Numeric.times / upto / downto / step

# Repeats n times (from 0 to n-1).
n.times { |i| process }

# Counts up from start to stop, incrementing by 1 each time.
start.upto(stop) { |i| process }

# Counts down from start to stop, decrementing by 1 each time.
start.downto(stop) { |i| process }

# Counts from start to stop, incrementing by step each time.
start.step(stop, step) { |i| process }

# times: repeats a specified number of times.
3.times { |i| print "#{i} " }
puts  # 0 1 2

# You can omit the block variable if you don't need the index.
3.times { print "★ " }
puts  # ★ ★ ★

# upto: iterates in ascending order.
1.upto(5) { |i| print "#{i} " }
puts  # 1 2 3 4 5

# downto: iterates in descending order.
5.downto(1) { |i| print "#{i} " }
puts  # 5 4 3 2 1

# step: iterates with a custom step value.
1.step(10, 2) { |i| print "#{i} " }
puts  # 1 3 5 7 9

# Floating-point steps are also supported.
0.0.step(1.0, 0.25) { |f| print "#{f} " }
puts  # 0.0 0.25 0.5 0.75 1.0

# Practical example: countdown.
puts "Countdown starts!"
5.downto(1) { |i| puts "#{i}..." }
puts "Blastoff!"

In Ruby, integers themselves have iterator methods, so you can write simple loops without using for or while. This is because Ruby follows the design philosophy that "everything is an object."

times passes an index (starting from 0) into the block. If you don't need the index, you can omit the block variable. upto and downto each iterate from a start value to an end value in steps of 1.

If the start value is greater than the stop value when using upto, or if stop is greater than start with a negative step in step, the block will never execute. Make sure the intended range is correct before using these methods.

You can also loop over a range object using Range#step. For integer predicate methods, see Integer#even? / odd? / zero?.