Guard clauses pattern in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of method using guard clauses

What is the output of this Ruby method when called with the argument 5?

Ruby

def check_number(num)
  return "Too small" if num < 3
  return "Too large" if num > 10
  "Just right"
end

puts check_number(5)

A Just right

B Too large

C Too small

D nil

💡 Hint

Look at the conditions and see which guard clause applies for 5.

The method returns early if the number is less than 3 or greater than 10. Since 5 is between 3 and 10, it reaches the last line returning "Just right".

❓ Predict Output

intermediate

Return value with multiple guard clauses

What will this Ruby method return when called with the argument 0?

Ruby

def status_code(code)
  return "Error" if code < 0
  return "Success" if code == 0
  "Unknown"
end

puts status_code(0)

A Error

B Unknown

C Success

D nil

💡 Hint

Check which guard clause matches the input 0.

The method returns "Success" immediately if the code equals 0, so it does not reach the last line.

🔧 Debug

advanced

Identify the error in guard clause usage

What error will this Ruby code raise when executed?

Ruby

def process(value)
  return "No value" unless value
  return "Zero" if value == 0
  value * 2
end

puts process(nil)

A NoMethodError

B TypeError

C ArgumentError

D No error, outputs "No value"

💡 Hint

Check the guard clause with 'unless value' and what happens with nil.

The guard clause returns "No value" immediately if value is nil (which is falsey), so no error occurs.

❓ Predict Output

advanced

Output of method with nested guard clauses

What is the output of this Ruby method when called with argument 15?

Ruby

def evaluate(num)
  return "Negative" if num < 0
  return "Small" if num < 10
  return "Medium" if num < 20
  "Large"
end

puts evaluate(15)

A Medium

B Negative

C Small

D Large

💡 Hint

Check each guard clause in order for 15.

15 is not less than 0 or 10, but it is less than 20, so the method returns "Medium".

❓ Predict Output

expert

Return value with complex guard clauses and side effects

What will be printed when this Ruby code runs?

Ruby

def complex_check(x)
  return "Negative" if x < 0
  puts "Checking zero"
  return "Zero" if x == 0
  return "Positive" if x > 0
  "Unknown"
end

result = complex_check(0)
puts result

A

Negative
Negative

B

Checking zero
Zero

C

Zero
Zero

D

Checking zero
Positive

💡 Hint

Notice the puts inside the method before the guard clause for zero.

When x is 0, the method prints "Checking zero" then returns "Zero", so the output is two lines: first the printed string, then the returned string printed outside.

Practice

1. What is the main purpose of using guard clauses in Ruby methods?

easy

A. To exit a method early when a condition is not met

B. To create loops inside methods

C. To define variables at the start of a method

D. To delay method execution until a condition is true

Solution

1. Step 1: Understand guard clause purpose

   Guard clauses are used to stop method execution early if certain conditions fail.

2. Step 2: Compare options with guard clause use

   Only To exit a method early when a condition is not met describes exiting early based on a condition, which matches guard clauses.

3. Final Answer:

   To exit a method early when a condition is not met -> Option A

4. Quick Check:

   Guard clauses = early exit [OK]

Hint: Guard clauses stop method early on bad conditions [OK]

Common Mistakes:

• Confusing guard clauses with loops
• Thinking guard clauses delay execution
• Assuming guard clauses define variables

2. Which of the following is the correct syntax for a guard clause in Ruby to return nil if user is nil?

easy

A. user.nil? return nil

B. if user.nil? then return nil end

C. return nil if user.nil?

D. return nil unless user.nil?

Solution

1. Step 1: Identify correct guard clause syntax

   Ruby guard clauses use return value if condition format.

2. Step 2: Check each option

   return nil if user.nil? matches the correct syntax: return nil if user.nil?. if user.nil? then return nil end is verbose but valid Ruby, not a guard clause style. return nil unless user.nil? returns nil unless user is nil, which is opposite logic. user.nil? return nil is invalid syntax.

3. Final Answer:

   return nil if user.nil? -> Option C

4. Quick Check:

   Guard clause syntax = return value if condition [OK]

Hint: Use 'return value if condition' for guard clauses [OK]

Common Mistakes:

• Using unless instead of if with opposite logic
• Writing invalid syntax without 'if'
• Confusing guard clause with full if-end block

3. What will be the output of the following Ruby code?

def check_age(age)
  return "Too young" if age < 18
  "Welcome"
end

puts check_age(16)
puts check_age(20)

medium

A. Welcome\nWelcome

B. Welcome\nToo young

C. Too young\nToo young

D. Too young\nWelcome

Solution

1. Step 1: Analyze method behavior for age 16

   Since 16 < 18, the guard clause triggers and returns "Too young" immediately.

2. Step 2: Analyze method behavior for age 20

   Since 20 >= 18, guard clause is skipped and method returns "Welcome".

3. Final Answer:

   Too young\nWelcome -> Option D

4. Quick Check:

   Guard clause triggers only if age < 18 [OK]

Hint: Guard clause returns early if condition true [OK]

Common Mistakes:

• Assuming method always returns 'Welcome'
• Mixing up output order
• Ignoring guard clause effect

4. Identify the error in this Ruby method using a guard clause:

def greet(name)
  return "No name provided" if name = nil
  "Hello, #{name}!"
end

medium

A. Incorrect string interpolation syntax

B. Using assignment (=) instead of comparison (==) in guard clause

C. Missing else statement after guard clause

D. Guard clause should be after the greeting line

Solution

1. Step 1: Check guard clause condition

   The guard clause uses name = nil, which assigns nil to name instead of comparing.

2. Step 2: Identify correct comparison operator

   To check if name is nil, it should use name == nil or better name.nil?.

3. Final Answer:

   Using assignment (=) instead of comparison (==) in guard clause -> Option B

4. Quick Check:

   Use '==' or '.nil?' for comparisons, not '=' [OK]

Hint: Use '==' to compare, '=' assigns value [OK]

Common Mistakes:

• Confusing '=' with '==' in conditions
• Thinking else is required after guard clause
• Misusing string interpolation syntax

5. You want to write a Ruby method process_order(order) that returns "Invalid order" immediately if order is nil or empty. Otherwise, it returns "Processing order". Which is the best way to write this using guard clauses?

hard

A. return "Invalid order" if order.nil? || order.empty?
"Processing order"

B. if order.nil? || order.empty?
return "Invalid order"
else
"Processing order"
end

C. unless order.nil? && order.empty?
return "Invalid order"
end
"Processing order"

D. return "Invalid order" unless order.nil? || order.empty?
"Processing order"

Solution

1. Step 1: Identify correct guard clause condition

   The method should return early if order is nil OR empty, so condition is order.nil? || order.empty?.

2. Step 2: Check each option's logic and syntax

   return "Invalid order" if order.nil? || order.empty? "Processing order" uses a guard clause with correct condition and returns "Invalid order" early, then returns "Processing order" otherwise. if order.nil? || order.empty? return "Invalid order" else "Processing order" end uses if-else but not guard clause style. unless order.nil? && order.empty? return "Invalid order" end "Processing order" uses unless with && which is incorrect logic. return "Invalid order" unless order.nil? || order.empty? "Processing order" uses unless with || but negated logic, causing wrong behavior.

3. Final Answer:

   return "Invalid order" if order.nil? || order.empty? "Processing order" -> Option A

4. Quick Check:

   Guard clause with correct condition = return "Invalid order" if order.nil? || order.empty? "Processing order" [OK]

Hint: Use 'return value if condition' with correct OR logic [OK]

Common Mistakes:

• Using && instead of || in condition
• Negating condition incorrectly with unless
• Not returning early with guard clause