Case with ranges and patterns in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of case with range and pattern matching

What is the output of this Ruby code?

Ruby

score = 85
result = case score
when 90..100 then "Excellent"
when 75..89 then "Good"
when 50..74 then "Pass"
else "Fail"
end
puts result

A Good

B Excellent

C Pass

D Fail

💡 Hint

Check which range 85 falls into.

The variable score is 85, which falls into the range 75..89, so the case returns "Good".

❓ Predict Output

intermediate

Pattern matching with case and array

What will this Ruby code print?

Ruby

value = [1, 2, 3]
case value
in [Integer, Integer, 3]
  puts "Matched pattern"
else
  puts "No match"
end

A No match

B RuntimeError

C SyntaxError

D Matched pattern

💡 Hint

Check if the array matches the pattern with two integers followed by 3.

The array [1, 2, 3] matches the pattern [Integer, Integer, 3], so it prints "Matched pattern".

❓ Predict Output

advanced

Case with pattern matching and variable binding

What is the output of this Ruby code?

Ruby

point = { x: 10, y: 20 }
case point
in { x: 10, y: y_val }
  puts "Y is #{y_val}"
else
  puts "No match"
end

A Y is y_val

B Y is 20

C No match

D SyntaxError

💡 Hint

Look at how y is bound in the pattern.

The pattern matches a hash with x:10 and binds y to y_val, which is 20, so it prints "Y is 20".

❓ Predict Output

advanced

Case with range and pattern matching combined

What will this Ruby code output?

Ruby

value = 7
case value
in 1..5
  puts "Low"
in 6..10
  puts "Medium"
else
  puts "High"
end

A High

B Low

C Medium

D SyntaxError

💡 Hint

Check which range 7 belongs to.

7 is in the range 6..10, so the case prints "Medium".

❓ Predict Output

expert

Complex pattern matching with nested structures

What is the output of this Ruby code?

Ruby

data = { user: { name: "Alice", age: 30 }, status: :active }
case data
in { user: { name: "Alice", age: age_val }, status: :active }
  puts "Active user Alice, age #{age_val}"
else
  puts "No match"
end

A Active user Alice, age 30

B No match

C SyntaxError

D RuntimeError

💡 Hint

Look carefully at the nested hash pattern and variable binding.

The pattern matches the nested hash and binds age to age_val (30), so it prints "Active user Alice, age 30".

Practice

1.

What does the in keyword do inside a case statement in Ruby when used with ranges?

easy

A. It checks if the value falls within the given range.

B. It assigns the range to the value.

C. It creates a new range object.

D. It compares the value for equality with the range.

Solution

1. Step 1: Understand the role of in in case

   The in keyword is used to match a value against a pattern or range inside a case statement.

2. Step 2: Check how it works with ranges

   When used with a range like 1..10, it checks if the value lies within that range.

3. Final Answer:

   It checks if the value falls within the given range. -> Option A

4. Quick Check:

   in with range means value in range [OK]

Hint: Remember: in checks membership in range or pattern [OK]

Common Mistakes:

• Thinking in assigns values instead of matching
• Confusing range equality with membership
• Assuming in creates new objects

2.

Which of the following is the correct syntax to match a number n in the range 5 to 15 inside a case statement using pattern matching?

case n
  in ???
    puts "In range"
  else
    puts "Out of range"
end

easy

A. in (5..15)

B. 5..15

C. 5...15

D. in 5..15

Solution

1. Step 1: Identify correct pattern syntax in in clause

   Inside case, in is followed directly by the pattern, so in 5..15 is correct syntax.

2. Step 2: Check other options for syntax errors

   Options without in or with extra parentheses are invalid syntax in this context.

3. Final Answer:

   in 5..15 -> Option D

4. Quick Check:

   Use in followed by the pattern without extra keywords or parentheses [OK]

Hint: Use in once, then the pattern without extra keywords [OK]

Common Mistakes:

• Writing in in 5..15 which is invalid
• Adding parentheses around the range
• Using three-dot range 5...15 which excludes 15

3.

What will be the output of this Ruby code?

score = 75
case score
in 0..49 then puts "Fail"
in 50..79 then puts "Pass"
in 80..100 then puts "Excellent"
else puts "Invalid"
end

medium

A. Pass

B. Fail

C. Excellent

D. Invalid

Solution

1. Step 1: Check which range includes 75

   75 is not in 0..49 but is in 50..79.

2. Step 2: Match the corresponding output

   The code prints "Pass" when score is in 50..79.

3. Final Answer:

   Pass -> Option A

4. Quick Check:

   75 in 50..79 means output "Pass" [OK]

Hint: Find which range includes the value, then pick that output [OK]

Common Mistakes:

• Choosing "Fail" because 75 is greater than 49
• Confusing inclusive and exclusive ranges
• Ignoring the order of case branches

4.

Identify the error in this Ruby code snippet using case with pattern matching:

value = 10
case value
in 1..5
  puts "Low"
in 6..10
  puts "Medium"
else
  puts "High"
end

medium

A. Missing then after in clauses

B. No error; code runs and prints "Medium"

C. Ranges should be written as arrays inside in

D. The case statement should use when instead of in

Solution

1. Step 1: Check syntax of case with in and ranges

   Using in with ranges inside case is valid Ruby syntax.

2. Step 2: Verify output for value 10

   10 matches the range 6..10, so it prints "Medium".

3. Final Answer:

   No error; code runs and prints "Medium" -> Option B

4. Quick Check:

   in with ranges works fine [OK]

Hint: Remember in works like when for pattern matching [OK]

Common Mistakes:

• Thinking then is mandatory after in
• Confusing in with when
• Trying to write ranges as arrays

5.

Given this Ruby code, what will be the output?

data = [3, 7, 12, 18]
case data
in [Integer, Integer, Integer, Integer]
  puts "All integers"
in [Integer, Integer, Integer, 18]
  puts "Last is 18"
else
  puts "No match"
end

hard

A. No match

B. Last is 18

C. All integers

D. SyntaxError

Solution

1. Step 1: Understand array pattern matching order

   The case checks patterns in order. The first pattern matches any array of four integers.

2. Step 2: Check if data matches first pattern

   Data is [3,7,12,18], all integers, so it matches the first pattern.

3. Step 3: Confirm second pattern is not reached

   Since first pattern matches, second is skipped.

4. Final Answer:

   All integers -> Option C

5. Quick Check:

   First matching pattern runs, so output is "All integers" [OK]

Hint: Patterns checked top-down; first match wins [OK]

Common Mistakes:

• Assuming second pattern runs despite first matching
• Confusing element types with values in patterns
• Expecting syntax error due to pattern complexity