Lecture-12 Selection_Boolean_ 24-25

Page 1: Introduction

• COMP101 Introduction to Programming 2024-25

  • Lecture 12: Selection and Boolean

Page 2: Boolean Type

• Data Types in Programming

  • Programming languages feature various data types, which may vary in number.

  • Common data types:

    • Integer

    • Float

    • String

    • Boolean (bool)

  • Boolean Types:

    • Always evaluate to True or False.

    • Utilize comparison operators and Boolean operators:

      • Comparison operators: ==, != or <>, >, <, >=, <=

      • Boolean operators: and, or, not

      • Used to create compound conditions.

Page 3: Comparison Operators

• Function: Evaluation in selection statements returns True or False.

• Types of Comparison Operators:

  • ==: Equal to (2 == 2 is True)

  • != or <>: Not equal to (2 != 3 is True)

  • >: Greater than (2 > 1 is True)

  • <: Less than (2 < 3 is True)

  • >=: Greater than or equal to (2 >= 2 is True)

  • <=: Less than or equal to (2 <= 2 is True)

Page 4: Comparison Operators: Opposites

• Opposite Operators:

  • == has an opposite of !=

  • > has an opposite of <=

  • < has an opposite of >=

Page 5: Boolean & Comparison Operators: Precedence

• Precedence Table (BODMAS):

  • Highest: ( ) ** * / % + -

  • Comparison Operators: <, <=, >, >=, ==, !=

  • Boolean Operators: not, and, or (lowest precedence)

Page 6: Boolean Operators: and

• Characteristics:

  • Evaluates two inputs (a, b):

    • A binary operator.

    • Evaluates to True if both a and b are True.

  • Truth Table:

    • T, T -> T

    • T, F -> F

    • F, T -> F

    • F, F -> F

Page 7: Boolean Operators: and (Range Test)

• Single Input Evaluation:

  • Can evaluate input ranges, e.g., if (a > 3 and a < 300).

  • Correct syntax requires testing both limits clearly.

  • Range Limits: 4 to 299 when using (a > 3 and a < 300).

Page 8: Boolean Operators: and (Specification Testing)

• Ineffective Tests:

  • Take care when specifying numeric ranges.

  • Clarify logic in code to avoid confusion regarding limits.

  • Example of clearer specification:

    • if (mark >= 50 and mark <= 64).

Page 9: Boolean Operators: and (Compound Expression)

• Avoid Compound Expressions:

  • Can lead to long, complicated condition checks.

  • Usage: Favor clarity with simple conditional logic structures like if-elif-else.

Page 10: Boolean Operators: or

• Characteristics:

  • Evaluates inputs (a, b):

    • A binary operator.

    • Executes if either a or b is True.

  • Truth Table:

    • T, T -> T

    • T, F -> T

    • F, T -> T

    • F, F -> F

Page 11: Boolean Operators: or (Single Input)

• Single Input Evaluation:

  • Example: if (a < 0 or a > 120).

  • Test returns True for either condition being satisfied.

  • Ensure clarity, avoiding missing inputs like if (a < 0 or > 120).

Page 12: Boolean Operators: not

• Characteristics:

  • Unary operator, evaluates a single input (a).

  • Recommended to use sparingly for clarity.

  • Truth Table:

    • T -> F

    • F -> T

Page 13: Boolean Operators: not (Pass Logic)

• Example with pass/fail Logic:

  • Using if not mark < 40: vs. if mark >= 40: for improved readability.

  • Better clarity by writing tests in positive terms.

Page 14: Comparison Operators: not (Syntax Errors)

• Input Testing Example:

  • Syntax error handling when applying not directly.

  • Equivalent clearer version using !=:

    • if x != 5:.

Page 15: Boolean Operators: Short-Circuit Evaluation

• Efficiency in Evaluation:

  • for 'and': If a is False, no need to check b.

  • for 'or': If a is True, b is not evaluated.

Page 16: Summary

• General Guidelines:

  • Avoid intricate tests and excessive use of not.

  • Favor simple, readable conditions.

  • Utilize if-elif-else for clarity over complex compound expressions.

Page 17: Python if-elif-else Example

• Code Structure Demonstration:

  • Clear hierarchical structure of if statements.

  • Example shows logical flow for month evaluation.

Page 18: Python if-elif-else Robustness

• Robust Code Example:

  • Clear handling of different month cases.

  • Shows effective elimination of false cases for improved logic.