Python if Statement (CBSE Class 11 Computer Science)

In real life, we make decisions every day based on certain conditions. For example, a student is allowed to appear for an examination only if the attendance is at least 75%. Similarly, Python uses the if statement to execute a block of code only when a specified condition is True.

Learning Objectives

• Understand decision making in Python.
• Learn the syntax of the if statement.
• Understand flowchart representation.
• Trace the execution of an if statement.
• Write simple decision-making programs.

Quick Syntax Reference

if condition:
    statement(s)

What is the if Statement?

The if statement is a conditional statement that executes a block of code only if the given condition evaluates to True. If the condition is False, the block is skipped.

Flowchart

          Start
            │
            ▼
     Check Condition
            │
      ┌─────┴─────┐
      │           │
    True        False
      │           │
      ▼           │
 Execute Block    │
      │           │
      └─────┬─────┘
            ▼
           End

Algorithm

1. Start.
2. Evaluate the condition.
3. If the condition is True, execute the statements inside the if block.
4. If the condition is False, skip the block.
5. Stop.

Pseudocode

IF condition is True THEN

    Execute statements

END IF

Example 1: Voting Eligibility

age = 20

if age >= 18:
    print("Eligible to Vote")

Output

Eligible to Vote

Dry Run Table

Trace Table

Example 2: Positive Number

num = -8

if num > 0:
    print("Positive Number")

Output

No Output

Since the condition is False, the if block is skipped.

Program Flow

Condition True
      │
      ▼
Execute Block
      │
      ▼
Continue Program

Condition False
      │
      ▼
Skip Block
      │
      ▼
Continue Program

Think Like a Programmer

Predict the output.

marks = 45

if marks >= 33:
    print("Pass")

print("Exam Completed")

Pass
Exam Completed

Output Prediction Challenge

x = 5

if x > 10:
    print("Greater")

print("Done")

Done

Debugging Exercise

Find and correct the error.

age = 18

if age >= 18
    print("Eligible")

Error: Missing colon (:) after the if condition.

Competency-Based Question

A school allows students to participate in an inter-school competition only if they have secured at least 60% attendance. Write a Python program using an if statement to display "Eligible" if attendance is 60 or above.

Real-Life Example

• If it is raining, carry an umbrella.
• If the traffic signal is green, move ahead.
• If your attendance is at least 75%, you can appear for the examination.

Common Beginner Mistakes

• Forgetting the colon (:).
• Incorrect indentation.
• Using = instead of == when comparing values.
• Expecting output even when the condition is False.

Visual Memory Box

Memory Trick

Exam Tips

• Always end the if statement with a colon.
• Maintain proper indentation.
• Practice output-based questions.
• Remember that the block executes only when the condition is True.

CBSE Important Questions

2 Marks

1. What is the purpose of the if statement?
2. Why is indentation necessary in an if statement?

3 Marks

1. Explain the syntax and working of the if statement with an example.
2. Draw the flowchart of an if statement.

5 Marks

1. Write a Python program using the if statement to determine voting eligibility and explain its execution with a dry run.

Practice Yourself

1. Write a program to check whether a number is positive.
2. Write a program to check if a student has passed (marks ≥ 33).
3. Write a program to check whether a person is eligible for voting.
4. Trace the execution of an if statement for different inputs.
5. Create your own real-life example using an if statement.

Frequently Asked Questions (FAQs)

1. What happens if the condition is False?

The statements inside the if block are skipped.

2. Is indentation compulsory?

Yes. Python uses indentation to identify code blocks.

3. Can an if statement contain more than one statement?

Yes. All statements with the same indentation belong to the if block.

4. Can we use relational and logical operators in an if condition?

Yes. Conditions can use relational, logical, membership, and identity operators.

5. What is the syntax of the if statement?

if condition: followed by an indented block of statements.

Summary

• The if statement is used for decision making in Python.
• The block executes only when the condition evaluates to True.
• A colon (:) and proper indentation are mandatory.
• Flowcharts, dry runs, and trace tables help understand program execution.
• The if statement forms the foundation for more advanced conditional statements such as if-else and if-elif-else.