Comparison operators in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the == operator do in Ruby?

The == operator checks if two values are equal. It returns true if they are the same, otherwise false.

intermediate

What is the difference between == and === in Ruby?

== checks if two objects are equal in value. === is used mainly in case statements to test if an object matches a condition or belongs to a class.

beginner

What does the < operator do?

The < operator checks if the value on the left is less than the value on the right. It returns true if yes, otherwise false.

beginner

How does the != operator work?

The != operator checks if two values are not equal. It returns true if they are different, otherwise false.

beginner

What will 5 >= 3 return in Ruby?

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

Which operator checks if two values are exactly equal in Ruby?

A !=

B =

C ==

D <

The == operator checks if two values are equal.

What does the != operator do?

A Checks if two values are not equal

B Checks if two values are equal

C Assigns a value

D Checks if left is less than right

The != operator returns true if two values are not equal.

Which operator is used in Ruby case statements to test matching?

A ==

B !=

C <=

D ===

The === operator is used in case statements for matching.

What will 4 < 2 return?

A true

B false

C nil

D error

4 is not less than 2, so it returns false.

Which operator checks if left value is greater than or equal to right value?

A >=

B !=

C ==

D <=

The >= operator checks if left is greater than or equal to right.

Explain how to compare two numbers to check if one is less than the other in Ruby.

Think about the symbol that means 'less than'.

Describe the difference between == and === operators in Ruby.

One is for simple equality, the other is for pattern matching.

Practice

1. Which of the following comparison operators in Ruby checks if two values are equal?

easy

A. ==

B. =

C. !=

D. >

Solution

1. Step 1: Understand the purpose of each operator

   == checks equality, = assigns values, != checks inequality, and > checks if left is greater than right.

2. Step 2: Identify the equality operator

   The operator that compares two values for equality is ==.

3. Final Answer:

   == -> Option A

4. Quick Check:

   Equality operator = == [OK]

Hint: Equality uses double equals (==), not single equals (=) [OK]

Common Mistakes:

• Confusing assignment (=) with equality (==)
• Using != instead of ==
• Thinking > checks equality

2. Which of the following is the correct syntax to check if variable a is not equal to variable b in Ruby?

easy

A. a !== b

B. a =! b

C. a <> b

D. a != b

Solution

1. Step 1: Recall Ruby's not equal operator

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

2. Step 2: Check each option's syntax

   a != b is correct. a =! b is invalid syntax. a <> b is not Ruby syntax. a !== b is JavaScript syntax, not Ruby.

3. Final Answer:

   a != b -> Option D

4. Quick Check:

   Not equal operator = != [OK]

Hint: Not equal in Ruby is !=, not =! or !== [OK]

Common Mistakes:

• Using =! instead of !=
• Using !== which is JavaScript, not Ruby
• Using <> which is invalid in Ruby

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

a = 5
b = 10
puts a < b

medium

A. true

B. false

C. 5

D. 10

Solution

1. Step 1: Understand the comparison

   The code compares if a (5) is less than b (10).

2. Step 2: Evaluate the comparison

   Since 5 is less than 10, the expression a < b is true.

3. Final Answer:

   true -> Option A

4. Quick Check:

   5 < 10 = true [OK]

Hint: Less than is <, returns true or false [OK]

Common Mistakes:

• Confusing output with variable values
• Expecting numeric output instead of boolean
• Mixing up < and > operators

4. Identify the error in the following Ruby code:

if x = 10
  puts "x is 10"
end

medium

A. Variable x is not declared

B. Missing end keyword

C. Should use == to compare, not =

D. puts syntax is wrong

Solution

1. Step 1: Analyze the if condition

   The code uses = which assigns 10 to x, not compares.

2. Step 2: Correct the comparison operator

   To check if x equals 10, use == instead of =.

3. Final Answer:

   Should use == to compare, not = -> Option C

4. Quick Check:

   Comparison needs ==, = is assignment [OK]

Hint: Use == for comparison, = is for assignment [OK]

Common Mistakes:

• Using = instead of ==
• Thinking missing end keyword causes error
• Assuming variable must be declared before use

5. You want to check if a number n is between 10 and 20 inclusive in Ruby. Which expression correctly uses comparison operators to do this?

hard

A. n > 10 || n < 20

B. n >= 10 && n <= 20

C. 10 <= n <= 20

D. n == 10 && n == 20

Solution

1. Step 1: Understand the range check

   We want n to be at least 10 and at most 20, so both conditions must be true.

2. Step 2: Evaluate each option

   n >= 10 && n <= 20 uses n >= 10 && n <= 20, which correctly checks both limits.
   10 <= n <= 20 uses chained comparison which is invalid in Ruby.
   n > 10 || n < 20 uses OR (||), which allows values outside the range.
   n == 10 && n == 20 checks if n equals both 10 and 20 simultaneously, which is impossible.

3. Final Answer:

   n >= 10 && n <= 20 -> Option B

4. Quick Check:

   Use && to combine two comparisons [OK]

Hint: Use && to combine two comparisons for range checks [OK]

Common Mistakes:

• Trying chained comparisons like 10 <= n <= 20
• Using || instead of && for range
• Checking equality to both ends simultaneously