Integer types in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a 32-bit signed integer variable named num with the value 10.

Rust

let num: [1] = 10;

Drag options to blanks, or click blank then click option'

Af32

Bu32

Ci32

Dbool

Attempts:

3 left

💡 Hint

Common Mistakes

Using u32 which is unsigned and might not be intended here.

Using floating point types like f32 for integers.

The i32 type is a 32-bit signed integer in Rust, suitable for storing the value 10.

2fill in blank

medium

Complete the code to declare an unsigned 8-bit integer variable named age with the value 25.

Rust

let age: [1] = 25;

Drag options to blanks, or click blank then click option'

Au8

Bi16

Cbool

Di8

Attempts:

3 left

💡 Hint

Common Mistakes

Using signed types like i8 which allow negative numbers.

Using boolean type bool which is not numeric.

The u8 type is an 8-bit unsigned integer, perfect for small positive numbers like 25.

3fill in blank

hard

Fix the error in the code by choosing the correct integer type for the variable count initialized with 1000.

Rust

let count: [1] = 1000;

Drag options to blanks, or click blank then click option'

Ai16

Bu8

Ci8

Dbool

Attempts:

3 left

💡 Hint

Common Mistakes

Using i8 or u8 which are too small for 1000.

Using bool which is not numeric.

The value 1000 is too large for i8 or u8 which only hold up to 127 and 255 respectively. i16 can hold values up to 32767.

4fill in blank

hard

Fill both blanks to create a dictionary that maps numbers to their squares for numbers 1 to 3, using the correct integer types and operators.

Rust

let squares = std::collections::HashMap::from([(1[1] 3, 1[2] 3)]);

Drag options to blanks, or click blank then click option'

A..=

B*

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using .. which excludes the last number.

Using addition or subtraction instead of multiplication for squares.

The ..= operator creates an inclusive range from 1 to 3. The * operator calculates the square of each number.

5fill in blank

hard

Fill both blanks to create a HashMap that stores the length of each word only if the length is greater than 3.

Rust

let lengths = words.iter().filter(|&word| word.len() [1] 3).map(|word| (word.to_string(), word.len() [2] ,)).collect::<std::collections::HashMap<_, _>>();

Drag options to blanks, or click blank then click option'

A>

B-

C,

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect comparison operators in filter.

Not separating tuple elements with a comma.

Using addition instead of subtraction for length adjustment.

The filter uses > to select words longer than 3. The map creates tuples with the word and its length minus 1, separated by a comma.

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