CSE 160 Section 2

Loops and Range, If statements!

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CSE 160

CSE 160: Section 2

Logistics

• How was HW0? Everything has been set up?

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• HW1 (due Thurs Jan 22 @ 11:59pm)
• Submitting file on Gradescope - don’t change the file name!
• Wait for autograder!

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• Programming practice 2 (due Wed Jan 21 @ 11:59pm)

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• Written Check-in 2 (due Friday Jan 16 @ 11:59pm)

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CSE 160: Section 2

Hw 1 Tips

• Reminders:
• To run the file: python FILE_NAME.py
• Check for formatting errors - flake8: flake8 FILE_NAME.py
• Don’t change the filenames!
• Your output should exactly match the expected output.
• blanks should be replaced with your answers

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Diffchecker.com

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CSE 160: Section 2

DiffChecker Example

Diffchecker.com

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Problem 1 solution follows:

Root 1: ____

Root 2: ____

Problem 1 solution follows:

Root 1 : ____

Root 2 : ____

CSE 160: Section 2

DiffChecker Example

Diffchecker.com

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Problem 1 solution follows:

Root 1: ____

Root 2: ____

Problem 1 solution follows:

Root 1 : ____

Root 2 : ____

CSE 160: Section 2

If / Else Overview

CSE 160: Section 2

If/ Else Structure

• Checks that condition is True/False, and executing code based on that condition

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is_raining = True

is_sprinkling = False

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if is_raining:

print(“Bring an umbrella”)

elif is_sprinkling:

print(“Bring a raincoat”)

else:

print(“Bring sunglasses”)

CSE 160: Section 2

If/ Else Structure

• Checks that condition is True/False, and executing code based on that condition

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is_raining = True

is_sprinkling = False

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if is_raining:

print(“Bring an umbrella”)

elif is_sprinkling:

print(“Bring a raincoat”)

else:

print(“Bring sunglasses”)

Output:

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Bring an umbrella

CSE 160: Section 2

Lecture Review: Loops

CSE 160: Section 2

Loops

• Any variable name can be used in place of i (for good style, pick a variable name that fits the context)
• Indentation is a requirement to indicate loop body

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

print(i)

PythonTutor

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CSE 160: Section 2

Loops

• Avoid redundancy
• More readable
• Avoid bugs
• Can easily make changes in code body,

or number of times loop is repeated

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CSE 160: Section 2

Nested Loops Overview

CSE 160: Section 2

Nested Loops

• A for loop within the body of another for loop

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Example:

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

for j in [0, 1, 2]:

print(i)

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CSE 160: Section 2

Nested Loops

• Nested loop structure
• Outer loop
• Inner loop

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

for j in [0, 1, 2]:

print(i)

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• Variable names i and j should be different for clarity

CSE 160: Section 2

Nested Loops

• Lets see what this outputs!

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Example:

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

for j in [0, 1, 2]:

print(i)

PythonTutor

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CSE 160: Section 2

Lecture Review: Range

CSE 160: Section 2

Range

• range(start, stop, step)
• range(start, stop)
• (inclusive, exclusive)
• Step is assumed to be 1
• range(stop)
• (exclusive)
• Step is assumed to be 1; Start is assumed to be 0

Example: range(0, 6, 2) loops through [0, 2, 4]

Equivalent to: range(0, 5, 2)

Python Tutor

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CSE 160: Section 2

Kahoot!

Link

CSE 160: Section 2

Section Handout Problems

CSE 160: Section 2

Lists, Ranges, and Loops

3. 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. Your output should read:

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24

27

30

33

36

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CSE 160: Section 2

Lists, Ranges, and Loops

3. Possible solutions appear below:

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for value in [8, 9, 10, 11, 12]:

print(3 * value)

for value in range(8, 13):

print(3 * value)

for value in range(24, 37, 3):

print(value)

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CSE 160: Section 2

Nested Loops

4. What is the output printed by the following program?

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sum = 0

for i in [1, 2, 3]:

for j in [1, 2, 3]:

sum = sum + i

print(sum)

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Answer: Python Tutor

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CSE 160: Section 2

Additional Practice Problems

CSE 160: Section 2

Lists, Ranges, and Loops

6. What is the output printed by the following program?

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for value in [1, 3, 5]:

print(value + value ** 2)

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CSE 160: Section 2

Lists, Ranges, and Loops

6. What is the output printed by the following program?

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for value in [1, 3, 5]:

print(value + value ** 2)

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Output:

2

12

30

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CSE 160: Section 2

Nested Loops

7. What is the output printed by the following program?

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for i in [1, 2, 3]:

for j in [1, 2, 3]:

print(i + j)

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Answer: Python Tutor

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CSE 160: Section 2

Nested Loops

8. Write code to print the number of people over 20 years old in the list ages

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ages = [20, 21, 20, 22, 19, 18, 14, 35]

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CSE 160: Section 2

Nested Loops

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ages = [20, 21, 20, 22, 19, 18, 14, 35]

count = 0

for age in ages:

if (age > 20):� count += 1

print(count)

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CSE 160: Section 2

Written Check-In

Due Friday @ 11:59pm

CSE 160: Section 2