Ruby while Loop

Execute code while a condition is true

⏰ What is a while Loop?

The while loop executes code repeatedly as long as a condition remains true. It checks the condition before each iteration, making it perfect for unknown repetition counts. 


# Basic while loop
count = 1
while count <= 3
  puts "Count: #{count}"
  count += 1
end

Output: 

Count: 1
Count: 2
Count: 3

while Loop Syntax

📝

Basic Syntax

Standard while loop structure 

while condition
  # code block
end
🔍

Condition Check

Evaluated before each iteration 

x = 0
while x < 5
  puts x
  x += 1
end
➕

Increment

Update variable to avoid infinite loop 

i = 1
while i <= 3
  puts i
  i += 1  # Important!
end
⚡

One-line Form

Compact syntax for simple loops 

i = 0
puts i += 1 while i < 3

🔹 Basic while Loop

The while loop continues executing as long as the condition evaluates to true. Always remember to update the condition variable to prevent infinite loops. 

# Print numbers 1 to 5
number = 1
while number <= 5
  puts "Number: #{number}"
  number += 1
end

puts "Loop finished!"

Output: 

Number: 1
Number: 2
Number: 3
Number: 4
Number: 5
Loop finished!

🔹 while Loop with Conditions

You can use various conditions in while loops, including comparisons, boolean values, and method calls that return true or false. 

# Loop with comparison
temperature = 15
while temperature < 20
  puts "Temperature: #{temperature}°C - Too cold!"
  temperature += 2
end
puts "Temperature: #{temperature}°C - Perfect!"

# Loop with boolean
running = true
count = 0
while running
  count += 1
  puts "Running... #{count}"
  running = false if count >= 3
end

Output: 

Temperature: 15°C - Too cold!
Temperature: 17°C - Too cold!
Temperature: 19°C - Too cold!
Temperature: 21°C - Perfect!
Running... 1
Running... 2
Running... 3

🔹 Nested while Loops

You can place one while loop inside another to create nested loops. This is useful for working with multi-dimensional data or creating patterns. 

# Multiplication table
i = 1
while i <= 3
  j = 1
  while j <= 3
    print "#{i}x#{j}=#{i*j} "
    j += 1
  end
  puts  # New line
  i += 1
end

Output: 

1x1=1 1x2=2 1x3=3 
2x1=2 2x2=4 2x3=6 
3x1=3 3x2=6 3x3=9

🔹 Common while Loop Patterns

Here are some frequently used patterns with while loops that you'll encounter in real programming: 

# Countdown
countdown = 5
while countdown > 0
  puts countdown
  countdown -= 1
end
puts "Go!"

# Sum calculation
sum = 0
num = 1
while num <= 5
  sum += num
  num += 1
end
puts "Sum of 1 to 5: #{sum}"

# User input simulation (with counter)
attempts = 0
max_attempts = 3
while attempts < max_attempts
  puts "Attempt #{attempts + 1}"
  attempts += 1
end

Output: 

5
4
3
2
1
Go!
Sum of 1 to 5: 15
Attempt 1
Attempt 2
Attempt 3

🔹 while Loop Best Practices

Follow these guidelines to write effective and safe while loops:

Important Tips:

  • Always update the condition: Make sure the loop variable changes to avoid infinite loops
  • Initialize before the loop: Set your counter or condition variable before the while statement
  • Keep conditions simple: Complex conditions make code harder to understand
  • Use meaningful variable names: Use names like 'count' or 'index' instead of 'i' or 'x'
  • Consider alternatives: Sometimes .times or .each methods are clearer than while loops 
# Good practice
counter = 0
while counter < 5
  puts "Iteration #{counter}"
  counter += 1  # Don't forget this!
end

# Avoid infinite loops!
# BAD: This will run forever
# x = 0
# while x < 5
#   puts x
#   # Missing: x += 1
# end

🧠 Test Your Knowledge

What happens if you forget to update the loop variable in a while loop?