Ruby Loops

Loops are used to execute a block of code repeatedly until a specified condition is met. This helps us avoid writing the same code again and again.

Ruby provides many looping techniques. The most common loops in Ruby are:

• while loop
• until loop
• for loop
• times loop
• each loop
• loop do...end
• begin...end while

Let's start with the while loop.

Ruby while Loop

The while loop executes a block of code as long as the given condition is true. Its syntax is:

while condition
  # Code to execute
end

Here's how this loop works:

1. The while loop first checks the condition.
2. If the condition is true, the code inside the loop is executed.
3. The loop continues until the condition becomes false.
4. The loop is never executed if the condition is false from the outset.

Example: Ruby while Loop

num = 1

# Use while loop to print numbers from 1 to 3
while num <= 3
  puts num
  num += 1
end

puts "Loop finished!"

Output

1
2
3
Loop finished!

Here, the loop runs three times because of the condition num <= 3. Here's how the program works:

1. The num variable is initialized to 1.
2. The while loop starts because the condition num <= 3 is true (since 1 is less than 3).
3. Inside the loop, the value of num is printed. Thus, we get 1 as an output.
4. Then, the value of num is increased by 1 with the code num += 1.
5. Thus, the first iteration of the loop is over.
6. The second iteration begins because num <= 3 is true again (since 2 is less than 3).
7. The whole process repeats itself until num is greater than 3. Then, the loop terminates.
8. As a result, all numbers from 1 to 3 are printed.
9. Finally, the code outside of the loop is executed. Thus, Loop finished! is printed.

To learn more, visit Ruby while Loop.

Ruby until Loop

The until loop is the opposite of the while loop. It runs a block of code until the given condition becomes true. Its syntax is:

until condition
  # Code to execute
end

Example: Ruby until Loop

x = 1

until x > 3
  puts x
  x += 1
end

Output

1
2
3

In this example, the loop runs until x > 3 becomes true. In other words, it stops when x becomes 4.

Ruby for Loop

The for loop in Ruby is used to iterate over a range or a collection (like arrays or hashes). Its syntax is:

for variable in collection
  # Code to execute
end

Here,

• collection - A range of values, or a collection of values like arrays or hashes.
• variable - A placeholder that takes the value of each element in the collection during each iteration.

Note: Many Ruby programmers prefer the each loop over the for loop when iterating over collections.

Example: Ruby for Loop with Range

for i in 4..6
  puts i
end

Output

4
5
6

Here, the for loop iterates over the range 4..6. As a result, the loop runs three times over the numbers 4, 5, and 6.

In each iteration of the loop, the variable i takes values from 4 to 6, which is then printed to the screen. Here's how it works:

Example: Ruby for Loop with Array

people = ["Bob", "Alex", "Sharon", "Cassie"]

for person in people
  puts person
end

Output

Bob
Alex
Sharon
Cassie

Here, the for loop iterates over the people array. In each iteration of the loop, the variable person takes the corresponding element of the array. Here's how this works:

To learn more, visit Ruby for and each Loops.

Ruby times Loop

The times loop is a concise way to repeat something a fixed number of times.

The syntax of the times loop is:

n.times do
  # Code to execute
end

Here, the loop is repeated n number of times.

Example: Ruby times Loop

3.times do
  puts "Knock!"
end

Output

Knock!
Knock!
Knock!

The above loop runs three times. In each iteration, we print the string "Knock!". So, Knock! is printed three times.

Note: We often use the times loop for simple repetitions.

Ruby each Loop

The each loop is used to iterate over each element in a collection like an array. Its syntax is:

collection.each do |item|
  # Code using item
end

Here,

• collection - A collection of values like arrays or hashes.
• item - A placeholder that takes the value of each element in the collection during each iteration.

Example: Ruby each Loop

people = ["Bob", "Alex", "Sharon", "Cassie"]

people.each do |person|
  puts person
end

Output

Bob
Alex
Sharon
Cassie

Here, the each loop runs once for each item in the people array.

In each iteration of the loop, the person variable takes a single element from the people array, which is similar to how our for loop example works:

To learn more, visit Ruby for and each Loops.

Ruby loop do...end

The loop do...end runs infinitely unless we explicitly use a control statement like break to exit the loop. Its syntax is:

loop do
  # Code to execute
end

Example: Ruby loop with break

i = 1

loop do
  puts i
  i += 1
    
  # Terminate the loop if i is greater than 3
  break if i > 3
end

Output

1
2
3

Here, the loop runs infinitely, but the break statement stops it when i becomes greater than 3.

Notice that this loop behaves similarly to a while loop, but we need to manage the break condition ourselves.

To learn more, visit Ruby loop do.

Ruby begin...end while Loop

Ruby also provides the begin...end while loop, which is similar to a do...while loop in other languages.

In this loop, the code is executed at least once before the condition is checked. Its syntax is:

begin
  # Code to execute
end while condition

Here, the begin loop first executes the code, and only then checks the condition:

• If the condition is true, the loop runs again.
• If the condition is false, the loop ends.

Example: Ruby begin...end while Loop

x = 1

begin
  puts x
  x += 1
end while x <= 3

Output

1
2
3

Here, the loop prints the value of x starting from 1 and runs until x becomes 4.

As you can see, this loop acts just like a while loop, but the first iteration always happens regardless of whether the condition is true or false.

Note: The begin...end while loop is discouraged by many Ruby developers because it can reduce readability and make code harder to maintain. Instead, they prefer loop do...end with a break statement, which is clearer and more flexible.