Case/when statement in Ruby

Introduction

The case/when statement helps you choose what to do based on different conditions. It makes your code cleaner and easier to read when you have many choices.

When you want to perform different actions depending on a value, like days of the week.

When you have multiple options and want to avoid many if/else statements.

When you want to check a variable against several possible values.

When you want to make your code easier to understand by grouping conditions clearly.

Syntax

Ruby

case variable
when value1
  # code to run if variable === value1
when value2
  # code to run if variable === value2
else
  # code to run if no match
end

The case keyword starts the statement, and when checks each possible value.

The else part is optional and runs if no when matches.

Examples

This checks the value of day and prints a message based on it.

Ruby

case day
when "Monday"
  puts "Start of the week"
when "Friday"
  puts "Almost weekend"
else
  puts "Just another day"
end

You can check multiple values or ranges in one when line.

Ruby

case number
when 1, 2, 3
  puts "Small number"
when 4..6
  puts "Medium number"
else
  puts "Other number"
end

Sample Program

This program asks the user to enter a fruit name and then tells them which fruit they chose using a case/when statement.

Ruby

puts "Enter a fruit name:"
fruit = gets.chomp
case fruit.downcase
when "apple"
  puts "You chose apple."
when "banana"
  puts "You chose banana."
when "orange"
  puts "You chose orange."
else
  puts "Unknown fruit."
end

Important Notes

The case statement compares using === operator, so it works well with ranges and classes.

Remember to use end to close the case statement.

Summary

The case/when statement helps you pick actions based on a value.

It is cleaner than many if/else statements when checking many options.

You can check multiple values or ranges in one when line.

Practice

1.

What does the case/when statement do in Ruby?

easy

A. It chooses which code to run based on matching a value.

B. It repeats code multiple times.

C. It defines a new method.

D. It creates a new variable.

Solution

1. Step 1: Understand the purpose of case/when

   The case/when statement compares a value to different options to decide which code to run.

2. Step 2: Compare with other options

   Repeating code is done by loops, defining methods uses def, and variables are created by assignment, so these are incorrect.

3. Final Answer:

   It chooses which code to run based on matching a value. -> Option A

4. Quick Check:

   case/when selects code by value match [OK]

Hint: Remember: case/when picks code by matching values [OK]

Common Mistakes:

• Confusing case/when with loops
• Thinking case/when defines methods
• Believing case/when creates variables

2.

Which of the following is the correct syntax for a case/when statement in Ruby?

case x
  when 1
    puts "One"
  when 2
    puts "Two"
  else
    puts "Other"
end

easy

A. case x
when 1
puts "One"
when 2
puts "Two"
else
puts "Other"
end

B. case x {
when 1:
puts "One"
when 2:
puts "Two"
else:
puts "Other"
}

C. switch(x) {
case 1:
puts "One"
case 2:
puts "Two"
default:
puts "Other"
}

D. if x == 1 then puts "One" elsif x == 2 then puts "Two" else puts "Other" end

Solution

1. Step 1: Check Ruby case/when syntax

   Ruby uses case followed by when clauses and ends with end. No braces or colons are used.

2. Step 2: Compare options

   case x when 1 puts "One" when 2 puts "Two" else puts "Other" end matches Ruby syntax exactly. Options B and C use braces and colons like other languages. if x == 1 then puts "One" elsif x == 2 then puts "Two" else puts "Other" end is an if/elsif, not case/when.

3. Final Answer:

   case x when 1 puts "One" when 2 puts "Two" else puts "Other" end -> Option A

4. Quick Check:

   Ruby case/when uses no braces or colons [OK]

Hint: Ruby case/when uses no braces or colons, just end [OK]

Common Mistakes:

• Using braces or colons like other languages
• Confusing case/when with switch/case from other languages
• Using if/elsif instead of case/when

3.

What is the output of this Ruby code?

grade = 'B'
case grade
when 'A'
  puts "Excellent"
when 'B', 'C'
  puts "Good"
when 'D'
  puts "Pass"
else
  puts "Fail"
end

medium

A. Fail

B. Excellent

C. Pass

D. Good

Solution

1. Step 1: Identify the value of grade

   The variable grade is set to 'B'.

2. Step 2: Match grade in case/when

   The when 'B', 'C' line matches 'B', so it runs puts "Good".

3. Final Answer:

   Good -> Option D

4. Quick Check:

   grade 'B' matches when 'B', 'C' [OK]

Hint: Check all values in when line, including multiple matches [OK]

Common Mistakes:

• Only checking first value in when list
• Confusing else output
• Ignoring multiple values in one when

4.

Find the error in this Ruby code snippet:

score = 85
case score
when 90..100
  puts "A"
when 80..89
  puts "B"
when 70..79
  puts "C"
else
  puts "F"
end

Why does it not print "B" for score 85?

medium

A. Ranges in when must be strings, not numbers.

B. The case statement compares score with ranges incorrectly; use case with when and ===.

C. The code is correct; it will print "B" as expected.

D. The ranges overlap and cause confusion.

Solution

1. Step 1: Understand how case/when works with ranges

   Ruby's case/when uses the === operator, which works with ranges to check if a value is inside.

2. Step 2: Check the given score and ranges

   Score 85 falls inside 80..89, so puts "B" will run correctly.

3. Final Answer:

   The code is correct; it will print "B" as expected. -> Option C

4. Quick Check:

   Ranges work with case/when using === [OK]

Hint: Ranges work naturally in when clauses with case [OK]

Common Mistakes:

• Thinking ranges must be strings
• Believing case/when can't handle ranges
• Assuming overlapping ranges cause errors here

5.

You want to write a Ruby case/when statement that prints "Weekend" for Saturday and Sunday, "Weekday" for Monday to Friday, and "Invalid" for any other input. Which code correctly does this?

hard

A. case day
when 'Saturday', 'Sunday'
puts "Weekend"
when 'Monday'..'Friday'
puts "Weekday"
else
puts "Invalid"
end

B. case day
when 'Saturday', 'Sunday'
puts "Weekend"
when 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday'
puts "Weekday"
else
puts "Invalid"
end

C. case day
when 'Saturday'..'Sunday'
puts "Weekend"
when 'Monday'..'Friday'
puts "Weekday"
else
puts "Invalid"
end

D. case day
when ['Saturday', 'Sunday']
puts "Weekend"
when ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
puts "Weekday"
else
puts "Invalid"
end

Solution

1. Step 1: Understand how to list multiple values in when

   Use commas to separate multiple values in one when line, like when 'Saturday', 'Sunday'.

2. Step 2: Check each option

   case day when 'Saturday', 'Sunday' puts "Weekend" when 'Monday'..'Friday' puts "Weekday" else puts "Invalid" end incorrectly uses a range of strings 'Monday'..'Friday' which does not work as expected for days. case day when ['Saturday', 'Sunday'] puts "Weekend" when ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday'] puts "Weekday" else puts "Invalid" end uses arrays in when, which does not match values correctly. case day when 'Saturday'..'Sunday' puts "Weekend" when 'Monday'..'Friday' puts "Weekday" else puts "Invalid" end uses string ranges like 'Saturday'..'Sunday' which is not meaningful for days. case day when 'Saturday', 'Sunday' puts "Weekend" when 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday' puts "Weekday" else puts "Invalid" end correctly lists each weekday separately with commas.

3. Final Answer:

   case day when 'Saturday', 'Sunday' puts "Weekend" when 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday' puts "Weekday" else puts "Invalid" end -> Option B

4. Quick Check:

   Use commas for multiple values in when [OK]

Hint: Use commas, not ranges or arrays, for multiple when values [OK]

Common Mistakes:

• Using ranges of strings for days
• Using arrays inside when clauses
• Trying to use string ranges that don't work