CS 151, fall 2019
Exam 3

Points - the amount/problem is listed for each problem.  There are a total of 52 points total (4 linux commands, 4 getting around terminal, 8 python keywords, 8 python expressions, 8 short python code, 8 python functions, 8 play computer algorithms, 4 recursive function)

Please fill in the following.

0) Name:



0) Commands (1/2 point each, 4 points total)
   What is the Linux command to do each of the following?

0.1) Move a file or directory:

0.2) Delete a file: 

0.3) Print current directory:

0.4) List directory contents:

0.5) Edit a text file:

0.6) Make a new directory:

0.7) Change directories:

0.8) Copy a file:





1) Getting Around in the Terminal (1/2 point each, 4 points total)
   What is the correct thing to type for each of the following in the Linux terminal?

1.1) wildcard, used to match multiple files (one character): 

1.2) one directory higher than you are now (two characters): 

1.3) run the command just typed (one key): 

1.4) current directory (one character): 

1.5) scroll through the commands you have executed (two keys): 

1.6) auto-complete the command or file name you are typing (one key): 

1.7) top of the entire file system (like C: on Windows, one character): 

1.8) shortcut to your home directory (one character): 





2) Python keywords (8 points, 1/2 point each)
For this section answer with the appropriate python keyword(s)

2.1) Test if something is inside of a list/string/tuple/dictionary:

2.2) Special value for a variable that has no value: 

2.3) Function to convert a string to an integer:

2.4) Data type for True and False:

2.5) Boolean operator, True only if both sides are True:

2.6) Determine whether two objects are the same object(not just value):

2.7) Function to generate a sequence of numbers:

2.8) Text data type:

2.9) Loop that iterates through a list:

2.10) Keyword to send a value back from a function:

2.11) To load a module:

2.12) Function to get the length of a string:

2.13) Conditional statements (three keywords):

2.14) Declare a function:

2.15) Boolean operator, True if either side is True:

2.16) Go back to top of the loop (end the current iteration):



3) Evaluate the Python expression (8 points, 1/2 point each)
Assume the following initialization code has just run.  Write exactly what Python would print as the result of each expression.
peeps = {'ha': ['last', 'first', 'ok'],
         'bo': ['vast', 'birst', 'the'],
         'lu': ['gast', 'kirst', 'then']}
peeps['bo'][0] = 'ok'
peeps['lu'][1] = 'dokay'

msg = 'Hello world. Goodbye now.'
words = msg.split(' ')
tot = len(words)
tot2 = len(msg)

def prod(x):
  total = 1
  for y in x:
    total *= len(y)
  return total
w = 3
ww = -2.7
www = 3**2

3.1) False or False

3.2) False and True

3.3) prod(peeps['ha'])

3.4) w // 2

3.5) w < ww

3.6) str('2 + 1')

3.7) w / 2

3.8) len(msg)

3.9) 2 ** w

3.10) '3' == w

3.11) words[0]

3.12) str(2 + 1)

3.13) 'g' in msg

3.14) 'w' in msg

3.15) w % 2

3.16) peeps['bo'][0]





4) Short Python (2 points each, 8 points total)
Assume the initialization code from problem 2 has just been run.  For each of the following, give the python code to complete the task.

4.1) print how many items are in words



4.2) for each /value/ v in peeps, print v[0]




4.3) count how many times 'i' occurs in msg, print the result







4.4) set www to be ww times w




5) Python functions (4 points each, 8 points total, 4 points each)
Create a python function to do each of the following.

5.1) Parameter is an integer n, print integers from n down to 1











5.2) Parameter is a string, return how many times the - character is in the string













6) Play computer (8 points, 4 points each)

6.1) Base convert algorithm

def convertToBase(x, b):
    ans = ''
    while x > 0:
      ans = str(x % b) + ans
      x = x // b
    return ans

print(converToBase(41, 2))

Write what x is each time it changes, and x%b each time it gives a new bit of the answer

x: 



x % b:





Final value printed to screen: 




6.1) Selection Sort algorithm

def selection_sort(arr):

    for i in range(len(arr)-1):
        # index of the minimum value
        minx = i

        for j in range(i+1, len(arr)):
            if arr[j] < arr[minx]:
                minx = j

        # Swap values
        tmp = arr[minx]
        arr[minx] = arr[i]
        arr[i] = tmp

L = [5, 4, 3, 6, 2, 7]
selection_sort(L)

For each value of i, write what L is at the end of the loop inside selection_sort

i=0


i=1


i=2


i=3


i=4