CS 104:

Introduction to Computers and Ethics

For Loops

Announcements & Reminders

• Homework 3 grades on Blackboard
• Homework 5 due Friday, Sep 30
• Can submit up to 3 days late for 10% off per day
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• You should apply, even if you don’t feel you have enough experience yet!
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Announcements & Reminders

• Opportunity to get points back on your quiz
• Quiz reopened Tuesday evening until Friday evening
• You can re-submit coding questions (not multiple choice), but must include in a comment what you learned that you did not know at the time of the quiz

# I didn’t know what return does, but I have since learned that it does…x, y, z

• Feel free to ask questions in office hours
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Announcements & Reminders

• Darian (Google recruiting partner for Alabama A&M) will be visiting campus on Monday, Oct 3!
• Office hours w/ Darian from 12:30-3:30 in my office (AJB 320)
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• This event is targeted towards ALL years (not just those applying to STEP)

in operator

in operator: checks if value exists in sequence

in expression evaluates to True if value exists

word = 'banana'

if 'n' in word:

print('Found an n')

else:

print('Did not find a n')

Practice: in operator

'n' in 'Nashville, TN'

'N' in 'Nashville, TN'

True

False

True

False

char = ' '

char in 'Intro to Computer Science'

word = 'CS104'

char in word

for loops

for loop: control structure that runs block of code repeatedly by iterating over elements in sequence

for letter in 'cat':

print(letter)

Tracing for loops

for letter in 'cat':

print(letter)

print('done')

​

'c'

letter

Tracing for loops

for letter in 'cat':

print(letter)

print('done')

​

'c'

letter

c

Tracing for loops

for letter in 'cat':

print(letter)

print('done')

​

'a'

letter

c

Tracing for loops

for letter in 'cat':

print(letter)

print('done')

​

'a'

letter

c

a

Tracing for loops

for letter in 'cat':

print(letter)

print('done')

​

't'

letter

c

a

Tracing for loops

for letter in 'cat':

print(letter)

print('done')

​

't'

letter

c

a

t

Tracing for loops

for letter in 'cat':

print(letter)

print('done')

​

't'

letter

c

a

t

No elements left!

Tracing for loops

for letter in 'cat':

print(letter)

print('done')

​

't'

letter

c

a

t

done

for vs while

Similarity: repeating code in a loop

Difference:

while loop goes until condition is no longer met

for loop goes for a predetermined / known number of times

for vs while

​

for letter in word:

print(letter)

​

print('All done!')

index = 0

while index < len(word):

print(word[index])

index = index + 1

print('All done!')

range()

range(): returns sequence from start to end (not including end)

Use range() with for loops to repeat a loop when need numbers

​

​

range(5, 8)

range(0, 5)

range(5)

5 6 7

0 1 2 3 4

0 1 2 3 4

range()

range(): returns sequence from start to end (not including end)

Use range() with for loops to repeat a loop when need numbers

​

​

i = 0

while i < 10:

print(i)

i = i + 1

​

for i in range(0, 10):

print(i)

these are equivalent!

Tracing for loops

for num in range(3, 5):

print(num)

print('exited loop')

num

Tracing for loops

for num in range(3, 5):

print(num)

print('exited loop')

3

num

Tracing for loops

for num in range(3, 5):

print(num)

print('exited loop')

3

num

3

Tracing for loops

for num in range(3, 5):

print(num)

print('exited loop')

4

num

3

Tracing for loops

for num in range(3, 5):

print(num)

print('exited loop')

4

num

3

4

Tracing for loops

for num in range(3, 5):

print(num)

print('exited loop')

4

num

3

4

Reached 5. Nothing left!

Tracing for loops

for num in range(3, 5):

print(num)

print('exited loop')

4

num

3

4

exited loop

Try it yourself: write a for loop that sums the numbers 1 to 10, and then prints out the answer

​

*use range!

sum_1_to_10 = 0

for i in range(1, 11):

sum_1_to_10 += i

print(sum_1_to_10)

for … in ...

for … in range(...)

for [variable] in [sequence]:

[code]

for [variable] in range(...):

[code]

Iterating over a sequence, like a string

​

for letter in 'dog'

letter will be each character in 'dog'

Iterating over numbers

​

for number in range(10)

number will be a number from 0 to 10

Break

• break is used to stop and exit loops early

0

1

​

​

​

CONSOLE:

Continue

• continue is used to skip the current loop iteration and go back to check the loop condition

0

1

3

​

​

CONSOLE: