Multiple rescue clauses in Ruby - Mini Project: Build & Apply

Handling Errors with Multiple Rescue Clauses in Ruby

📖 Scenario: Imagine you are writing a small program that divides numbers. Sometimes, the user might enter zero or a wrong input, causing errors. You want to handle these errors nicely so the program doesn't crash.

🎯 Goal: You will build a Ruby program that divides two numbers and uses multiple rescue clauses to handle different types of errors separately.

📋 What You'll Learn

Create two variables with exact values for numerator and denominator

Create a variable called result initialized to nil

Use a begin block to perform division

Add multiple rescue clauses to handle ZeroDivisionError and TypeError

Print the result or an error message

💡 Why This Matters

🌍 Real World

Handling errors gracefully is important in real programs to avoid crashes and give helpful messages to users.

💼 Career

Knowing how to use multiple rescue clauses helps you write robust Ruby code that can handle different problems clearly.

1

Set up numerator and denominator variables

Create a variable called numerator and set it to 10. Create another variable called denominator and set it to 0.

Ruby

# Create numerator and denominator variables with values 10 and 0
# Your code here

Hint

Use simple assignment like numerator = 10 and denominator = 0.

2

Initialize result variable

Create a variable called result and set it to nil.

Ruby

numerator = 10
 denominator = 0
# Initialize result variable to nil
# Your code here

Hint

Use result = nil to start with no value.

3

Add begin block with multiple rescue clauses

Write a begin block where you set result to numerator / denominator. Add two rescue clauses: one for ZeroDivisionError that sets result to the string "Cannot divide by zero", and one for TypeError that sets result to "Invalid types for division".

Ruby

numerator = 10
 denominator = 0
result = nil
# Add begin block with multiple rescue clauses
# Your code here

Hint

Use begin and rescue keywords to catch errors separately.

4

Print the result

Write puts result to display the value of result.

Ruby

numerator = 10
 denominator = 0
result = nil
begin
  result = numerator / denominator
rescue ZeroDivisionError
  result = "Cannot divide by zero"
rescue TypeError
  result = "Invalid types for division"
end
# Print the result
# Your code here

Hint

Use puts result to show the output.

Practice

1. What is the purpose of using multiple rescue clauses in Ruby?

easy

A. To repeat the same error handling multiple times

B. To run code only when no errors occur

C. To handle different types of errors with specific responses

D. To skip error handling entirely

Solution

1. Step 1: Understand rescue clauses

   Multiple rescue clauses allow you to catch different error types separately.

2. Step 2: Purpose of specific error handling

   This helps you respond differently depending on the error type.

3. Final Answer:

   To handle different types of errors with specific responses -> Option C

4. Quick Check:

   Multiple rescue clauses = specific error handling [OK]

Hint: Multiple rescue clauses catch different errors separately [OK]

Common Mistakes:

• Thinking rescue clauses run only when no errors occur
• Assuming multiple rescue repeats same handling
• Believing rescue skips error handling

2. Which of the following is the correct syntax for multiple rescue clauses in Ruby?

easy

A. try
# code
rescue ZeroDivisionError
# handle zero division
rescue StandardError
# handle other errors
end

B. begin
# code
catch ZeroDivisionError
# handle zero division
catch StandardError
# handle other errors
end

C. begin
# code
rescue ZeroDivisionError, StandardError
# handle errors
end

D. begin
# code
rescue ZeroDivisionError
# handle zero division
rescue StandardError
# handle other errors
end

Solution

1. Step 1: Identify Ruby error handling syntax

   Ruby uses begin and rescue for error handling, not try or catch.

2. Step 2: Check multiple rescue clauses

   Multiple rescue clauses are written one after another inside begin...end.

3. Final Answer:

   begin # code rescue ZeroDivisionError # handle zero division rescue StandardError # handle other errors end -> Option D

4. Quick Check:

   Ruby uses begin-rescue-end with multiple rescue [OK]

Hint: Use begin-rescue-end blocks for multiple error types [OK]

Common Mistakes:

• Using try or catch instead of rescue
• Combining errors in one rescue without comma
• Incorrect block keywords

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

begin
  1 / 0
rescue ZeroDivisionError
  puts 'Zero division error caught'
rescue StandardError
  puts 'Standard error caught'
end

medium

A. Zero division error caught

B. Standard error caught

C. No output, program crashes

D. SyntaxError

Solution

1. Step 1: Identify the error raised

   The code 1 / 0 raises a ZeroDivisionError.

2. Step 2: Match error with rescue clauses

   The first rescue clause catches ZeroDivisionError and prints the message.

3. Final Answer:

   Zero division error caught -> Option A

4. Quick Check:

   ZeroDivisionError triggers first rescue [OK]

Hint: Match error type to first rescue clause that fits [OK]

Common Mistakes:

• Assuming StandardError rescue runs first
• Thinking program crashes without rescue
• Confusing syntax error with runtime error

4. Identify the error in this Ruby code with multiple rescue clauses:

begin
  puts 'Start'
rescue
  puts 'Rescue block'
rescue ZeroDivisionError
  puts 'Zero division error'
end

medium

A. Missing ensure block causes error

B. Multiple rescue clauses after a generic rescue cause syntax error

C. No error, code runs fine

D. Rescue clauses must be inside methods only

Solution

1. Step 1: Check for syntax errors

   In Ruby, a generic rescue clause must come after all specific rescue clauses. Placing a generic rescue before specific ones causes a syntax error.

2. Step 2: Analyze the code

   The code places a generic rescue first, then a specific rescue, which is invalid syntax.

3. Final Answer:

   Multiple rescue clauses after a generic rescue cause syntax error -> Option B

4. Quick Check:

   Generic rescue must be last [OK]

Hint: Generic rescue clause must come after specific rescue clauses [OK]

Common Mistakes:

• Thinking generic rescue before specific causes syntax error
• Believing ensure block is mandatory
• Assuming rescue clauses only work inside methods

5. Given this Ruby code, what will be printed?

def test
  begin
    raise ArgumentError, 'Wrong argument'
  rescue ZeroDivisionError
    puts 'Zero division error'
  rescue ArgumentError
    puts 'Argument error caught'
  ensure
    puts 'Always runs'
  end
end
test

hard

A. Argument error caught
Always runs

B. Zero division error
Always runs

C. Always runs
Argument error caught

D. No output, error not handled

Solution

1. Step 1: Identify raised error

   The code raises ArgumentError with message 'Wrong argument'.

2. Step 2: Match rescue clauses

   The ArgumentError rescue clause runs and prints 'Argument error caught'.

3. Step 3: Understand ensure block

   The ensure block always runs, printing 'Always runs'.

4. Final Answer:

   Argument error caught Always runs -> Option A

5. Quick Check:

   ArgumentError rescued, ensure always runs [OK]

Hint: Ensure block runs after rescue regardless of error [OK]

Common Mistakes:

• Thinking ensure runs before rescue
• Assuming wrong rescue clause runs
• Ignoring ensure block output