Ternary operator 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. It uses the syntax: condition ? true_value : false_value.

beginner

How does the ternary operator work in Ruby?

It checks the condition before the ?. If true, it returns the value after ? and before :. If false, it returns the value after :.

beginner

Rewrite this if-else using a ternary operator:

if age >= 18
  status = 'adult'
else
  status = 'minor'
end

status = age >= 18 ? 'adult' : 'minor'

intermediate

Can the ternary operator be nested in Ruby?

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

beginner

What is a common use case for the ternary operator?

It is used for simple decisions to assign a value quickly without writing multiple lines of if-else statements.

What does this Ruby code return?

5 > 3 ? 'yes' : 'no'

A 'no'

B 5

C 'yes'

D 3

Since 5 is greater than 3, the condition is true, so it returns 'yes'.

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

A ?

B !

C ;

D :

The colon ':' separates the true part (after '?') and the false part.

What is the output of this code?

puts (10 == 10 ? 'Equal' : 'Not equal')

A Not equal

B Equal

C 10

D Error

10 == 10 is true, so it prints 'Equal'.

Is this a valid ternary operator usage in Ruby?

result = condition ? do_something : do_something_else

A Yes, it's valid

B No, syntax error

C Only if condition is true

D Only if condition is false

This is the correct syntax for a ternary operator.

Why might you avoid nesting ternary operators?

A They make code hard to read

B They run slower

C They cause syntax errors

D They are not supported in Ruby

Nesting ternary operators can make code confusing and hard to maintain.

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

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

Describe a situation where using a ternary operator is better than an if-else statement.

When you want to assign a value quickly based on a condition.

Practice

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

easy

A. It chooses one of two values based on a condition.

B. It creates a loop that runs twice.

C. It defines a new method.

D. It comments out a line of code.

Solution

1. Step 1: Understand the ternary operator syntax

   The ternary operator uses a condition followed by a question mark, then the value if true, a colon, and the value if false.

2. Step 2: Identify its purpose

   This syntax means it picks one of two values depending on whether the condition is true or false.

3. Final Answer:

   It chooses one of two values based on a condition. -> Option A

4. Quick Check:

   condition ? true_value : false_value = chooses value [OK]

Hint: Remember: condition ? true : false picks one value fast [OK]

Common Mistakes:

• Thinking it creates loops
• Confusing it with method definitions
• Believing it comments code

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 the ternary operator format

   The correct format is condition followed by a question mark, then the true value, a colon, and the false value.

2. Step 2: Compare options

   Only condition ? value_if_true : value_if_false matches this exact syntax; others misuse punctuation or order.

3. Final Answer:

   condition ? value_if_true : value_if_false -> Option A

4. Quick Check:

   Syntax = condition ? true : false [OK]

Hint: Question mark then colon separate true and false parts [OK]

Common Mistakes:

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

3. What is the output of this Ruby code?

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

medium

A. Minor

B. 20

C. SyntaxError

D. Adult

Solution

1. Step 1: Evaluate the condition age >= 18

   Since age is 20, which is greater than or equal to 18, the condition is true.

2. Step 2: Apply the ternary operator

   Because the condition is true, message is assigned "Adult".

3. Final Answer:

   Adult -> Option D

4. Quick Check:

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

Hint: Check condition result first, then pick true or false value [OK]

Common Mistakes:

• Choosing the false value by mistake
• Printing the variable instead of its value
• Confusing syntax errors

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

score = 75
result = score > 60 ? "Pass" "Fail"
puts result

medium

A. Wrong variable name

B. Missing colon between true and false values

C. Missing question mark after condition

D. Using double quotes incorrectly

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 : false [OK]

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

Common Mistakes:

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

5. You want to assign a variable status based on a number n: if n is positive, assign "Positive"; if zero, assign "Zero"; else assign "Negative". Which Ruby code using ternary operators is correct?

hard

A. status = n > 0 ? "Positive" : n == 0 ? "Zero" "Negative"

B. status = n > 0 ? "Positive" : "Zero" ? n == 0 : "Negative"

C. status = n > 0 ? "Positive" : (n == 0 ? "Zero" : "Negative")

D. status = (n > 0 ? "Positive" : "Zero") ? n == 0 : "Negative"

Solution

1. Step 1: Understand nested ternary operator usage

   To handle three cases, nest one ternary inside the false part of another, using parentheses for clarity.

2. Step 2: Analyze each option

   status = n > 0 ? "Positive" : (n == 0 ? "Zero" : "Negative") correctly nests the second ternary inside parentheses, ensuring proper evaluation order.

3. Final Answer:

   status = n > 0 ? "Positive" : (n == 0 ? "Zero" : "Negative") -> Option C

4. Quick Check:

   Nested ternary with parentheses = correct [OK]

Hint: Use parentheses to nest ternary operators clearly [OK]

Common Mistakes:

• Missing parentheses causing wrong evaluation
• Misplacing question marks and colons
• Confusing order of conditions