input: Write a function to calculate the product of all odd numbers in an array.
  assert product_of_odds([3, 4, 5, 6, 7]) == 105
  assert product_of_odds([1, 2, 3, 4, 5]) == 15
  assert product_of_odds([2, 4, 6, 8, 10]) == 1
output: def product_of_odds(arr):
      product = 1
      for num in arr:
          if num % 2 != 0:
              product *= num
      return product