Integer types in Rust - Mini Project: Build & Apply

Integer types

📖 Scenario: You are working on a simple program that stores and displays different integer values representing ages and counts in a small shop.

🎯 Goal: Learn how to create variables with different integer types in Rust and print their values.

📋 What You'll Learn

Create variables with specific integer types

Assign exact integer values to these variables

Print the values to the console

💡 Why This Matters

🌍 Real World

Integer types are used in programs to store numbers like ages, counts, and totals with different size limits and signs.

💼 Career

Understanding integer types and casting is important for writing safe and efficient code in systems programming and many software development jobs.

1

Create integer variables

Create a variable called age of type u8 and set it to 30. Also create a variable called count of type i16 and set it to -15.

Rust

// Create a variable called age of type u8 and set it to 30
// Create a variable called count of type i16 and set it to -15

Hint

Use let keyword to create variables with explicit types like u8 and i16.

2

Add another integer variable

Add a variable called total of type i32 and set it to 1000.

Rust

fn main() {
    let age: u8 = 30;
    let count: i16 = -15;
    // Add a variable called total of type i32 and set it to 1000
}

Hint

Use let total: i32 = 1000; to create the variable.

3

Use variables in a calculation

Create a variable called net of type i32 that adds total and count.

Rust

fn main() {
    let age: u8 = 30;
    let count: i16 = -15;
    let total: i32 = 1000;
    // Create a variable net of type i32 that adds total and count
}

Hint

Cast count to i32 before adding to total.

4

Print the values

Print the values of age, count, total, and net using println! with labels.

Rust

fn main() {
    let age: u8 = 30;
    let count: i16 = -15;
    let total: i32 = 1000;
    let net: i32 = total + count as i32;
    // Print age, count, total, and net with labels
}

Hint

Use println!("Label: {}", variable); to print each variable with a label.

Practice

1. Which Rust integer type can store only positive whole numbers including zero?

easy

A. u32

B. i32

C. f32

D. bool

Solution

1. Step 1: Understand signed vs unsigned integers

   Signed integers (i32) store negative and positive numbers, unsigned (u32) store only zero and positive numbers.

2. Step 2: Identify the type that stores only positive whole numbers

   u32 is unsigned 32-bit integer, so it stores only positive whole numbers including zero.

3. Final Answer:

   u32 -> Option A

4. Quick Check:

   Unsigned integer = u32 [OK]

Hint: Unsigned integers start with 'u' and hold only positive numbers [OK]

Common Mistakes:

• Confusing signed and unsigned types
• Choosing floating-point types for whole numbers
• Thinking bool is an integer type

2. Which of the following is the correct way to declare a 16-bit signed integer variable named x with value 100 in Rust?

easy

A. let x: u16 = 100;

B. let x: i16 = 100;

C. let x i16 = 100;

D. let x: int16 = 100;

Solution

1. Step 1: Check Rust syntax for typed variable declaration

   Rust uses let variable_name: type = value; syntax.

2. Step 2: Identify the correct 16-bit signed integer type

   i16 is the 16-bit signed integer type in Rust.

3. Final Answer:

   let x: i16 = 100; -> Option B

4. Quick Check:

   Typed variable declaration with i16 = let x: i16 = 100; [OK]

Hint: Use 'let var: i16 = value;' for 16-bit signed integers [OK]

Common Mistakes:

• Using unsigned type u16 instead of signed
• Using invalid type name int16
• Incorrect syntax like missing colon

3. What will be the output of this Rust code?

let a: i8 = 127;
let b: i8 = 1;
let c = a.wrapping_add(b);
println!("{}", c);

medium

A. 128

B. 0

C. -128

D. Overflow error

Solution

1. Step 1: Understand i8 max value and wrapping_add behavior

   The max value for i8 is 127. Adding 1 causes overflow. wrapping_add wraps around instead of panicking.

2. Step 2: Calculate the wrapped result

   127 + 1 wraps to -128 in i8 range.

3. Final Answer:

   -128 -> Option C

4. Quick Check:

   Wrapping addition overflow wraps to -128 [OK]

Hint: wrapping_add wraps on overflow, not error [OK]

Common Mistakes:

• Expecting 128 which is out of i8 range
• Thinking it causes runtime panic
• Confusing wrapping_add with normal addition

4. Identify the error in this Rust code snippet:

let x: u8 = -5;

medium

A. Missing semicolon

B. Type u8 does not exist

C. Variable name invalid

D. Negative value assigned to unsigned integer

Solution

1. Step 1: Check the type and value compatibility

   u8 is unsigned 8-bit integer and cannot hold negative values.

2. Step 2: Identify the error cause

   Assigning -5 to u8 causes a type mismatch error.

3. Final Answer:

   Negative value assigned to unsigned integer -> Option D

4. Quick Check:

   Unsigned integer cannot hold negative values [OK]

Hint: Unsigned types cannot hold negative numbers [OK]

Common Mistakes:

• Ignoring negative sign allowed in unsigned types
• Thinking semicolon is missing
• Assuming variable name is invalid

5. You need to store the number of stars in the Milky Way galaxy, approximately 20,000,000,000,000,000,000 (20 quintillion). Which Rust integer type should you choose to store this number safely?

hard

A. u128

B. i64

C. u64

D. i32

Solution

1. Step 1: Understand the size limits of integer types

   u64 max is about 18 quintillion, which cannot hold 20 quintillion. i64 max is about 9 quintillion. u128 is necessary.

2. Step 2: Choose the type that safely stores 20 quintillion

   u128 can store very large positive integers up to 3.4e38, safely holding 20 quintillion.

3. Final Answer:

   u128 -> Option A

4. Quick Check:

   Use u128 for very large positive integers [OK]

Hint: Use u128 for very large positive integers beyond u64 [OK]

Common Mistakes:

• Choosing signed types unnecessarily
• Using i32 which is too small
• Assuming u64 is always enough without checking limits