input: Write a python function to find the largest number in a list of integers.
  assert find_largest_number([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]) == 10
  assert find_largest_number([10, 20, 45, 67, 84, 93]) == 93
  assert find_largest_number([5, 7, 9, 8, 6, 4, 3]) == 9
output: def find_largest_number(lst):
      if not lst:
          return None
      largest = lst[0]
      for num in lst[1:]:
          if num > largest:
              largest = num
      return largest