Arithmetic operators in Rust - Mini Project: Build & Apply

Arithmetic Operators in Rust

📖 Scenario: You are helping a small shop calculate prices for items bought by customers. You will use arithmetic operators to add, subtract, multiply, and divide numbers.

🎯 Goal: Build a Rust program that uses arithmetic operators to calculate the total price, discount, and final price for a product.

📋 What You'll Learn

Create variables with exact values for price and quantity

Create a variable for discount rate

Calculate total price and discount amount using arithmetic operators

Print the final price after discount

💡 Why This Matters

🌍 Real World

Calculating prices, discounts, and totals is common in shopping apps and billing systems.

💼 Career

Understanding arithmetic operations and data types is essential for software development, especially in finance and retail applications.

1

Create initial variables for price and quantity

Create a variable called price with the value 50.0 and a variable called quantity with the value 3.

Rust

# Create variables price and quantity with given values
// Your code here

Hint

Use let to create variables. Price is a floating-point number, quantity is an integer.

2

Add a discount rate variable

Add a variable called discount_rate with the value 0.1 to represent a 10% discount.

Rust

fn main() {
    let price = 50.0;
    let quantity = 3;
    // Add discount_rate variable here
    // Your code here
}

Hint

Discount rate is a floating-point number between 0 and 1.

3

Calculate total price and discount amount

Create a variable called total_price that multiplies price and quantity. Then create a variable called discount_amount that multiplies total_price and discount_rate.

Rust

fn main() {
    let price = 50.0;
    let quantity = 3;
    let discount_rate = 0.1;
    // Calculate total_price and discount_amount
    // Your code here
}

Hint

Multiply price and quantity. Convert quantity to f64 to match price type.

4

Print the final price after discount

Calculate the final price by subtracting discount_amount from total_price and print it using println! with the message: "Final price: {final_price}".

Rust

fn main() {
    let price = 50.0;
    let quantity = 3;
    let discount_rate = 0.1;
    let total_price = price * quantity as f64;
    let discount_amount = total_price * discount_rate;
    // Calculate final_price and print it
    // Your code here
}

Hint

Subtract discount_amount from total_price. Use println!("Final price: {}", final_price); to show the result.

Practice

1. Which arithmetic operator in Rust is used to find the remainder of a division?

easy

A. The - operator

B. The / operator

C. The * operator

D. The % operator

Solution

1. Step 1: Understand the meaning of each operator

   The / operator divides, * multiplies, - subtracts, and % gives the remainder after division.

2. Step 2: Identify the operator for remainder

   The % operator returns the remainder when one number is divided by another.

3. Final Answer:

   The % operator -> Option D

4. Quick Check:

   Remainder operator = % [OK]

Hint: Remainder always uses % in math [OK]

Common Mistakes:

• Confusing / with %, thinking / gives remainder
• Using * or - for remainder
• Mixing up operator symbols

2. Which of the following is the correct way to write multiplication of two variables a and b in Rust?

easy

A. a * b

B. a x b

C. a . b

D. a & b

Solution

1. Step 1: Recall Rust arithmetic syntax

   Rust uses * for multiplication, not x, ., or &.

2. Step 2: Confirm correct operator

   The expression a * b correctly multiplies a and b.

3. Final Answer:

   a * b -> Option A

4. Quick Check:

   Multiplication operator = * [OK]

Hint: Use * for multiplication in Rust [OK]

Common Mistakes:

• Using x instead of *
• Using . or & which are not arithmetic
• Confusing syntax with other languages

3. What is the output of the following Rust code?

let x = 10;
let y = 3;
let result = x / y;
println!("{}", result);

medium

A. 4

B. 3.3333

C. 3

D. Syntax error

Solution

1. Step 1: Understand integer division in Rust

   Both x and y are integers, so x / y performs integer division, dropping decimals.

2. Step 2: Calculate integer division

   10 divided by 3 is 3.3333, but integer division truncates to 3.

3. Final Answer:

   3 -> Option C

4. Quick Check:

   Integer division truncates decimals = 3 [OK]

Hint: Integer division drops decimals, use floats for precise result [OK]

Common Mistakes:

• Expecting decimal result with integer division
• Confusing integer and float division
• Assuming syntax error due to println!

4. Identify the error in this Rust code snippet:

let a = 5;
let b = 2;
let c = a / b.0;
println!("{}", c);

medium

A. Variables a and b are not declared

B. Using .0 on integer causes error

C. Missing semicolon after println!

D. Division operator / is invalid

Solution

1. Step 1: Analyze the expression a / b.0

   The code tries to access .0 on b, which is an integer, not a tuple or struct.

2. Step 2: Understand why .0 causes error

   Only tuples or structs have fields like .0; integers do not, so this causes a compile error.

3. Final Answer:

   Using .0 on integer causes error -> Option B

4. Quick Check:

   Integer has no .0 field = error [OK]

Hint: Only tuples/structs have .0, not integers [OK]

Common Mistakes:

• Thinking / is invalid operator
• Missing semicolon causes error
• Assuming variables are undeclared

5. You want to calculate the average of two integers a and b in Rust and get a float result. Which code snippet correctly does this?

hard

A. let avg = (a + b) as f64 / 2.0;

B. let avg = (a + b) / 2.0;

C. let avg = (a + b) / 2;

D. let avg = (a + b) / 2 as f64;

Solution

1. Step 1: Understand type conversion for float division

   To get a float result, convert integers to float before division.

2. Step 2: Check each option for correct syntax and types

   let avg = (a + b) / 2; does integer division, no float result. let avg = (a + b) as f64 / 2.0; converts sum to f64, divides by 2.0 (float), correct. let avg = (a + b) / 2.0; divides integer sum by float 2.0 without conversion, invalid. let avg = (a + b) / 2 as f64; tries to cast 2 to f64 before division (due to `as` precedence), invalid.

3. Final Answer:

   let avg = (a + b) as f64 / 2.0; -> Option A

4. Quick Check:

   Convert to float before dividing by float [OK]

Hint: Cast sum to float before dividing by float [OK]

Common Mistakes:

• Dividing integers by float without cast
• Casting after division
• Using integer division expecting float result