Ternary operator usage in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the ternary operator in Ruby?

The ternary operator is a short way to write an if-else statement in one line. It uses the syntax: condition ? true_value : false_value.

beginner

How does the ternary operator improve code readability?

It makes simple if-else decisions concise and easy to read by reducing multiple lines into one line.

beginner

Example: What does this Ruby code return?
age = 20
result = age >= 18 ? 'Adult' : 'Minor'

It returns 'Adult' because the condition age >= 18 is true.

intermediate

Can the ternary operator be nested in Ruby?

Yes, but nesting ternary operators can make code hard to read. It's better to use regular if-else for complex conditions.

beginner

What is the difference between ternary operator and if-else in Ruby?

Ternary operator is a compact form for simple if-else statements. If-else can handle multiple lines and complex logic.

What symbol separates the true and false parts in a Ruby ternary operator?

A :

B ?

C ;

D ->

The colon ':' separates the true and false expressions in the ternary operator.

Which of these is a correct Ruby ternary operator syntax?

A condition if true_value else false_value

B condition : true_value ? false_value

C condition ? true_value ? false_value

D condition ? true_value : false_value

The correct syntax is condition ? true_value : false_value.

What will this Ruby code output?
puts 5 > 10 ? 'Yes' : 'No'

A 5 > 10

B Yes

C No

D Error

Since 5 is not greater than 10, the condition is false, so it outputs 'No'.

Is it good practice to use ternary operators for complex multiple conditions?

A Yes, always

B No, it reduces readability

C Only if nested

D Only in loops

Using ternary operators for complex conditions makes code hard to read; use if-else instead.

What does the ternary operator return if the condition is true?

A The expression after '?'

B The expression after ':'

C The condition itself

D Nothing

If the condition is true, the ternary operator returns the expression after the '?'.

Explain how the ternary operator works in Ruby and give a simple example.

Think of it as a short if-else in one line.

When should you avoid using the ternary operator in Ruby?

Consider how easy it is to understand your code.

Practice

1. What does the ternary operator condition ? value_if_true : value_if_false do in Ruby?

easy

A. It chooses one of two values based on the condition's truth.

B. It creates a loop that runs twice.

C. It defines a new method with two parameters.

D. It comments out the code after the colon.

Solution

1. Step 1: Understand the ternary operator format

   The ternary operator uses a condition followed by a question mark, then two values separated by a colon.

2. Step 2: Identify its purpose

   It returns the first value if the condition is true, otherwise the second value.

3. Final Answer:

   It chooses one of two values based on the condition's truth. -> Option A

4. Quick Check:

   condition ? true_value : false_value = chooses value [OK]

Hint: Think: condition true? pick first value, else second [OK]

Common Mistakes:

• Confusing ternary with loops
• Thinking it defines methods
• Misunderstanding the colon as comment

2. Which of the following is the correct syntax for a ternary operator in Ruby?

easy

A. condition ? value_if_true : value_if_false

B. condition : value_if_true ? value_if_false

C. condition ? value_if_true ; value_if_false

D. condition ? value_if_true, value_if_false

Solution

1. Step 1: Recall ternary operator syntax

   The correct syntax places a question mark after the condition, then the true value, a colon, then the false value.

2. Step 2: Compare options

   Only condition ? value_if_true : value_if_false matches the correct format: condition ? true_value : false_value.

3. Final Answer:

   condition ? value_if_true : value_if_false -> Option A

4. Quick Check:

   Syntax = condition ? true : false [OK]

Hint: Remember: question mark before true, colon before false [OK]

Common Mistakes:

• Swapping question mark and colon
• Using semicolon instead of colon
• Separating values with comma

3. What is the output of this Ruby code?

age = 20
puts age >= 18 ? "Adult" : "Minor"

medium

A. Minor

B. 20

C. SyntaxError

D. Adult

Solution

1. Step 1: Evaluate the condition

   The condition age >= 18 is true because age is 20.

2. Step 2: Apply ternary operator

   Since the condition is true, the expression returns "Adult".

3. Final Answer:

   Adult -> Option D

4. Quick Check:

   20 >= 18 ? "Adult" : "Minor" = "Adult" [OK]

Hint: Check condition true? pick first value, else second [OK]

Common Mistakes:

• Choosing the false value by mistake
• Printing the variable instead of result
• Expecting syntax error

4. Identify the error in this Ruby code using a ternary operator:

score = 85
result = score > 60 ? "Pass" "Fail"
puts result

medium

A. Missing question mark after condition

B. Missing colon between true and false values

C. Ternary operator cannot be used with strings

D. Wrong variable name 'score'

Solution

1. Step 1: Check ternary operator syntax

   The ternary operator requires a colon between the true and false values.

2. Step 2: Identify missing colon

   The code has "Pass" "Fail" without a colon, causing a syntax error.

3. Final Answer:

   Missing colon between true and false values -> Option B

4. Quick Check:

   Syntax = condition ? true_value : false_value [OK]

Hint: Always put colon between true and false parts [OK]

Common Mistakes:

• Omitting colon
• Using comma instead of colon
• Forgetting question mark

5. Given this Ruby code, what will be the output?

values = [0, 1, nil, 5]
results = values.map { |v| v ? "Yes" : "No" }
puts results.inspect

hard

A. ["No", "Yes", "No", "Yes"]

B. ["No", "No", "No", "No"]

C. ["Yes", "Yes", "No", "Yes"]

D. ["Yes", "No", "Yes", "No"]

Solution

1. Step 1: Understand truthiness in Ruby

   In Ruby, 0 and 1 are truthy, nil is falsy.

2. Step 2: Apply ternary operator to each element

   For each value: 0 (truthy) -> "Yes", 1 (truthy) -> "Yes", nil (falsy) -> "No", 5 (truthy) -> "Yes".

3. Step 3: Check mapped results

   The results array is ["Yes", "Yes", "No", "Yes"].

4. Final Answer:

   ["Yes", "Yes", "No", "Yes"] -> Option C

5. Quick Check:

   Truthy values = "Yes", nil = "No" [OK]

Hint: Remember: only nil and false are falsey in Ruby [OK]

Common Mistakes:

• Thinking 0 is falsy
• Confusing nil with false
• Misreading map block