Update factorial_iterative.py

Address review: add doctests and descriptive parameter name

Author: agarwalpranay02

maths/factorial_iterative.py

@@ -1,16 +1,24 @@
-def factorial_iterative(n: int) -> int:
+def factorial_iterative(number: int) -> int:
     """
-    Return the factorial of n using an iterative approach.
-    Raises ValueError for negative inputs.
+    Return the factorial of a non-negative integer using an iterative method.
+
+    >>> factorial_iterative(5)
+    120
+    >>> factorial_iterative(0)
+    1
+    >>> factorial_iterative(1)
+    1
     """
-    if n < 0:
+    if number < 0:
         raise ValueError("Input must be a non-negative integer")
+
     result = 1
-    for i in range(1, n + 1):
+    for i in range(2, number + 1):
         result *= i
     return result
 
 
 if __name__ == "__main__":
     # simple demonstration
     print(factorial_iterative(5))  # expected 120
+