'to_lowercase' will convert words to lowercase instead of uppercase.

The filter selects words longer than 4 letters, then maps each word to its uppercase form and length.

Practice

1. What does an if expression do in Rust?

easy

A. It chooses between code blocks based on a condition.

B. It repeats code multiple times.

C. It defines a new function.

D. It declares a variable.

Solution

1. Step 1: Understand the purpose of if

   The if expression checks a condition to decide which code block to run.

2. Step 2: Compare with other options

   Repeating code is done by loops, functions define behavior, and variables store data, so these are incorrect.

3. Final Answer:

   It chooses between code blocks based on a condition. -> Option A

4. Quick Check:

   If expression = choose code [OK]

Hint: If checks true/false to pick code [OK]

Common Mistakes:

• Confusing if with loops
• Thinking if declares variables
• Mixing if with function definitions

2. Which of the following is the correct syntax for an if expression in Rust?

easy

A. if condition: { /* code */ } else: { /* code */ }

B. if condition { /* code */ } else { /* code */ }

C. if (condition) then { /* code */ } else { /* code */ }

D. if condition -> { /* code */ } else -> { /* code */ }

Solution

1. Step 1: Recall Rust if syntax

   Rust uses if condition { ... } else { ... } without parentheses or arrows.

2. Step 2: Check each option

   if condition { /* code */ } else { /* code */ } matches Rust syntax; others use invalid keywords or symbols.

3. Final Answer:

   if condition { /* code */ } else { /* code */ } -> Option B

4. Quick Check:

   Rust if syntax = braces, no parentheses [OK]

Hint: Rust if uses braces, no parentheses [OK]

Common Mistakes:

• Adding parentheses like other languages
• Using 'then' keyword
• Using colons or arrows incorrectly

3. What is the output of this Rust code?

let x = 10;
let y = if x > 5 { "big" } else { "small" };
println!("{}", y);

medium

A. Compilation error

B. small

C. big

D. 10

Solution

1. Step 1: Evaluate the condition x > 5

   Since x is 10, which is greater than 5, the condition is true.

2. Step 2: Determine which branch runs

   The if expression returns "big" because the condition is true, so y is assigned "big".

3. Final Answer:

   big -> Option C

4. Quick Check:

   10 > 5 is true, so output = big [OK]

Hint: Check condition true or false to pick output [OK]

Common Mistakes:

• Confusing output with variable x
• Thinking else branch runs
• Expecting numeric output

4. Identify the error in this Rust code snippet:

let number = 7;
let result = if number % 2 == 0 {
    "even"
} else {
    "odd"
};
println!("{}", result);

medium

A. No error, code runs correctly

B. Mismatched types in if and else branches

C. Missing semicolon after if expression

D. Using % operator incorrectly

Solution

1. Step 1: Check syntax and types

   The if expression returns string slices "even" or "odd", both same type, so no type mismatch.

2. Step 2: Verify semicolons and operators

   The semicolon after the if expression is present, and the modulo operator is used correctly.

3. Final Answer:

   No error, code runs correctly -> Option A

4. Quick Check:

   Correct syntax and types = no error [OK]

Hint: Check types and semicolons carefully [OK]

Common Mistakes:

• Thinking semicolon is missing
• Confusing types in branches
• Misusing modulo operator

5. How can you use an if expression to assign a value to a variable based on multiple conditions in Rust? Choose the correct code snippet.

hard

A. let grade = if score >= 90 -> 'A' else if score >= 80 -> 'B' else -> 'C';

B. let grade = if (score >= 90) then 'A' else if (score >= 80) then 'B' else 'C';

C. let grade = if score >= 90: 'A' elif score >= 80: 'B' else: 'C';

D. let grade = if score >= 90 { 'A' } else if score >= 80 { 'B' } else { 'C' };

Solution

1. Step 1: Understand Rust's if-else if syntax

   Rust uses if condition { value } and else if condition { value } blocks with braces, no keywords like then or arrows.

2. Step 2: Check each option for syntax correctness

   let grade = if score >= 90 { 'A' } else if score >= 80 { 'B' } else { 'C' }; uses correct Rust syntax; others use invalid keywords or punctuation.

3. Final Answer:

   let grade = if score >= 90 { 'A' } else if score >= 80 { 'B' } else { 'C' }; -> Option D

4. Quick Check:

   Rust if-else if uses braces, no then [OK]

Hint: Use braces and else if without extra keywords [OK]

Common Mistakes:

• Adding 'then' keyword
• Using colons or arrows
• Incorrect else if syntax