while loop aggregation (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

Adding numbers from 1 to 5:

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

while loops table

Start with total = 0, index = 1:

index <= 5	total = total + index	index = index + 1
True	total = 0 + 1	index = 1 + 1
True	total = 1 + 2	index = 2 + 1
True	total = 3 + 3	index = 3 + 1
True	total = 6 + 4	index = 4 + 1
True	total = 10 + 5	index = 5 + 1
False	-	-

Write a function

Its name is sum_all and takes two numeric arguments: low and high. It runs a loop that iterates through the values low and high summing all values. It returns the sum of all values between low and high.

HINT: Create a variable that will aggregate the sum. Use while (set the index as the low before the loop, use index in the while condition, update the index inside the loop).

assert sum_all(1, 3) == 6
assert sum_all(0, 5) == 15

Write a function – solution

def sum_all(low, high):
  total = 0
  index = low
  while index <= high:
    total += index
    index += 1
  return total
    
def main():
  assert sum_all(1, 3) == 6
  assert sum_all(0, 5) == 15
  
main()

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. The vowels are "a","e","i","o", and "u".

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

Write a function – 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

Its name is factorial and takes a numeric argument number. It returns the factorial of number. The factorial of a number is the product of that number and every number that comes before it, down to one.

For example, factorial of 4: 1 * 2 * 3 * 4 = 24.

Name your file factorial.py and submit to Gradescope.

assert factorial(4) == 24
assert factorial(5) == 120
assert factorial(0) == 1

Write a function – solution

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()

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, 4) == 16
assert power(3, 2) == 9

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():
  assert power(2, 4) == 16
  assert power(3, 2) == 9
    
main()

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

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