while loop aggregation (class slides)

CSc 110 - while loop aggregation

while loops

• Using an index variable:
  • Defined before the loop
  • Used in the condition of the loop
  • Changed within the loop
• Using a temporary variable for aggregation:
  • Defined before the loop
  • Changed within the loop
  • Returned outside the loop

while loops with aggregation

total = 0
index = 1
while index <= 5:
    print('adding ' + str(index))
    total = total + index
    index = index + 1
    
print(total)

adding 1
adding 2
adding 3
adding 4
adding 5
15

Write a function

1. Its name is sum_all
2. It takes two numeric arguments: low and high
3. It runs a loop that iterates through the values low and high summing all values (HINT: you need to create a variable that will aggregate or accumulate the sum)
4. It returns the sum of all values between low and high
5. Use while (define an index before the loop, use index in the while condition, change the index inside the loop)

Write a function – solution

Write more test cases for this function.

def sum_all(low, high):
  total = 0
  current_number = low
  while current_number <= high:
    total += current_number
    current_number += 1
  return total
    
def main():
  print( sum_all(1, 2) ) # 3
  print( sum_all(0, 5) ) # 15
  
main()

3
15

Write a function

Write a function called count_vowels that takes a string as argument, and returns an integer with the number of vowels in the string.

HINT: use in to determine if a character is a vowel

assert count_vowels("banana") == 3
assert count_vowels("fly") == 0

Solution

def count_vowels(string):
  index = 0
  count = 0
  while index < len(string):
    if string[index] in "aeiou":
      count += 1
    index += 1
  return count

def main():
  assert count_vowels("banana") == 3
  assert count_vowels("fly") == 0
  print("End of tests.")
  
main()

End of tests.

Write a function

1. Its name is vowels_only
2. It takes a string argument
3. It builds a new string containing only the vowels in the string argument
4. It returns new string with vowels only (define an index before the loop, use index in the while condition, change index inside the loop)

print( vowels_only("banana") ) # "aaa"
print( vowels_only("fly") ) # ""

Write a function – solution

Write more test cases for this function.

def vowels_only(string):
  new_string = ""
  index = 0
  while index < len(string):
    if string[index] in "aeiou":
      new_string += string[index]
    index += 1
  return new_string

def main():
  print( vowels_only("banana") ) # "aaa"
  
main()

aaa

Write a function

1. Its name is factorial
2. It takes a numeric argument number
3. It returns the factorial of number
4. The factorial of a number is the product of itself and all the integers below it – factorial of 4 = 1 * 2 * 3 * 4 = 24
5. Use while

print( factorial(4) ) # 24
print( factorial(5) ) # 120
print( factorial(0) ) # 1

Write a function – solution

Write more test cases for this function.

def factorial(number):
  result = 1
  index = 1
  while index <= number:
    result *= index
    index += 1
  return result

def main():
  assert factorial(4) == 24
  assert factorial(5) == 120
  assert factorial(0) == 1
  
main()

Submit code for attendance

Submit your factorial function to Gradescope for attendance.

Name your file factorial.py

Write a function

1. Its name is power
2. It takes two numeric arguments: base and exp
3. It returns the base to the power of exp
4. Don’t use the ** operator, use a while loop (define an index before the loop, use index in the while condition, change index inside the loop)

assert power(2, 3) == 8
assert power(3, 3) == 27

Write a function – solution

Write more test cases for this function.

def power(base, exp):
  result = 1
  index = 1
  while index <= exp:
    result *= base
    index += 1
  return result

def main():
  print( power(2, 3) ) # 8
  print( power(3, 3) ) # 27
  
main()

8
27