Chapter 5: Conditional Statements

5.1 Chapter Overview

Conditional statements allow a Python program to make decisions. In real life, decisions are made every day: if marks are above the passing score, the student passes; if payment is completed, registration is confirmed; if attendance is enough, the student is eligible for a certificate.

In programming, conditional statements control which block of code should run based on whether a condition is True or False.

5.2 Chapter Objectives

• Understand the purpose of conditional statements.
• Use if statements to execute code based on a condition.
• Use if-else statements for two-way decisions.
• Use if-elif-else statements for multiple decisions.
• Apply comparison operators in conditions.
• Combine multiple conditions using logical operators.
• Develop interactive Python applications using decision logic.

Learning Outcomes

• Write Python programs that make decisions.
• Use indentation correctly in conditional statements.
• Create pass/fail, grade, eligibility and fee decision programs.
• Apply nested conditional statements in practical examples.

5.3 What is Decision Logic?

Decision logic is the process of checking a condition and choosing what action to perform. A condition is an expression that gives a result of either True or False.

Example Condition

marks >= 50

If marks are 50 or above, the condition is True. If marks are below 50, the condition is False.

5.4 Comparison Operators Used in Conditions

5.5 The if Statement

The if statement is used when a block of code should run only if a condition is True.

Syntax

if condition:
    statement

Example

marks = 80

if marks >= 50:
    print("You have passed.")

5.6 The if-else Statement

The if-else statement is used when there are two possible actions. If the condition is True, the if block runs. Otherwise, the else block runs.

Syntax

if condition:
    statement_if_true
else:
    statement_if_false

Example: Pass or Fail

marks = 45

if marks >= 50:
    print("Pass")
else:
    print("Fail")

5.7 Taking User Input with if-else

Conditional statements become more useful when combined with user input.

marks = float(input("Enter your marks: "))

if marks >= 50:
    print("Result: Pass")
else:
    print("Result: Fail")

5.8 The if-elif-else Statement

The if-elif-else statement is used when a program has more than two possible decisions.

Syntax

if condition1:
    statement1
elif condition2:
    statement2
elif condition3:
    statement3
else:
    final_statement

Example: Grade System

marks = float(input("Enter marks: "))

if marks >= 80:
    print("Grade A")
elif marks >= 65:
    print("Grade B")
elif marks >= 50:
    print("Grade C")
else:
    print("Fail")

5.9 Order of Conditions

In an if-elif-else structure, Python checks conditions from top to bottom. Once a True condition is found, Python executes that block and skips the rest.

5.10 Nested Conditional Statements

A nested conditional statement means placing one if statement inside another if statement. This is used when a second decision depends on the first decision.

Example: Certificate Eligibility

marks = float(input("Enter marks: "))
attendance = float(input("Enter attendance percentage: "))

if marks >= 50:
    if attendance >= 80:
        print("Eligible for certificate")
    else:
        print("Not eligible due to low attendance")
else:
    print("Not eligible due to failed marks")

5.11 Logical Operators in Conditional Statements

Logical operators are used to combine multiple conditions.

Example using and

marks = float(input("Enter marks: "))
attendance = float(input("Enter attendance: "))

if marks >= 50 and attendance >= 80:
    print("Eligible for certificate")
else:
    print("Not eligible for certificate")

5.12 Real-World Example: Login Decision

Conditional statements are commonly used in login systems to check username and password.

username = input("Enter username: ")
password = input("Enter password: ")

if username == "admin" and password == "pdtc123":
    print("Login successful")
else:
    print("Invalid username or password")

5.13 Real-World Example: Course Fee Status

This example checks whether a student has completed fee payment.

course_fee = float(input("Enter course fee: "))
amount_paid = float(input("Enter amount paid: "))

balance = course_fee - amount_paid

if balance <= 0:
    print("Payment completed")
else:
    print("Outstanding Balance: RM", balance)

5.14 Common Beginner Mistakes

5.15 Hands-On Practice

5.16 Final Assessment Quiz

Answer the following questions. Correct Answer = +1 Mark Wrong Answer = -0.5 Mark

Final Practical Assessment

Develop an interactive Python program named certificate_eligibility.py. The program must ask for student name, marks and attendance percentage. It must display whether the student is eligible for certificate, not eligible due to marks, or not eligible due to attendance.

5.17 Chapter Summary

In this chapter, learners studied conditional statements in Python. They learned how to use if, if-else, if-elif-else, nested conditions, comparison operators and logical operators to create decision-making programs.