Comparison operators in Ruby - Step-by-Step Execution

Concept Flow - Comparison operators

Start

↓

Evaluate Left Value

↓

Evaluate Right Value

↓

Apply Comparison Operator

↓

Result: true or false

↓

Use Result in Condition or Output

↓

End

The program compares two values using a comparison operator and produces true or false as the result.

Execution Sample

Ruby

a = 5
b = 3
result = a > b
puts result

This code compares if a is greater than b and prints the result.

Execution Table

Step	Action	Evaluation	Result
1	Assign a = 5	a = 5	5
2	Assign b = 3	b = 3	3
3	Compare a > b	5 > 3	true
4	Assign result = true	result = true	true
5	Print result	puts result	true

💡 Program ends after printing the comparison result.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
a	nil	5	5	5	5	5
b	nil	nil	3	3	3	3
result	nil	nil	nil	nil	true	true

Key Moments - 2 Insights

Why does the comparison a > b return true instead of a number?

Because comparison operators in Ruby return a boolean value (true or false), not a numeric result. See step 3 in the execution_table where 5 > 3 evaluates to true.

What happens if we compare two equal values with == operator?

The comparison returns true if both values are equal, otherwise false. This is similar to step 3 but with == instead of >.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'result' after step 4?

A 5

B true

C false

D nil

💡 Hint

Check the 'result' variable value in variable_tracker after step 4.

At which step does the comparison a > b happen?

A Step 3

B Step 2

C Step 4

D Step 5

💡 Hint

Look at the 'Action' column in execution_table for the comparison operation.

If we change b to 7, what would be the result of a > b at step 3?

A true

B nil

C false

D error

💡 Hint

Compare 5 > 7 logically to determine the boolean result.

Concept Snapshot

Comparison operators compare two values and return true or false.
Common operators: ==, !=, >, <, >=, <=.
Used in conditions and expressions.
Example: a > b returns true if a is greater than b.
They do not return numbers, only boolean values.

Full Transcript

This visual execution trace shows how comparison operators work in Ruby. We start by assigning values to variables a and b. Then we compare a > b, which evaluates to true or false. This boolean result is stored in the variable result and printed. The trace shows each step, variable changes, and the final output. Comparison operators always return true or false, not numbers. This helps in making decisions in code.

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