If–else expression in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to assign 10 to x if condition is true, otherwise 5.

Rust

let x = if condition [1] 10 else 5;

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

A==

B{

C;

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using a semicolon instead of braces after if condition.

Trying to use == instead of braces for the if block.

The if–else expression in Rust uses braces {} to enclose the blocks of code for each condition.

2fill in blank

medium

Complete the code to assign the larger of a and b to max using if–else expression.

Rust

let max = if a > b [1] a else b;

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

A;

B:

Cthen

D{

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'then' keyword which Rust does not have.

Omitting braces around the values.

In Rust, the if and else blocks must be enclosed in braces to form an expression.

3fill in blank

hard

Fix the error in the if–else expression to correctly assign a value to result.

Rust

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

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

A{

B;

C:

Dthen

Attempts:

3 left

💡 Hint

Common Mistakes

Using semicolon instead of braces.

Using 'then' keyword which Rust does not support.

Rust requires braces around the blocks in if–else expressions, even for single expressions.

4fill in blank

hard

Complete the code to create a conditional expression that assigns 'positive' or 'non-positive' to status.

Rust

let status = if number {BLANK_1}} 0 { "positive" else "non-positive";

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

A>

B{

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using less than or equal operator in the condition.

Omitting braces after the if condition.

The condition uses > to check if number is greater than zero, and braces to group the true block.

5fill in blank

hard

Fill all three blanks to assign a grade based on score using nested if–else expressions.

Rust

let grade = if score >= 90 [1] "A" else if score >= 80 [2] "B" else [3] "C";

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

A{

D;

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting braces around nested if blocks.

Using semicolons instead of braces.

Each if and else if block must be enclosed in braces to form valid Rust expressions.

Practice

1. What does an if-else expression in Rust do?

easy

A. Declares a variable without value

B. Repeats a block of code multiple times

C. Defines a new function

D. Chooses between two options and returns a value

Solution

1. Step 1: Understand the purpose of if-else

   An if-else expression lets the program pick one of two paths based on a condition.

2. Step 2: Recognize that it returns a value

   In Rust, if-else expressions return a value that can be stored in a variable.

3. Final Answer:

   Chooses between two options and returns a value -> Option D

4. Quick Check:

   If-else expression = choice with value [OK]

Hint: If-else picks one path and returns a value [OK]

Common Mistakes:

• Thinking if-else repeats code like a loop
• Confusing if-else with function definition
• Ignoring that if-else returns a value

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

easy

A. let x = if condition { 5 } else { 10 };

B. if (condition) then { 5 } else { 10 };

C. let x = if condition: 5 else: 10;

D. let x = if condition { 5 } elseif { 10 };

Solution

1. Step 1: Check Rust if-else syntax

   Rust uses if condition { value1 } else { value2 } with braces and no parentheses.

2. Step 2: Identify correct option

   let x = if condition { 5 } else { 10 }; matches Rust syntax exactly with variable assignment and braces.

3. Final Answer:

   let x = if condition { 5 } else { 10 }; -> Option A

4. Quick Check:

   Rust if-else syntax = let x = if condition { 5 } else { 10 }; [OK]

Hint: Use braces and no parentheses in Rust if-else [OK]

Common Mistakes:

• Using parentheses around condition
• Writing elseif instead of else if
• Using colons instead of braces

3. What is the output of this Rust code?

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

medium

A. odd

B. even

C. 7

D. Syntax error

Solution

1. Step 1: Check the condition number % 2 == 0

   7 % 2 equals 1, which is not 0, so condition is false.

2. Step 2: Determine which branch runs

   Since condition is false, the else branch runs, returning "odd".

3. Final Answer:

   odd -> Option A

4. Quick Check:

   7 is odd, so output = odd [OK]

Hint: Check condition result to pick if or else branch [OK]

Common Mistakes:

• Assuming 7 is even
• Confusing modulo operator
• Expecting number to print instead of result

4. Identify the error in this Rust code:

let x = 10;
let y = if x > 5 { 1 };
println!("{}", y);

medium

A. Variable y is not declared

B. Incorrect comparison operator

C. Missing else branch in if expression

D. println! macro syntax error

Solution

1. Step 1: Check if-else expression completeness

   When assigning with if, Rust requires both if and else branches to return a value.

2. Step 2: Identify missing else branch

   The code has no else branch, so y's value is undefined, causing a compile error.

3. Final Answer:

   Missing else branch in if expression -> Option C

4. Quick Check:

   if-else must have else when used as expression [OK]

Hint: Always include else when assigning from if [OK]

Common Mistakes:

• Forgetting else branch when assigning
• Thinking if alone returns a value
• Misreading error as println! issue

5. You want to assign a variable grade based on a score: if score is 90 or above, grade is 'A', else 'F'. Which code correctly uses if-else expression?

hard

A. let grade = if score > 90 { 'A' } else if score < 90 { 'F' };

B. let grade = if score >= 90 { 'A' } else { 'F' };

C. let grade = if score >= 90 { 'A' }; else { 'F' };

D. let grade = if score >= 90 then { 'A' } else { 'F' };

Solution

1. Step 1: Check correct if-else expression syntax

   Rust uses if condition { value } else { value } without 'then' or semicolons inside.

2. Step 2: Validate condition and branches

   let grade = if score >= 90 { 'A' } else { 'F' }; correctly checks >= 90 and returns 'A' or 'F' in else branch.

3. Final Answer:

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

4. Quick Check:

   Correct syntax and logic = let grade = if score >= 90 { 'A' } else { 'F' }; [OK]

Hint: Use braces and else for complete if-else expression [OK]

Common Mistakes:

• Using 'then' keyword
• Missing else branch
• Incorrect semicolon placement