Scalar data types in Rust - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Rust code with scalar types?

Consider the following Rust code snippet. What will it print when run?

Rust

fn main() {
    let x: i32 = 10;
    let y: f64 = 3.5;
    let z: bool = (x as f64) > y;
    println!("{}", z);
}

A false

B true

C 3.5

D Compilation error

💡 Hint

Remember that casting i32 to f64 allows comparison between x and y.

The integer 10 is cast to 10.0 as f64, which is greater than 3.5, so z is true.

❓ Predict Output

intermediate

What value does this Rust code assign to variable `c`?

Given the code below, what is the value of `c` after execution?

Rust

fn main() {
    let a: u8 = 255;
    let b: u8 = 1;
    let c = a.wrapping_add(b);
    println!("{}", c);
}

A 0

B 256

C 1

D Compilation error

💡 Hint

u8 can only hold values from 0 to 255. Wrapping addition wraps around on overflow.

Adding 255 + 1 overflows u8 and wraps to 0 using wrapping_add.

🔧 Debug

advanced

What error does this Rust code produce?

Analyze the code and select the error it will cause when compiled.

Rust

fn main() {
    let x: i32 = 5.0;
    println!("{}", x);
}

A No error, prints 5

B Syntax error

C Runtime panic

D Type mismatch error

💡 Hint

Check the type assigned to x and the value given.

You cannot assign a floating-point value (5.0) to an integer variable (i32) without explicit casting.

📝 Syntax

advanced

Which option correctly declares a character scalar in Rust?

Select the correct Rust code that declares a variable `ch` as a character with value 'R'.

A let ch = 'R';

B let ch: char = "R";

C let ch: char = 'R';

D let ch: character = 'R';

💡 Hint

Characters use single quotes and the type is `char`.

Option C uses the correct type `char` and single quotes for a character literal.

🚀 Application

expert

How many bytes does this Rust scalar type occupy?

In Rust, how many bytes does the scalar type `f64` occupy in memory?

A 8 bytes

B 16 bytes

C Depends on the system architecture

D 4 bytes

💡 Hint

f64 is a 64-bit floating point number.

f64 is a 64-bit (8 bytes) floating point scalar type in Rust, fixed size regardless of architecture.

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