a = Array.new(6)
0.upto(5){ |i|
  a[i] = i
}

b = []
0.upto(5){ |i|
  b += [i]
}

c = (0..5).to_a


[a, b, c].each do |i|
  print "#{i.class}\t#{i.length}\t#{i.inspect}\n"
end

__END__

Results:

Array 6	[0, 1, 2, 3, 4, 5]
Array	6	[0, 1, 2, 3, 4, 5]
Array	6	[0, 1, 2, 3, 4, 5]