input: Write a function to find the smallest number in a given list of integers. If the list is empty, return None.
  
  def smallestNumber(nums):
      if not nums:
          return None
      smallest = nums[0]
      for i in range(1, len(nums)):
          if nums[i] < smallest:
              smallest = nums[i]
      return smallest
  
  assert smallestNumber([4, 5, 6, 7, 8]) == 4
  assert smallestNumber([8, 3, 5, 1, 9]) == 1
  assert smallestNumber([10]) == 10
  assert smallestNumber([]) == None
  assert smallestNumber([-1, -5, -3, -2]) == -5
output: def smallestNumber(nums):
      if not nums:
          return None
      smallest = nums[0]
      for i in range(1, len(nums)):
          if nums[i] < smallest:
              smallest = nums[i]
      return smallest