Loops in Ruby language

Loops are a way to execute sequence of statements many times in Ruby when some of the condition evaluates to true or false.

Ruby supports varieties of looping statements.

• loop method
• while Statement
• do-while Statement
• until Statement
• for Statement
• redo Statement
• retry Statement

loop method

By using Kernel#loop, we can create the looping over Ruby statements.

loop do
  puts "Hello Loop (Ctrl + c to stop me)"
end

Conditional loop

In the above example, you can see we have created an infinite loop and we need to press Ctrl + C to stop it.

However, we can use the break keyword to exit the loop. But, if we add a conditional statement than it becomes a Conditional Loop.

# Print Hello only 5 fines
count = 1
loop do
  puts "#{count} Hello"
  if count == 5
    break
  end

  count += 1
end

puts "Printing Hello ends"

Output:

1 Hello
2 Hello
3 Hello
4 Hello
5 Hello
Printing Hello ends

NOTE: We can use the next keyword to skip the rest of the statement and start execution from the next iteration.

while Statement

A while statement executes the code block while the condition is true.

Syntax

while conditional do # the do is optional
   code
end

Example

count = 1
while count <= 5 do
  puts "#{count} Hello"

  count += 1
end

Output:

1 Hello
2 Hello
3 Hello
4 Hello
5 Hello

do-while Statement

In this loop, the code block execute first and then the condition is checked. The loop continues till the condition is true.

Syntax

code while condition

or

begin
  code
end while condition

Example

count = 1
begin
  puts "#{count} Hello"
  if count == 5
    break
  end

  count += 1
end while count >= 5   # making condition false in first attempt

# output
1 Hello

until Statement

The until statement executes the code block until the condition is true.

Syntax

until conditional do # the do is optional
   code
end

Example

count = 1
until count > 5 do  # only difference with 'while' loop statement
  puts "#{count} Hello"

  count += 1
end

Output:

1 Hello
2 Hello
3 Hello
4 Hello
5 Hello

NOTE: Similar to do-while statement, we can have the code block executed first and condition checked after.

for Statement

The for loop executes a code block once for each element in the expression. It is used to loop over a collection of elements.

Syntax

for element in collection do # The `do` is optional here
  code
end

Example

for element in [1, 2, 3, 4, 5]
  puts "#{element} Hello"
end

Output:

1 Hello
2 Hello
3 Hello
4 Hello
5 Hello

redo Statement

The redo keyword restarts the iteration of the most internal loop, without checking loop condition.

for i in (0..5)
   if i < 3
      puts "#{i} Hello"
      i += 1
      redo
      puts "This will not evaluate"
   end
end

Output

0 Hello
1 Hello
2 Hello
1 Hello
2 Hello
2 Hello

retry Statement

The retry keyword restarts the execution of code block. It can also be used in begin-rescue statements.

count = 1
for i in (1..5)
  puts "Execution begin now"
  begin
    puts "#{i} Hello. Count #{count}"
    raise if i > 2 && count < 3
  rescue
   count += 1
   retry
  end
end

Output:

# output
Execution begin now
1 Hello. Count 1
Execution begin now
2 Hello. Count 1
Execution begin now
3 Hello. Count 1
3 Hello. Count 2
3 Hello. Count 3
Execution begin now
4 Hello. Count 3
Execution begin now
5 Hello. Count 3