input: Write a function to find the smallest number in a given list. 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([9, 2, 5, 3, 8])==2
  assert smallestNumber([1, 2, 3, 4, 5])==1
  assert smallestNumber([5])==5
  assert smallestNumber([])==None
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