Comparison operators in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of chained comparison with integers

What is the output of this Ruby code?

Ruby

result = 3 < 5 && 5 < 7
puts result

A SyntaxError

B true

C false

D nil

💡 Hint

Remember that && checks if both sides are true.

The expression checks if 3 is less than 5 AND 5 is less than 7. Both are true, so the result is true.

❓ Predict Output

intermediate

Output of spaceship operator <=> with strings

What will this Ruby code output?

Ruby

puts 'apple' <=> 'banana'

A -1

B 0

C 1

D nil

💡 Hint

The spaceship operator returns -1 if left is less than right.

Since 'apple' comes before 'banana' alphabetically, the operator returns -1.

❓ Predict Output

advanced

Result of comparing different types with == and eql?

What is the output of this Ruby code?

Ruby

a = 5
b = 5.0
puts a == b
puts a.eql?(b)

A

true
false

B

false
false

C

true
true

D

false
true

💡 Hint

== compares values, eql? compares both value and type.

5 == 5.0 is true because values are equal, but 5.eql?(5.0) is false because types differ (Integer vs Float).

❓ Predict Output

advanced

Output of combined comparison with case statement

What will this Ruby code output?

Ruby

score = 85
case score
when 90..100 then puts 'A'
when 80...90 then puts 'B'
else puts 'F'
end

A SyntaxError

B A

C F

D B

💡 Hint

Check which range includes 85.

85 is in the range 80...90 (80 to 89), so it prints 'B'.

🧠 Conceptual

expert

Behavior of <=> operator with nil values

What error or output results from this Ruby code?

Ruby

puts nil <=> 5

A TypeError

B ArgumentError

C nil

D false

💡 Hint

The spaceship operator returns nil if values are not comparable.

Comparing nil with a number using <=> returns nil because they are not comparable.

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