Relational operators in Rust - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are relational operators in Rust?

Relational operators compare two values and return a boolean (true or false) based on the comparison.

beginner

What does the operator < mean in Rust?

The < operator means "less than". It checks if the value on the left is smaller than the value on the right.

beginner

How do you check if two values are equal in Rust?

Use the == operator to check if two values are equal. It returns true if they are the same, false otherwise.

beginner

What is the difference between == and != operators?

== checks if two values are equal, while != checks if two values are not equal.

beginner

What will the expression 5 >= 3 return in Rust?

It will return true because 5 is greater than or equal to 3.

Which operator checks if a value is greater than another in Rust?

A !=

B <=

C >

D ==

The > operator checks if the left value is greater than the right value.

What does the expression 4 != 4 evaluate to?

A true

B false

C error

D 4

4 != 4 means '4 is not equal to 4', which is false.

Which operator would you use to check if two values are equal?

A ==

B <

C !=

D >=

The == operator checks if two values are equal.

What is the result of 7 < 10 in Rust?

A true

B 7

C false

D error

7 is less than 10, so the expression returns true.

Which operator means 'greater than or equal to'?

A <=

B !=

C ==

D >=

The >= operator means 'greater than or equal to'.

Explain what relational operators are and list the common ones in Rust.

Think about how you compare numbers or values in everyday life.

Describe how you would use relational operators to compare two numbers in Rust and what type of value the comparison returns.

Remember, comparisons answer yes/no questions.

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