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Branching and Choice

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Objectives

  • Why use branching?
  • Branching structures in Python
  • Practice

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Why Use Branching?

The Challenges of Choice

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Branching Allows Choice

  • Most programs require choices
  • Different behaviour leads to different paths through the program
  • Primary mechanism is the if keyword
  • Combines with conditions that evaluate to True or False

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Simplest Branching

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Branching Structures in Python

How Do We Branch?

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Python Branches

  • Simplest approach using if keyword

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  • Can be extended with else keyword

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More Complicated Branches

  • Can also use elif keyword
  • Can have as many elif’s as necessary

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Practice

Putting it all together!

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Example 1: Even and Odd

  • How do we know if an integer is even?

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Example 1: Even and Odd

  • How do we know if an integer is even?
  • If it is divisible by 2, then it is even
    • Otherwise, it is odd
  • This suggests branching!

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  • Use the mod operator (%)
  • 23 % 5 = 3 since 23 = 4x5 + 3
  • Consider the same thing with % 2

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  • Complete L1.5 Even and Odd

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Example 1: Even and Odd

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Teacher solution

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Example 2: Classifying Numbers

  • Any integer can be positive, negative, or zero
  • Make a program that gets an integer from the user and then determines if the number is positive, negative, or zero

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Example 2: Classifying Numbers

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Additional Practice

  • L1.4 Branching 1
  • L1.5 Even and Odd
  • L1.6 Tall Person

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Teacher Solution L1.04

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CREDITS

Special thanks to all the people who made and released these awesome resources for free:

  • Presentation template by SlidesCarnival

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