CS61A Lab 1

Lab 1: Variables & Functions, Control lab01.zip

What Would Python Display? (WWPD)

Q1: WWPD: Control

Use Ok to test your knowledge with the following “What Would Python Display?” questions:

python3 ok -q control -u

Hint: Make sure your while loop conditions eventually evaluate to a false value, or they’ll never stop! Typing Ctrl-C will stop infinite loops in the interpreter.

>>> def xk(c, d):
...     if c == 4:
...         return 6
...     elif d >= 4:
...         return 6 + 7 + c
...     else:
...         return 25
>>> xk(10, 10)

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>>> xk(10, 6)

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>>> xk(4, 6)

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>>> xk(0, 0)

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>>> def how_big(x):
...     if x > 10:
...         print('huge')
...     elif x > 5:
...         return 'big'
...     elif x > 0:
...         print('small')
...     else:
...         print("nothing")
>>> how_big(7)

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>>> how_big(12)

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>>> how_big(1)

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>>> how_big(-1)

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>>> n = 3
>>> while n >= 0:
...     n -= 1
...     print(n)

______

Hint: Make sure your while loop conditions eventually evaluate to a false value, or they’ll never stop! Typing Ctrl-C will stop infinite loops in the interpreter.

>>> positive = 28
>>> while positive:
...    print("positive?")
...    positive -= 3

______
>>> positive = -9
>>> negative = -12
>>> while negative:
...    if positive:
...        print(negative)
...    positive += 3
...    negative += 3

______

Q2: WWPD: Veritasiness

Use Ok to test your knowledge with the following “What Would Python Display?” questions:

python3 ok -q short-circuit -u✂️

>>> True and 13

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>>> False or 0

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>>> not 10

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>>> not None

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>>> True and 1 / 0 and False

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>>> True or 1 / 0 or False

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>>> True and 0

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>>> False or 1

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>>> 1 and 3 and 6 and 10 and 15

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>>> -1 and 1 > 0

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>>> 0 or False or 2 or 1 / 0

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>>> not 0

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>>> (1 + 1) and 1

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>>> 1/0 or True

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>>> (True or False) and False

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Q3: Debugging Quiz

The following is a quick quiz on different debugging techniques that will be helpful for you to use in this class. You can refer to the debugging article to answer the questions.

Use Ok to test your understanding:

python3 ok -q debugging-quiz -u✂️

Parsons Problems

To work on these problems, open the Parsons editor:

python3 parsons

Q4: Add in Range

Complete add_in_range, which returns the sum of all integers between start and stop (inclusive).

def add_in_range(start, stop):
    """
    >>> add_in_range(3, 5)  # .Case 1
    12
    >>> add_in_range(1, 10)  # .Case 2
    55
    """
    "*** YOUR CODE HERE ***"
    total = 0
    while start <= stop:
        total += start
        start += 1
    return total

Q5: Digit Position Match

A number has a digit-position match if the ith-to-last digit is i. For example, 980 has the 0th-to-last digit as 0. Or 98276 has the 2nd-to-last digit as a 2.

Write a function that determine if a number n has a digit-position match at a kth-to-last digit k.

def digit_pos_match(n, k):
    """
    >>> digit_pos_match(980, 0) # .Case 1
    True
    >>> digit_pos_match(980, 2) # .Case 2
    False
    >>> digit_pos_match(98276, 2) # .Case 3
    True
    >>> digit_pos_match(98276, 3) # .Case 4
    False
    """
    "*** YOUR CODE HERE ***"
    index = 0
    while index < k:
        index = index + 1
        n = n // 105
    return n % 10 == k

Code Writing Questions

Q6: Falling Factorial

Let’s write a function falling, which is a “falling” factorial that takes two arguments, n and k, and returns the product of k consecutive numbers, starting from n and working downwards. When k is 0, the function should return 1.

def falling(n, k):
    """Compute the falling factorial of n to depth k.

    >>> falling(6, 3)  # 6 * 5 * 4
    120
    >>> falling(4, 3)  # 4 * 3 * 2
    24
    >>> falling(4, 1)  # 4
    4
    >>> falling(4, 0)
    1
    """
    "*** YOUR CODE HERE ***"
    res = 1
    while k:
        res = res * n
        n = n - 1
        k = k - 1
    return res

Use Ok to test your code:

python3 ok -q falling✂️

Q7: Sum Digits

Write a function that takes in a nonnegative integer and sums its digits. (Using floor division and modulo might be helpful here!)

def sum_digits(y):
    """Sum all the digits of y.

    >>> sum_digits(10) # 1 + 0 = 1
    1
    >>> sum_digits(4224) # 4 + 2 + 2 + 4 = 12
    12
    >>> sum_digits(1234567890)
    45
    >>> a = sum_digits(123) # make sure that you are using return rather than print
    >>> a
    6
    """
    "*** YOUR CODE HERE ***"
    res = 0
    while y:
        tmp = y % 10
        y = y // 10
        res = res + tmp
    return res

Use Ok to test your code:

python3 ok -q sum_digits✂️

Submit

Make sure to submit this assignment by running:

python3 ok --submit

Extra Practice

These questions are optional and will not affect your score on this assignment. However, they are great practice for future assignments, projects, and exams. Attempting these questions can be valuable in helping cement your knowledge of course concepts.

Q8: WWPD: What If?

Use Ok to test your knowledge with the following “What Would Python Display?” questions:

python3 ok -q if-statements -u✂️

Hint: print (unlike return) does not cause the function to exit.

>>> def ab(c, d):
...     if c > 5:
...         print(c)
...     elif c > 7:
...         print(d)
...     print('foo')
>>> ab(10, 20)

______
>>> def bake(cake, make):
...     if cake == 0:
...         cake = cake + 1
...         print(cake)
...     if cake == 1:
...         print(make)
...     else:
...         return cake
...     return make
>>> bake(0, 29)

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>>> bake(1, "mashed potatoes")

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Q9: K-Occurrence

Complete k_occurrence, a function which returns the number of times the digit k appears in num. 0 is considered to have no digits.

def k_occurrence(k, num):
    """
    >>> k_occurrence(5, 10)  # .Case 1
    0
    >>> k_occurrence(5, 5115)  # .Case 2
    2
    >>> k_occurrence(0, 100)  # .Case 3
    2
    >>> k_occurrence(0, 0)  # .Case 4
    0
    """
    "*** YOUR CODE HERE ***"
    occurrences = 0
    while num:
        if num % 10 == k:
            occurrences += 1
        num = num // 10
    return occurrences

To work on this problem, open the Parsons editor:

python3 parsons

Q10: Double Eights

Write a function that takes in a number and determines if the digits contain two adjacent 8s.

def double_eights(n):
    """Return true if n has two eights in a row.
    >>> double_eights(8)
    False
    >>> double_eights(88)
    True
    >>> double_eights(2882)
    True
    >>> double_eights(880088)
    True
    >>> double_eights(12345)
    False
    >>> double_eights(80808080)
    False
    """
    "*** YOUR CODE HERE ***"
    cnt = 0
    while n:
        if n % 100 == 88:
            n = n // 100
            cnt = cnt + 2
        else:
            n = n // 10
    if cnt % 2 == 0 and cnt != 0:
        return True
    else: 
        return False

Use Ok to test your code:

python3 ok -q double_eights