Case with ranges and patterns in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a case statement used for in Ruby?

A case statement lets you check a value against multiple conditions and run code based on which condition matches. It's like choosing between many options.

beginner

How do ranges work inside a Ruby case statement?

Ranges like 1..5 represent a sequence of values. In a case, Ruby checks if the value falls inside the range to decide which code to run.

intermediate

What is pattern matching in Ruby's case statement?

Pattern matching lets you check if a value fits a certain shape or structure, like matching parts of an array or hash, and then run code based on that.

beginner

Explain this Ruby code snippet:

case age
when 0..12 then "Child"
when 13..19 then "Teen"
else "Adult"
end

This code checks the value of age. If it's between 0 and 12, it returns "Child". If between 13 and 19, it returns "Teen". Otherwise, it returns "Adult".

intermediate

How does Ruby decide which when clause matches in a case statement?

Ruby compares the case value with each when condition using the === operator. The first match runs its code, and then Ruby stops checking further.

In Ruby, what does 1..5 represent inside a case statement?

A A range including numbers 1 through 5

B An array of numbers 1 to 5

C A pattern matching any number

D A string from '1' to '5'

The 1..5 syntax creates a range including numbers 1, 2, 3, 4, and 5.

What will this Ruby code output if score = 85?

case score
when 90..100 then "Excellent"
when 75..89 then "Good"
else "Needs Improvement"
end

A "Needs Improvement"

B "Excellent"

C "Good"

D An error

85 falls in the range 75..89, so the output is "Good".

Which operator does Ruby use internally to check when conditions in a case statement?

A !=

B ==

C <=

D ===

Ruby uses the === operator to test if the case value matches a when condition.

What does pattern matching in a Ruby case statement allow you to do?

A Match exact values only

B Match values based on structure or shape

C Only match numbers

D Ignore the value completely

Pattern matching lets you check if a value fits a certain structure, like parts of an array or hash.

What will this Ruby code return?

case [1, 2, 3]
when [1, 2, 3] then "Exact match"
when [1, 2] then "Partial match"
else "No match"
end

A "Exact match"

B "Partial match"

C "No match"

D An error

The array matches exactly the first when condition, so it returns "Exact match".

Explain how Ruby's case statement works with ranges and how it decides which block to execute.

Think about how Ruby checks if a value falls inside a range.

Describe what pattern matching means in Ruby's case statement and give an example of when it might be useful.

Consider matching parts of a data structure, not just simple values.

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