Lecture-14 Selection_Nested_2024-25

Lecture Overview

• COMP101 Introduction to Programming

• Topic: Selection in Programming

• Focus: Nested Selection Structures

Page 1: Introduction to Nested Selection

• Lecture-14: Focus on Nested if Statements.

Page 2: Nested if Structure

• Candidates for election must be:

  • Female

  • Minimum age: 21

• Code snippet:

  candidate = input("Candidate gender: ")
  age = int(input("Enter age of candidate: "))
  if candidate == "female":
      if age >= 21:
          print("female 21 or over")
          print("accept")
      else:
          print("female, but not 21")
          print("dismiss")
  else:
      print("Not female")
      print("construct exited")

• Execution Process:

  • Outer if executes if candidate is 'female'.

  • Inner if checks if age is >= 21.

  • Else statements provide feedback based on conditions not met.

Page 3: Nested if Compound Statement

• New code structure:

  if candidate == "female" and age >= 21:
      print("female 21 or over - accept")
  elif age < 21:
      print("Underage - not yet 21 - dismiss")
  else:
      print("Candidate not female - dismiss")

• Explanation:

  • if executes when both checks are true.

  • elif tests another condition when if fails.

  • else captures any failure cases.

Page 4: Compound Statement Enhanced

• Revised code structure:

  if candidate == 'female' and age >= 21:
      print("female 21 or over - accept")
  elif candidate == 'female' and age < 21:
      print("Female but underage - dismiss")
  else:
      print("Candidate not female - dismiss")

• Summary:

  • Each elif tests specific conditions to clarify checks made in if.

Page 5: Testing Conditions

• Test Cases and Expected Results:

  Input (gender, age)	Expected	Actual
  female, 21	accept	accept
  female, 22	accept	accept
  female, 20	dismiss	dismiss
  male, 21	dismiss	dismiss
  male, 22	dismiss	dismiss
  male, 20	dismiss	dismiss

• Testing Considerations:

  • Evaluates 3 conditions, minimum of 6 tests needed.

Page 6: Nested if Using Elif

• Initial versus improved structure:

  # Initial
  if score >= 90:
      print("A")
  else:
      if score >= 80:
          print("B")
  ...
  # Improved
  if score >= 90:
      print("A")
  elif score >= 80:
      print("B")
  ...

• Benefits of using elif:

  • Cleaner structure.

  • Reduces deep nesting.

Page 7: Color Input Example

• Code snippet for colour detection:

  colour = input("Enter a colour from the spectrum: ")
  if len(colour) <= 6:
      if len(colour) == 3:
          print("Colour is red")
      elif len(colour) == 4:
          print("Colour is blue")
      ...
  else:
      print("Colour is not in spectrum")

Page 8: Dog Age Calculation

• Example for calculating human age equivalent:

  dog_Age = int(input ("Dog's age?: "))
  if dog_Age == 1:
      print("14 years human")
  elif dog_Age == 2:
      print("22 years human")
  elif dog_Age > 2:
      human_Age = (22 + (dog_Age - 2) * 5)
      print(human_Age)
  else:
      print ("Too old")

Page 9: Initial Draft for UK Origin

• Example to determine where person was born:

  bornIn = input("Where in the UK where you born?: ")
  if bornIn == "England":
      print("You are English")
  elif bornIn == "Ireland":
      ...
  else:
      print("You are Welsh")

• Discussion of logic failures in the structure.

Page 10: Second Draft Handling Input Case

• Enhanced case handling:

  bornIn = input("Where in the UK where you born?: ").lower()
  ...

• Implementing boolean operators to cover variations in input case.

Page 11: Upper/Lower Case Standardization

• Final recommended structure:

  bornIn = input("Where in the UK where you born?: ").upper()
  if bornIn == "ENGLAND":
      print("You are English")
  ...

• Ensuring consistency and functionality regardless of input case.

Page 12: Dangling Else Problem

• Logic Error:

  • Caused by unintended interactions of indents.

  • Suggested to add an additional else for clarity and debugging.

Page 13: Elaborating on Dangling Else

• Revised Approach:

  • Each if should correspond to an else for better logical clarity.

Page 14: Complicated Conditional Structure

• Overview of complex conditions:

  • Tests should focus on clear paths for execution.

• Need for testing and clarity in logic due to complexity.

Page 15: Flowchart Testing

• Importance of 100% decision coverage:

  • Tests for conditions A, D, E, F.

Page 16: Implementing Flowchart Test Cases

• Scenario Testing for inputs and expected outcomes

• Ensures that all logic paths are covered in conditions to ensure robust testing.