Relational operators in Rust - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of chained relational operators

What is the output of this Rust code snippet?

Rust

fn main() {
    let a = 5;
    let b = 10;
    let c = 15;
    println!("{}", a < b && b < c);
}

A Compilation error

B false

C true

D Runtime panic

💡 Hint

Think about how logical AND works with relational operators.

The expression a < b && b < c checks if a is less than b AND b is less than c. Both are true, so the output is true.

❓ Predict Output

intermediate

Result of comparing floating-point numbers

What will this Rust program print?

Rust

fn main() {
    let x = 0.1 + 0.2;
    let y = 0.3;
    println!("{}", x == y);
}

A Compilation error

B false

C true

D Runtime panic

💡 Hint

Floating-point arithmetic can be tricky due to precision.

Due to floating-point precision, 0.1 + 0.2 is not exactly equal to 0.3, so the comparison returns false.

❓ Predict Output

advanced

Output of relational operators with characters

What does this Rust code print?

Rust

fn main() {
    let ch1 = 'a';
    let ch2 = 'A';
    println!("{}", ch1 > ch2);
}

A Runtime panic

B false

C Compilation error

D true

💡 Hint

Characters are compared by their Unicode values.

The Unicode value of 'a' is greater than 'A', so the expression ch1 > ch2 is true.

❓ Predict Output

advanced

Relational operator with references

What is the output of this Rust program?

Rust

fn main() {
    let x = 10;
    let y = 20;
    let px = &x;
    let py = &y;
    println!("{}", px < py);
}

A Compilation error

B false

C true

D Runtime panic

💡 Hint

Check if Rust allows direct comparison of references with < operator.

Rust does not implement the < operator for references to integers directly, so this code causes a compilation error.

🧠 Conceptual

expert

Understanding relational operator precedence

Consider this Rust expression: 3 + 4 > 5 && 2 * 2 == 4. What is the value of this expression?

A true

B false

C Compilation error

D Runtime panic

💡 Hint

Remember operator precedence: arithmetic before relational, then logical.

3 + 4 is 7, which is greater than 5 (true). 2 * 2 is 4, equal to 4 (true). true && true is true.

Practice

1. Which of the following relational operators in Rust checks if two values are not equal?

easy

A. !=

B. ==

C. <=

D. >=

Solution

1. Step 1: Understand the meaning of relational operators

   Relational operators compare two values and return true or false based on the comparison.

2. Step 2: Identify the operator for 'not equal'

   The operator '!=' means 'not equal to' in Rust.

3. Final Answer:

   != -> Option A

4. Quick Check:

   Not equal operator = != [OK]

Hint: Remember '!=' means not equal in most languages [OK]

Common Mistakes:

• Confusing '!=' with '=='
• Using '<>' which is not valid in Rust
• Mixing up '<=' and '>='

2. Which of the following is the correct syntax to check if variable a is greater than or equal to variable b in Rust?

easy

A. a =>= b

B. a => b

C. a =< b

D. a >= b

Solution

1. Step 1: Recall Rust relational operator syntax

   Rust uses '>=' to check if left value is greater than or equal to right value.

2. Step 2: Identify correct syntax among options

   Only 'a >= b' matches the correct Rust syntax.

3. Final Answer:

   a >= b -> Option D

4. Quick Check:

   Greater or equal operator = >= [OK]

Hint: Greater or equal is '>=' not '=>' [OK]

Common Mistakes:

• Using '=>' instead of '>='
• Swapping '=' and '<' in operators
• Confusing assignment '=' with comparison

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

let x = 10;
let y = 20;
println!("{}", x < y);

medium

A. true

B. 20

C. 10

D. false

Solution

1. Step 1: Understand the comparison operation

   The code compares if x (10) is less than y (20), which is true.

2. Step 2: Determine the printed output

   Since the condition is true, the printed output will be 'true'.

3. Final Answer:

   true -> Option A

4. Quick Check:

   10 < 20 = true [OK]

Hint: Compare values carefully; 10 is less than 20 [OK]

Common Mistakes:

• Confusing output with variable values
• Thinking it prints the smaller number
• Mixing up < and > operators

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

let a = 5;
let b = 10;
if a <> b {
    println!("Not equal");
}

medium

A. Variables a and b must be mutable

B. The operator '<>' is invalid in Rust

C. Missing semicolon after println!

D. The if statement needs parentheses

Solution

1. Step 1: Check the relational operator used

   The operator '<>' is not a valid relational operator in Rust.

2. Step 2: Confirm correct operator for not equal

   Rust uses '!=' to check if two values are not equal.

3. Final Answer:

   The operator '<>' is invalid in Rust -> Option B

4. Quick Check:

   Not equal operator = !=, not <> [OK]

Hint: Use '!=' for not equal, not '<>' [OK]

Common Mistakes:

• Using '<>' from other languages
• Forgetting Rust requires '!='
• Assuming parentheses needed in if condition

5. Given a list of integers, which Rust expression correctly checks if all elements are greater than 0 using relational operators?

hard

A. numbers.iter().filter(|&x| x > 0)

B. numbers.iter().any(|&x| x > 0)

C. numbers.iter().all(|&x| x > 0)

D. numbers.iter().map(|&x| x > 0)

Solution

1. Step 1: Understand the requirement

   We want to check if all elements in the list are greater than 0.

2. Step 2: Identify the correct iterator method

   'all' returns true only if every element satisfies the condition x > 0.

3. Step 3: Confirm the closure syntax

   The closure '|&x| x > 0' correctly compares each element to 0.

4. Final Answer:

   numbers.iter().all(|&x| x > 0) -> Option C

5. Quick Check:

   Check all elements > 0 with 'all' method [OK]

Hint: Use 'all' to check every element meets condition [OK]

Common Mistakes:

• Using 'any' which checks only one element
• Using 'filter' which returns iterator, not bool
• Using 'map' which transforms elements, not checks