def print_arr(arr)
  arr.each do |inner|
    puts inner.join
  end
end

def print_cross(n)
	arr = Array.new(n) { Array.new(n) { ' ' } }
	0.upto(n-1) {|i| arr[i][i] = 'X'; arr[n-1-i][i] = 'X'}
	print_arr arr
end

print_cross 9