Why error handling uses rescue in Ruby - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code using rescue?

Look at this Ruby code. What will it print when run?

Ruby

def divide(a, b)
  a / b
rescue ZeroDivisionError
  "Cannot divide by zero"
end

puts divide(10, 0)

A Cannot divide by zero

B 0

C 10

D ZeroDivisionError

💡 Hint

Think about what happens when you divide by zero in Ruby and how rescue handles it.

The code tries to divide 10 by 0, which causes a ZeroDivisionError. The rescue block catches this error and returns the string "Cannot divide by zero" instead of crashing.

🧠 Conceptual

intermediate

Why do we use rescue in Ruby error handling?

Choose the best reason why Ruby uses rescue for error handling.

A To automatically fix all errors without programmer input

B To catch and handle errors so the program can continue running

C To make the code shorter without any error handling

D To speed up the program execution

💡 Hint

Think about what happens if an error is not handled in a program.

Rescue is used to catch errors and handle them gracefully, so the program does not crash and can continue running or provide a helpful message.

🔧 Debug

advanced

What error does this Ruby code raise?

This code tries to open a file and read it. What error will it raise?

Ruby

def read_file(filename)
  File.open(filename) do |file|
    file.read
  end
rescue
  "File not found"
end

puts read_file("missing.txt")

A Errno::ENOENT

B SyntaxError

C FileNotFoundError

D NoMethodError

💡 Hint

Check Ruby's error class for missing files.

Ruby raises Errno::ENOENT when a file is missing. The rescue block catches this error and returns "File not found".

❓ Predict Output

advanced

What is the output of this nested rescue example?

What will this Ruby code print?

Ruby

def test
  begin
    raise "Oops"
  rescue RuntimeError
    begin
      raise "Inner error"
    rescue
      "Handled inner"
    end
  end
end

puts test

A RuntimeError

B Oops

C Handled inner

D Unhandled exception

💡 Hint

Look at how the inner rescue handles the second raise.

The outer begin raises "Oops" which is rescued. Inside that rescue, another error "Inner error" is raised and rescued, returning "Handled inner".

🚀 Application

expert

How many times will the rescue block run in this code?

Count how many times the rescue block executes in this Ruby code.

Ruby

count = 0
3.times do |i|
  begin
    raise "Error at #{i}" if i.even?
  rescue
    count += 1
  end
end

puts count

A 1

B 0

C 3

D 2

💡 Hint

Check which values of i are even in the loop.

The loop runs 3 times with i = 0,1,2. Errors are raised only when i is even (0 and 2), so rescue runs twice.