Ruby while Keyword

last modified April 27, 2025

This tutorial explains how to use Ruby's while keyword for creating loops. The while loop executes code repeatedly while a condition is true.

The while keyword creates a loop that runs as long as its condition evaluates to true. It checks the condition before each iteration. When the condition becomes false, the loop terminates.

while loops are fundamental for repetitive tasks in Ruby. They provide precise control over iteration when the number of repetitions isn't known beforehand.

Basic while Loop

This example demonstrates the simplest form of a while loop. The loop continues while the condition remains true.

count = 0
while count < 5
 puts "Count is #{count}"
 count += 1
end
puts "Loop finished"

The loop runs while count is less than 5. Each iteration prints the current count and increments it. The loop exits when count reaches 5.

while with User Input

This example uses while to repeatedly prompt for user input until a specific condition is met.

answer = ""
while answer.downcase != "quit"
 print "Enter a command (or 'quit' to exit): "
 answer = gets.chomp
 puts "You entered: #{answer}"
end
puts "Goodbye!"

The loop continues until the user enters "quit". The condition checks the input in a case-insensitive way. Each iteration processes the user's input.

Infinite while Loop with break

This example shows how to create an infinite loop with while true and use break to exit based on a condition.

counter = 0
while true
 puts "Counter: #{counter}"
 counter += 1
 
 break if counter >= 10
end
puts "Loop exited"

The loop runs indefinitely until the break condition is met. This pattern is useful when the exit condition is complex or appears mid-loop.

while with next Keyword

This example demonstrates using next to skip certain iterations within a while loop.

num = 0
while num < 10
 num += 1
 next if num.even?
 
 puts "Odd number: #{num}"
end
puts "Done"

The loop skips even numbers using next. Only odd numbers are printed. The loop continues until all numbers up to 10 are processed.

while Modifier Form

Ruby offers a postfix while modifier that executes code while a condition is true. This concise form is useful for single-statement loops.

count = 0
puts count += 1 while count < 5
puts "Final count: #{count}"

The postfix while executes the preceding statement repeatedly. The loop stops when the condition becomes false. This form is compact but less flexible.

Nested while Loops

This example demonstrates nested while loops to create more complex iteration patterns.

outer = 1
while outer <= 3
 inner = 1
 
 while inner <= outer
 print "#{outer}:#{inner} "
 inner += 1
 end
 
 puts
 outer += 1
end

The outer loop runs three times. The inner loop's iterations increase with each outer iteration. This creates a triangular number pattern.

while with Arrays

This example shows how to use while to process array elements without using iterator methods.

fruits = ["apple", "banana", "cherry", "date"]
index = 0
while index < fruits.length
 puts "Fruit ##{index + 1}: #{fruits[index].capitalize}"
 index += 1
end
puts "All fruits processed"

The loop processes each array element by index. It continues until all elements are visited. This approach gives manual control over array traversal.

Source

Ruby Keywords Documentation

This tutorial covered Ruby's while loops with practical examples showing basic usage, control flow, and common patterns.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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