If expression in Rust - Mini Project: Build & Apply

Using If Expression in Rust

📖 Scenario: Imagine you are building a simple program that decides if a person is old enough to vote. Voting age is 18 years or older.

🎯 Goal: You will create a program that uses an if expression to check a person's age and print whether they can vote or not.

📋 What You'll Learn

Create a variable called age with the value 20

Create a variable called voting_eligibility that uses an if expression to check if age is 18 or more

Use if expression to assign "Can vote" if age is 18 or more, otherwise "Cannot vote"

Print the value of voting_eligibility

💡 Why This Matters

🌍 Real World

Checking conditions like age eligibility is common in many programs, such as voting systems, age-restricted content, or membership access.

💼 Career

Understanding if expressions is fundamental for decision-making in programming, useful in almost every software development job.

1

Create the age variable

Create a variable called age and set it to 20.

Rust

# Create a variable called age and set it to 20
# Your code here

Hint

Use let to create a variable and assign the number 20 to age.

2

Create the voting eligibility variable using if expression

Create a variable called voting_eligibility that uses an if expression to check if age is 18 or more. Assign "Can vote" if true, otherwise "Cannot vote".

Rust

let age = 20;
# Create voting_eligibility using if expression to check age
# Your code here

Hint

Use if age >= 18 { "Can vote" } else { "Cannot vote" } to assign the value.

3

Print the voting eligibility

Write a println! statement to print the value of voting_eligibility.

Rust

let age = 20;
let voting_eligibility = if age >= 18 { "Can vote" } else { "Cannot vote" };
# Print voting_eligibility
# Your code here

Hint

Use println!("{}", voting_eligibility); to show the result.

4

Run and see the result

Run the program and observe the output. It should print Can vote.

Rust

let age = 20;
let voting_eligibility = if age >= 18 { "Can vote" } else { "Cannot vote" };
println!("{}", voting_eligibility);
# Run the program to see the output

Hint

The program should print Can vote because age is 20 which is 18 or more.

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