Welcome to CSE 160! Week 2

Section AA with Andre

Agenda

1. Recap: if statements, for loops, range
2. Practice problems
3. Mini-Project: password cracking

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Goals:

• Gain better familiarity with if statements, for loops, and range
• Grasp the power of sheer computational brute force
• …and how to design systems resistant to it

Logistics

• HW0 was due yesterday, Wed. Jan 10
• Week 2 Programming Check-In due Mon. Jan 15
• HW1 has been released and is due on Wed. Jan 17

For loops

for i in [0, 1, 2, 3]:

print(i)

• You can pick any variable name in place of “i”
• Indentation is important
• Motivation: loops let you avoid repeating code, which makes
• code more readable,
• avoids bugs,
• makes it easy to quickly change program details

range

syntax: range(start [inclusive], stop [exclusive], step)

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for i in range(5): # equivalent to range(0, 5, 1)

print(“hi!”)

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[out]:

hi!

hi!

hi!

hi!

hi!

range

syntax: range(start [inclusive], stop [exclusive], step)

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for i in range(5): # equivalent to range(0, 5, 1)

print(i)

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[out]:

0

1

2

3

4

range

syntax: range(start [inclusive], stop [exclusive], step)

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for i in range(3, 5): # equivalent to range(3, 5, 1)

print(i)

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[out]:

3

4

range

syntax: range(start [inclusive], stop [exclusive], step)

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for i in range(0, 10, 2):

print(i)

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[out]:

0

2

4

6

8

range

syntax: range(start [inclusive], stop [exclusive], step)

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for i in [‘apple’, ‘banana’, ‘orange’]:

print(i + ‘s’)

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[out]:

apples

bananas

oranges

range

syntax: range(start [inclusive], stop [exclusive], step)

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for letter in “five”:

print(letter)

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[out]:

f

i

v

e

range

syntax: range(start [inclusive], stop [exclusive], step)

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for letter in “five”:

print(letter * 5)

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[out]:

fffff

iiiii

vvvvv

eeeee

Practice Problem #1

Write a for loop that will print the result of multiplying 3 by the numbers 8 through 12. The example solution is two lines long.

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[out]:

24

27

30

33

36

Practice Problem #1

Write a for loop that will print the result of multiplying 3 by the numbers 8 through 12. The example solution is two lines long.

​

[out]:

24

27

30

33

36

Practice Problem #2

Write the output to the following program:

for i in [1, 2, 3]:

for j in [1, 2, 3]:

print(i + j)

Practice Problem #3

Write the output to the following program:

sum = 0

for i in [1, 2, 3]:

for j in [1, 2, 3]:

sum = sum + i

print(sum)

Mini-Project: Password Cracking

• iPhone passwords are 6 digits long.
• How long would it take for a computer to crack your password?
• Approach #1: structured search
• Approach #2: random search
• We’ll play with ways to decrease password crackability