Scalar data types in Rust - Mini Project: Build & Apply

Understanding Scalar Data Types in Rust

📖 Scenario: You are learning Rust programming and want to understand how to use scalar data types. Scalars are the simplest types that hold a single value, like numbers and characters.

🎯 Goal: Build a small Rust program that declares variables of different scalar types and prints their values.

📋 What You'll Learn

Declare variables with scalar types: i32, f64, char, and bool

Assign exact values to these variables

Print the values of these variables

💡 Why This Matters

🌍 Real World

Scalar data types are the building blocks for storing simple values like counts, measurements, letters, and true/false flags in any Rust program.

💼 Career

Understanding scalar types is essential for writing safe and efficient Rust code, which is valuable in systems programming, embedded development, and performance-critical applications.

1

Declare an integer variable

Create a variable called my_integer of type i32 and assign it the value 42.

Rust

# Your code here

Hint

Use let to declare a variable and specify the type with a colon.

2

Add a floating-point variable

Add a variable called my_float of type f64 and assign it the value 3.14 below the integer variable.

Rust

fn main() {
    let my_integer: i32 = 42;
    # Your code here
}

Hint

Remember to use let and specify the type f64 for floating-point numbers.

3

Add a character and a boolean variable

Add two variables: my_char of type char with value 'R', and my_bool of type bool with value true below the previous variables.

Rust

fn main() {
    let my_integer: i32 = 42;
    let my_float: f64 = 3.14;
    # Your code here
}

Hint

Use single quotes for char values and true or false for bool.

4

Print all variables

Use println! to print the values of my_integer, my_float, my_char, and my_bool each on its own line.

Rust

fn main() {
    let my_integer: i32 = 42;
    let my_float: f64 = 3.14;
    let my_char: char = 'R';
    let my_bool: bool = true;
    # Your code here
}

Hint

Use println!("{}", variable); to print each variable on its own line.

Practice

1. Which of the following is NOT a scalar data type in Rust?

easy

A. Integer

B. Boolean

C. Array

D. Character

Solution

1. Step 1: Recall scalar data types in Rust

   Scalar types include integers, floats, booleans, and characters, which hold a single value.

2. Step 2: Identify the non-scalar type

   An array holds multiple values and is a compound type, not scalar.

3. Final Answer:

   Array -> Option C

4. Quick Check:

   Scalar types exclude arrays [OK]

Hint: Scalar types hold one value; arrays hold many [OK]

Common Mistakes:

• Confusing arrays with scalar types
• Thinking floats are not scalar
• Mixing compound and scalar types

2. Which of the following is the correct way to declare a boolean variable named is_active set to true in Rust?

easy

A. let is_active: bool = true;

B. let is_active = True;

C. let is_active = 1;

D. let is_active: boolean = true;

Solution

1. Step 1: Check Rust boolean syntax

   Rust uses lowercase true and false for booleans, and the type is bool.

2. Step 2: Validate each option

   let is_active: bool = true; correctly declares is_active as a bool with value true. let is_active = True; uses uppercase True which is invalid. let is_active = 1; assigns an integer, not a boolean. let is_active: boolean = true; uses boolean which is not a Rust type.

3. Final Answer:

   let is_active: bool = true; -> Option A

4. Quick Check:

   Boolean type is bool and value is lowercase true [OK]

Hint: Booleans use lowercase true/false and type bool [OK]

Common Mistakes:

• Using uppercase True/False
• Using wrong type name boolean
• Assigning integers to booleans

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

let x: i32 = 10;
let y: f64 = 3.5;
println!("{}", x as f64 + y);

medium

A. 13

B. 13.5

C. Type error

D. 10.0

Solution

1. Step 1: Understand type casting in the code

   The integer x is cast to f64 using as f64, so 10 becomes 10.0.

2. Step 2: Perform the addition

   Adding 10.0 (casted x) and 3.5 (y) results in 13.5.

3. Final Answer:

   13.5 -> Option B

4. Quick Check:

   Cast integer to float, then add floats = 13.5 [OK]

Hint: Cast integers to float before adding floats [OK]

Common Mistakes:

• Forgetting to cast integer
• Expecting integer addition
• Assuming type error without cast

4. Identify the error in the following Rust code snippet:

let letter: char = "a";

medium

A. Missing semicolon

B. char cannot be assigned a letter

C. Variable name is invalid

D. char type must use single quotes, not double quotes

Solution

1. Step 1: Check char literal syntax

   In Rust, char literals must be enclosed in single quotes, e.g., 'a', not double quotes.

2. Step 2: Analyze the code

   The code uses double quotes "a", which is a string slice, not a char. This causes a type mismatch error.

3. Final Answer:

   char type must use single quotes, not double quotes -> Option D

4. Quick Check:

   char literals use single quotes 'a' [OK]

Hint: Use single quotes for char, double quotes for strings [OK]

Common Mistakes:

• Using double quotes for char
• Confusing char with string
• Ignoring type mismatch errors

5. You want to store the temperature reading 36.6 in Rust using scalar types. Which declaration is best and why?

Options:
A) let temp: i32 = 36.6;
B) let temp: char = '36';
C) let temp: bool = true;
D) let temp: f64 = 36.6;

hard

A. let temp: f64 = 36.6; because floats store decimal numbers

B. let temp: char = '36'; because characters store numbers

C. let temp: bool = true; because temperature is true or false

D. let temp: i32 = 36.6; because integers store decimal numbers

Solution

1. Step 1: Understand the data type needed for decimal numbers

   Temperature 36.6 has a decimal part, so it requires a floating-point type like f64.

2. Step 2: Evaluate each option

   let temp: i32 = 36.6; because integers store decimal numbers tries to assign a decimal to an integer, which is invalid. let temp: f64 = 36.6; because floats store decimal numbers correctly uses f64 for decimals. let temp: bool = true; because temperature is true or false uses boolean, which is unrelated. let temp: char = '36'; because characters store numbers uses char with invalid multi-character literal.

3. Final Answer:

   let temp: f64 = 36.6; because floats store decimal numbers -> Option A

4. Quick Check:

   Decimal numbers need float types like f64 [OK]

Hint: Use float types for decimal numbers like temperature [OK]

Common Mistakes:

• Assigning decimals to integers
• Using bool for numeric values
• Using char for multi-digit numbers