input: Write a python function to calculate the sum of integers from 0 to a given number using a while loop.
  assert sum_integers_while(10) == 45
  assert sum_integers_while(100) == 4950
  assert sum_integers_while(1000) == 499500
output: def sum_integers_while(n):
      total = 0
      i = 0
      while i < n:
          total += i
          i += 1
      return total