A201/A597 Introduction to Programming I (4/3 cr.)

First Summer 2006

Lab Ten: Exercises (in random order).

What does this method do?

def what(n1, n2):
    return (n1 > n2) * n1 + (n2 > n1) * n2

What does this method do?

def what(n):
    if n == 0:
        return 0
    else:
        return n + what(n-1)

What does this method do?

def what(n, m):
    if n == 1:
        return m
    else:
        return what(n-1, m) + m

Let's go back to a previous problem and examine it closely:

def what(n):
    if n == 0:
        return 0
    else:
        result = n + what(n-1)
        return result

Let's ask two questions:

what if we print n before the variable result is calculated?
what if we print n after the variable result is calculated?

Try it either way:

def what(n):
    if n == 0:
        return 0
    else:
        # print n
        result = n + what(n-1)
        # print n
        return result

In both cases the question, of course, is: why?

What does the following method print?

def play():
    j = 0  
    for i in range(10):
      while j < i: 
        print j
        j = j + 1

Now let's make a change, and move j = j + 1 to the left one tab.

def play():
    j = 0  
    for i in range(10):
      while j < i: 
        print j
      j = j + 1

Finally, let's move that line one more tab to the left. What gets printed then?

def play():
    j = 0  
    for i in range(10):
      while j < i: 
        print j
    j = j + 1

Here's a question with which we could and maybe should have started:

def f(x):
    return g(x) + (h(x) ** 0.5)

def g(x): 
    return 4 * h(x)

def h(x): 
    return x * x + k(x) - 1

def k(x): 
    return 2 * (x + 1)

Given the definitions above, what does this line print:

print k(g(2) + h(2))

Now consider the code fragment below:

i = 2
while i < 10: 
  print i
  i = i + 2

Which of the following fragments are equivalent to it? (Check all that apply.)

for i in range(2, 10, 2): 
  print i

for i in range(1, 9, 2): 
  print i + 1

i = 2
while i <= 8: 
  i += 2 
  print i

i = 1
while i < 5: 
  i = i + 1
  print 2 * i

for i in range(2, 10): 
   print i
   print i + 2

Consider the following code fragment when embedded in a complete program:

if x > 3: 
  if x <= 5: 
    y = 1
  elif x != 6: 
    y = 2
else:
    y = 3

Assume that x has a value of 6 at the beginning of the fragment.

What value does the variable y hold after the fragment gets executed?

1
2
3
6
impossible to determine from the information given

Which of the following are infinite loops? Check all that apply:

count = 0
while count > 0:
   print count
   count = count + 1

i = 0
while i < 10:
  print i
  i = i - 1

i = 1
while i != 10:
  i = i + 2
  print i

x = 0
if x >= 0: 
   print x
   x = x + 1

x = 0
while x == 0:
   x = x + 1
   print x
   x = 0

Consider the following two program fragments and assume that x holds an integer.

# fragment 1     |          # fragment 2
                 |
if x == 5:       |         if x == 5:
   x = x + 1     |            x = x + 1
else:            |         if x != 5:
   x = 8         |            x = 8

Which of these statements is true?

The two fragments are logically equivalent.
If x is 6 initially, then
1. the value in x is 8 after executing fragment 1 and
2. the value in x is 6 after executing fragment 2.
Fragment 2 contains a syntax error.
x always has the value 8 after executing fragment 2.
x has either the value 5 or the value 8 after executing fragment 1.