if statements

CMPUT 175 Python Review: Decision-Making and Branching

Introduction to Conditionals

• Emphasis on decision-making and branching in Python.

• Known as "if statements."

• Definition: Execute instructions if a condition is true.

Understanding Conditions

• If Statements: Basic structure

  • Format: if condition: execute instructions

  • Execute when the condition is verified.

• Else Clause: Executes if the condition is false.

  • Format: else: execute other instructions

  • Note: Else is optional.

Syntax of If Statements

• Basic Syntax in Python:

  • `if condition:

    Indented code block`

  • Code after colon must be indented to signal execution when true.

Example Scenario: Store Receipt

• Use Case: Print a receipt with discounts based on purchase amounts.

• Rule: 5% discount for purchases $300 or more.

• Variable: subtotal representing total purchase amount.

  • Example 1: subtotal = 80

    • Condition: subtotal > 300 → FALSE

  • Example 2: subtotal < 300

    • Condition: TRUE

  • Equality Check Mistake:

    • Incorrect: subtotal = 300 (assignment)

    • Correct: subtotal == 300 (comparison) → FALSE

  • Difference Check: subtotal != 300 → TRUE.

Using Conditions in Programs

• Example Implementation:

  • Initialize discount = 0

  • Check: if subtotal >= 300:

    • Calculate: discount = subtotal * 0.05

    • Result for Subtotal 80: discount = 0

  • When subtotal = 400:

    • Discount calculation results in discount = 20

Else Clause for Conditional Logic

• Complete implementation can look like:

  • if subtotal >= 300: discount = subtotal * 0.05 else: discount = 0

• Verified Again with a subtotal = 400, yields $20 discount.

Control Flow in Python

• Conditions can be any expressions returning TRUE or FALSE.

• Logical Operators:

  • Negation: NOT

  • Conjunction: AND (both conditions must be true)

  • Disjunction: OR (at least one condition must be true)

• Example Condition: if subtotal >= 100 and hasMembership:

• Control flow example with multiple conditions:

  • Structure: if condition_1: instructions elif condition_2: instructions elif condition_3: instructions else: other instructions

Elif Clause

• Elif: Represents "else if"

• Additional discount tier: 2% for purchases between $100 and $300.

  • Example with subtotal = 150

    • Check if greater than 300 (FALSE), then check if greater than 100 (TRUE).

    • Resulting discount: 150 * 0.02 → $3

Summary

• Reviewed control flow using if statements.

• Discussed conditions as expressions that yield TRUE or FALSE.

• Covered syntax and practical examples with the use of if, elif, and else clauses.