Comparison operators in Ruby - Mini Project: Build & Apply

Comparison operators

📖 Scenario: You are helping a store manager compare product prices to decide which items are cheaper or more expensive.

🎯 Goal: You will write a Ruby program that uses comparison operators to compare product prices and print the results.

📋 What You'll Learn

Create a hash with product names and their prices

Create a variable with a price threshold

Use comparison operators to check if each product price is less than, equal to, or greater than the threshold

Print the comparison results

💡 Why This Matters

🌍 Real World

Stores often compare product prices to decide discounts or promotions.

💼 Career

Understanding comparison operators is essential for decision-making logic in programming jobs.

1

Create the product prices hash

Create a hash called products with these exact entries: 'apple' => 100, 'banana' => 50, 'cherry' => 75

Ruby

# Create the products hash with prices
# Your code here

Hint

Use curly braces {} to create a hash and separate keys and values with =>.

2

Set the price threshold

Create a variable called threshold and set it to 70

Ruby

products = { 'apple' => 100, 'banana' => 50, 'cherry' => 75 }
# Create the threshold variable
# Your code here

Hint

Just assign the number 70 to the variable threshold.

3

Compare product prices to the threshold

Use a products.each loop with variables product and price to compare each price with threshold using <, ==, and > operators. Inside the loop, create a variable result that stores the string "less than" if price < threshold, "equal to" if price == threshold, or "greater than" if price > threshold.

Ruby

products = { 'apple' => 100, 'banana' => 50, 'cherry' => 75 }
threshold = 70
# Loop through products and compare prices
# Your code here

Hint

Use if, elsif, and else inside the loop to set result.

4

Print the comparison results

Inside the products.each loop, add a puts statement to print the message: "The price of #{product} is #{result} the threshold."

Ruby

products = { 'apple' => 100, 'banana' => 50, 'cherry' => 75 }
threshold = 70
products.each do |product, price|
  result = if price < threshold
    "less than"
  elsif price == threshold
    "equal to"
  else
    "greater than"
  end
  # Print the comparison message
  # Your code here
end

Hint

Use puts with string interpolation to print the message inside the loop.

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