Using if as expression in Rust - Mini Project: Build & Apply

Using if as expression

📖 Scenario: You are building a simple program to decide if a person is an adult or a minor based on their age.

🎯 Goal: Create a Rust program that uses if as an expression to assign a message depending on the age.

📋 What You'll Learn

Create a variable age with the value 20

Create a variable status that uses if as an expression to assign "Adult" if age is 18 or more, otherwise "Minor"

Print the status variable

💡 Why This Matters

🌍 Real World

Using <code>if</code> as an expression helps write concise code for decisions like checking age limits.

💼 Career

Understanding expressions and conditional assignments is important for writing clean and efficient Rust code in real projects.

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 age = 20; to create the variable.

2

Create the status variable using if as expression

Create a variable called status that uses if as an expression to assign "Adult" if age is 18 or more, otherwise assign "Minor".

Rust

fn main() {
    let age = 20;
    // Create status using if as expression
    // Your code here
}

Hint

Use let status = if age >= 18 { "Adult" } else { "Minor" };.

3

Print the status variable

Add a println! statement to print the status variable.

Rust

fn main() {
    let age = 20;
    let status = if age >= 18 { "Adult" } else { "Minor" };
    // Print the status variable
    // Your code here
}

Hint

Use println!("{}", status); to print the message.

4

Run the program to see the output

Run the program and observe the output. It should print Adult.

Rust

fn main() {
    let age = 20;
    let status = if age >= 18 { "Adult" } else { "Minor" };
    println!("{}", status);
}

// Run the program to see the output

Hint

The program prints Adult because age is 20.

Practice

1. What does using if as an expression in Rust allow you to do?

easy

A. Define functions inside an if statement

B. Only execute code blocks without returning values

C. Assign a value based on a condition directly to a variable

D. Create loops that run while a condition is true

Solution

1. Step 1: Understand the role of if as expression

   In Rust, if can return a value, unlike some languages where it only controls flow.

2. Step 2: Recognize assignment usage

   This means you can assign a variable directly using let x = if condition { value1 } else { value2 };.

3. Final Answer:

   Assign a value based on a condition directly to a variable -> Option C

4. Quick Check:

   if as expression = assign value [OK]

Hint: Think of if as a value picker, not just a decision maker [OK]

Common Mistakes:

• Thinking if can't return values
• Confusing if expression with loops
• Assuming if can define functions

2. Which of the following is the correct syntax for using if as an expression to assign a value in Rust?

easy

A. let x = if (condition) then 10 else 20;

B. let x = if condition { 10 } else { 20 };

C. let x = if condition: 10 else: 20;

D. let x = if condition { 10 } else 20;

Solution

1. Step 1: Recall Rust if expression syntax

   Rust uses curly braces for blocks and requires both if and else blocks to be enclosed in braces when returning values.

2. Step 2: Check each option

   let x = if condition { 10 } else { 20 }; correctly uses if condition { 10 } else { 20 };. Others use invalid syntax like missing braces or keywords.

3. Final Answer:

   let x = if condition { 10 } else { 20 }; -> Option B

4. Quick Check:

   Correct Rust if expression syntax = let x = if condition { 10 } else { 20 }; [OK]

Hint: Remember: Rust uses braces {} for both if and else blocks [OK]

Common Mistakes:

• Omitting braces around else block
• Using 'then' keyword (not in Rust)
• 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. even

B. 7

C. Compilation error

D. odd

Solution

1. Step 1: Evaluate the condition

   The condition checks if 7 modulo 2 equals 0. Since 7 % 2 is 1, the condition is false.

2. Step 2: Determine which branch runs

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

3. Final Answer:

   odd -> Option D

4. Quick Check:

   7 is odd = odd [OK]

Hint: Check the condition result carefully before picking output [OK]

Common Mistakes:

• Assuming 7 % 2 == 0 is true
• Confusing output with the number itself
• Expecting a syntax error

4. Identify the error in this Rust code using if as expression:

let x = if true { 5 } else { "five" };

medium

A. Mismatched types in if and else branches

B. Missing semicolon after else block

C. Cannot use if as expression in let binding

D. Condition must be a variable, not a literal

Solution

1. Step 1: Check types returned by if and else

   The if branch returns an integer 5, the else branch returns a string "five".

2. Step 2: Understand Rust type rules for if expressions

   Both branches must return the same type because the if expression must have a single consistent type.

3. Final Answer:

   Mismatched types in if and else branches -> Option A

4. Quick Check:

   if branches must match types = Mismatched types in if and else branches [OK]

Hint: Ensure both if and else return same type [OK]

Common Mistakes:

• Ignoring type mismatch errors
• Thinking semicolon is missing
• Believing literals can't be conditions

5. You want to assign a variable status based on a score: if score >= 90, status is "Excellent"; if score >= 60, status is "Pass"; otherwise, "Fail". Which Rust code correctly uses nested if expressions to do this?

hard

A. let status = if score >= 90 { "Excellent" } else if score >= 60 { "Pass" } else { "Fail" };

B. let status = if score >= 90 { "Excellent" } else { if score >= 60 { "Pass" } else "Fail" };

C. let status = if score >= 90 { "Excellent" } else if score >= 60 { "Pass" }; else { "Fail" };

D. let status = if score >= 90 { "Excellent" } else { "Pass" } else { "Fail" };

Solution

1. Step 1: Understand nested if expressions

   Rust supports chaining if and else if expressions to select among multiple conditions.

2. Step 2: Check syntax correctness

   let status = if score >= 90 { "Excellent" } else if score >= 60 { "Pass" } else { "Fail" }; correctly uses else if and ends with else block. let status = if score >= 90 { "Excellent" } else { if score >= 60 { "Pass" } else { "Fail" } }; nests if inside else but is more verbose. Options C and D have syntax errors.

3. Final Answer:

   let status = if score >= 90 { "Excellent" } else if score >= 60 { "Pass" } else { "Fail" }; -> Option A

4. Quick Check:

   Use else if for clean multi-condition if expressions [OK]

Hint: Use else if for multiple conditions, not nested if inside else [OK]

Common Mistakes:

• Missing else block causing syntax error
• Incorrect semicolon placement
• Using multiple else blocks