Control Structures: exam

If you need help reviewing Control Structures, take a look at these resources:

Albert and Robert's slides

Albert and Robert's slides part 2

Each question has a "Toggle Solution" button -- click it to reveal that question's solution.

What would Python print?

Question 1

The following code is loaded into the Python interpreter

def is_even(x):
    if x % 2 == 0:
        print('even')
    print('odd')
    return x - 1

def branch(x):
    if x > 5:
        print('one')
    elif x > 0:
        print('two')
    if x > 10:
        print('three')
    else:
        print('four')
    return x + 5

What would Python print for the following lines?

>>> a = is_even(4)
______even
odd
>>> b = branch(20)
______one
three
>>> c = branch(3)
______two
four
>>> d = is_even(is_even(5))
______odd
even
odd
>>> e = branch(branch(3))
______two
four
one
four

Code-Writing questions

Question 2

Implement a function is_ascending, which takes in a number n. is_ascending returns True if the one's digit of n is less than or equal to the ten's digit, and the ten's digit is less than or equal to the hundred's digit, and so on. In other words, the digits of the number going from right to left must be in ascending order.

def is_ascending(n):
    """Returns True if the digits of N are in ascending order.

    >>> is_ascending(321)
    True
    >>> is_ascending(123)
    False
    >>> is_ascending(4432221)
    True
    >>> is_ascending(5492)
    False
    >>> is_ascending(5420)
    True
    """
    "*** YOUR CODE HERE ***"

def is_ascending(n):
    largest = 0
    while n > 0:
        ones = n % 10
        if ones < largest:
            return False
        largest = ones
        n = n // 10
    return True

Question 3

Implement a function count_one, which takes in a number n, and returns the number of ones in the digits of n.

def count_one(n):
    """Counts the number of 1s in the digits of n

    >>> count_one(7007)
    0
    >>> count_one(123)
    1
    >>> count_one(161)
    2
    >>> count_one(1)
    1
    """
    "*** YOUR CODE HERE ***"

def count_one(n):
    count = 0
    while n > 0:
        if n % 10 == 1:
            count += 1
        n = n // 10
    return count

Question 4

Implement a function total_one, which takes in a number n, and returns the number of ones in the digits of all numbers from 1 to n.

Hint: You can use the count_one function from above.

def total_ones(n):
    """Returns number of 1s in the digits of all numbers from 1 to
    n.

    >>> total_ones(10) # 1, 10 -> two 1s
    2
    >>> total_ones(15) # 1, 10, 11, 12, 13, 14, 15 -> eight 1s
    8
    >>> total_ones(21)
    13
    """
    "*** YOUR CODE HERE ***"