Finished int_under_100_to_str(number)

numberwords.py

@@ -15,13 +15,20 @@ TENS_NAMES = [
 ]
 
 def int_under_1000000_to_str(number):
+    pass
 
         
 def int_under_1000_to_str(number):
+    pass
 
 
 def int_under_100_to_str(number):
-
+    check_number_in_range(number, 0, 100)
+    if number < 10:
+        return int_under_10_to_str(number)
+    if number < 20:
+        return TWEEN_AND_TEEN_NAMES[number % 10]
+    return TENS_NAMES[number // 10 - 1] + "-" + DIGIT_NAMES[number % 10]
 
 def int_under_10_to_str(number):
     check_number_in_range(number, 0, 10)
@@ -32,9 +39,9 @@ def check_number_in_range(number, minimum, maximum):
     Raises an error if the number is not in range.
     """
     if number < minimum:
-        raise ValueError(f"{number} must not be below {minimum}.")
+        raise ValueError("{number} must not be below {minimum}.")
     if number >= maximum:
-        raise ValueError(f"{number} must be less than {maximum}.")
+        raise ValueError("{number} must be less than {maximum}.")
 
 def divide_with_remainder(dividend, divisor):
     """Divides one number by another, using whole-number division. 
@@ -43,4 +50,4 @@ def divide_with_remainder(dividend, divisor):
     """
     quotient = dividend // divisor
     remainder = dividend % divisor
-    return quotient, remainder
+    return quotient, remainder