How to Use Loop Do in Ruby: Simple Guide with Examples

In Ruby, loop do creates an infinite loop that repeatedly runs the code inside its block until you explicitly stop it with break. It is useful for running code continuously or until a condition is met inside the loop.

Syntax

The loop do syntax starts an infinite loop. The code inside the do...end block runs repeatedly. Use break inside the block to stop the loop when needed.

• loop do: begins the loop
• code block: the repeated code inside do...end
• break: exits the loop

ruby

loop do
  # code to repeat
  break # stops the loop
end

Example

This example prints numbers from 1 to 5 using loop do. It uses a counter variable and break to stop after 5.

ruby

count = 1
loop do
  puts count
  break if count >= 5
  count += 1
end

Output

1
2
3
4
5

Common Pitfalls

A common mistake is forgetting to use break, which causes an infinite loop that never stops. Another is placing break incorrectly so the loop never ends or ends too early.

ruby

count = 1
loop do
  puts count
  count += 1
  # Missing break causes infinite loop
end

# Correct way:
count = 1
loop do
  puts count
  break if count > 5
  count += 1
end

Quick Reference

Use loop do for infinite loops that you control with break. Remember to always include a break condition to avoid freezing your program.

Keyword	Purpose
loop do	Starts an infinite loop
break	Exits the loop
do...end	Defines the block of code to repeat

Key Takeaways

Use loop do to create an infinite loop in Ruby.

Always include a break statement inside the loop to stop it.

The code inside do...end runs repeatedly until break is called.

For counting or conditional loops, control the exit with a variable and break.

Forgetting break causes infinite loops that freeze your program.