Loop method for infinite loops in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the loop method do in Ruby?

The loop method runs the block of code inside it repeatedly forever, creating an infinite loop unless stopped with a break.

beginner

How do you stop a loop in Ruby?

You stop a loop by using the break keyword inside the block when a certain condition is met.

beginner

Example: What will this code do?

loop do
  puts "Hello"
  break
end

It will print "Hello" once and then stop because break ends the loop immediately.

intermediate

Why use loop instead of while true for infinite loops?

loop is a Ruby method designed for infinite loops and can be more readable and expressive. It also uses a block which can be clearer to write and understand.

beginner

What happens if you forget to use break inside a loop?

The program will keep running the loop forever, which can freeze or crash your program if not handled properly.

What keyword stops a loop in Ruby?

A break

B stop

C exit

D end

The break keyword immediately exits the loop.

What does this code print?

loop do
  puts "Hi"
  break
end

A Prints "Hi" forever

B Prints "Hi" once

C Prints nothing

D Causes an error

The loop prints "Hi" once and then breaks out of the loop.

Which of these is a correct way to create an infinite loop in Ruby?

A if true then ... end

B for i in 1..10 do ... end

C loop do ... end

D while false do ... end

loop do ... end runs forever unless broken.

What will happen if you run loop do puts 'Hello' end without a break?

A Prints 'Hello' once

B Throws an error

C Does not print anything

D Prints 'Hello' forever

Without break, the loop runs forever printing 'Hello'.

Why might you prefer loop do over while true?

A <code>loop</code> is more readable and idiomatic in Ruby

B <code>while true</code> is faster

C <code>loop</code> cannot be broken

D There is no difference

loop is a Ruby method designed for infinite loops and is often clearer.

Explain how the loop method works in Ruby and how you can stop it.

Think about what happens inside the block and how to exit.

Describe a situation where using loop do ... end is helpful and how to avoid problems with infinite loops.

Consider real-life tasks that repeat until a condition is met.

Practice

1. What does the Ruby code loop do; puts "Hello"; break; end do?

easy

A. Prints "Hello" once and stops the loop

B. Prints "Hello" infinitely without stopping

C. Causes a syntax error

D. Prints nothing

Solution

1. Step 1: Understand the loop structure

   The loop do ... end creates an infinite loop that repeats the code inside.

2. Step 2: Analyze the break statement

   The break immediately stops the loop after printing "Hello" once.

3. Final Answer:

   Prints "Hello" once and stops the loop -> Option A

4. Quick Check:

   loop with break stops after one iteration [OK]

Hint: Remember: break stops the infinite loop immediately [OK]

Common Mistakes:

• Thinking loop runs forever even with break
• Confusing loop with while
• Ignoring the break statement

2. Which of the following is the correct syntax to create an infinite loop using the loop method in Ruby?

easy

A. loop: do puts "Hi" end

B. loop { puts "Hi" do end }

C. loop puts "Hi" do end

D. loop { puts "Hi" }

Solution

1. Step 1: Review Ruby loop syntax

   The loop method can take a block with curly braces or do...end.

2. Step 2: Identify correct syntax

   loop { puts "Hi" } uses loop { puts "Hi" }, which is valid Ruby syntax for an infinite loop.

3. Final Answer:

   loop { puts "Hi" } -> Option D

4. Quick Check:

   loop with block braces is valid syntax [OK]

Hint: Use loop with { } or do...end for blocks [OK]

Common Mistakes:

• Placing do after loop without block
• Using colon incorrectly
• Missing block braces or do...end

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

count = 0
loop do
  puts count
  count += 1
  break if count == 3
end

medium

A. 0 1 2 3

B. 0 1 2

C. 1 2 3

D. Infinite loop printing numbers

Solution

1. Step 1: Trace the loop iterations

   Initially, count = 0. The loop prints count, then increments it by 1.

2. Step 2: Check break condition

   Loop breaks when count == 3, so it stops after printing 0, 1, and 2.

3. Final Answer:

   0 1 2 -> Option B

4. Quick Check:

   Loop stops before printing 3 due to break condition [OK]

Hint: Break stops loop before count reaches 3 [OK]

Common Mistakes:

• Including 3 in output
• Forgetting to increment count
• Assuming infinite loop

4. Identify the error in the following Ruby code using loop do:

loop do
  puts "Start"
  break
  puts "End"
end

medium

A. The code after break will never execute

B. The break statement is unreachable

C. Syntax error due to missing end

D. Infinite loop without break

Solution

1. Step 1: Understand break behavior

   The break stops the loop immediately when reached.

2. Step 2: Analyze code after break

   The puts "End" after break will never run because break exits the loop first.

3. Final Answer:

   The code after break will never execute -> Option A

4. Quick Check:

   Code after break is skipped [OK]

Hint: Code after break inside loop is ignored [OK]

Common Mistakes:

• Thinking code after break runs
• Confusing break with next
• Assuming syntax error

5. How can you use the Ruby loop do method to repeatedly ask a user for input until they type "exit"?

hard

A. Use loop without break and rely on user to close program

B. Use while loop with condition input != "exit"

C. Use loop with gets and break if input equals "exit"

D. Use for loop iterating over input strings

Solution

1. Step 1: Use loop to repeat input request

   The loop do method runs code repeatedly until broken.

2. Step 2: Use break with condition on user input

   Inside the loop, get user input with gets.chomp and break if input is "exit".

3. Final Answer:

   Use loop with gets and break if input equals "exit" -> Option C

4. Quick Check:

   loop + break on condition = controlled infinite loop [OK]

Hint: Break loop when input matches exit string [OK]

Common Mistakes:

• Not using break to stop loop
• Using wrong loop type
• Forgetting to remove newline from input