Control Flow, Functions & Statements – II

 Control Flow, Functions & Statements – II

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1. What Is Control Flow?

• Every Python program runs line by line — but real problems need decisions, repetition, and organization.
• Control flow gives your code the power to decide, repeat, and reuse logic.

Example (Human Analogy):

“If it’s raining, take an umbrella.

Otherwise, wear sunglasses.”

That’s how computers make choices too!

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2. Conditional Statements (if, elif, else)

Conditional statements help your code make decisions based on True or False conditions.

Syntax:

if condition:

    # code runs when condition is True

elif another_condition:

    # runs if first is False and this is True

else:

    # runs when none are True

Example:

age = 18

if age >= 18:

    print("You can vote!")

else:

    print("Sorry, not eligible.")

✅ Output:

You can vote!

Key Points:

• Conditions use comparison operators like:

• == equal to
• != not equal
• <, >, <=, >=

Real-life analogy:

“If temperature > 30, turn on AC; else, open window.”

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3. Combining Multiple Conditions

Sometimes you need to check more than one condition together.

• and → all conditions must be true
• or → at least one must be true
• not → reverses the condition

Example:

temperature = 28

humidity = 70

if temperature > 25 and humidity > 60:

    print("It's hot and humid today!")

✅ Output:

It's hot and humid today!

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4. Loops: Automating Repetition

Loops let you repeat actions without writing the same line again and again.

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a) for Loop

Used when you know how many times to repeat.

Example:

for i in range(5):

    print("Iteration:", i)

✅ Output:

Iteration: 0

Iteration: 1

Iteration: 2

Iteration: 3

Iteration: 4

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b) while Loop

Used when you repeat until a condition changes.

Example:

count = 0

while count < 3:

    print("Count:", count)

    count += 1

✅ Output:

Count: 0

Count: 1

Count: 2

⚠️ Be careful:

If your condition never becomes False, the loop will run forever (infinite loop).

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5. Controlling Loops: break and continue

• break → stops the loop immediately
• continue → skips the current step and continues to next

Example:

for num in range(1, 6):

    if num == 3:

        continue   # skip 3

    if num == 5:

        break      # stop at 5

    print(num)

✅ Output:

1

2

4

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6. Functions: Reusable Code Blocks

Functions help organize logic into small, reusable pieces.

Syntax:

def function_name(parameters):

    # code

    return value

Example:

def greet(name):

    return f"Hello, {name}!"

print(greet("Amit"))

✅ Output:

Hello, Amit!

Why use functions?

• Saves time (write once, use many times)
• Keeps code clean and modular
• Makes debugging easier

💡 Tip:

Functions can even call other functions!

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7. Returning Values and Passing Data

Functions can return results to use elsewhere.

Example:

def add(a, b):

    return a + b

result = add(5, 3)

print("Sum:", result)

✅ Output:

Sum: 8

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8. Organizing Code with Modules

When your code becomes large, split it into multiple files called modules.

Step 1: Create a file helpers.py

def add(a, b):

    return a + b

Step 2: Use it in another file

import helpers

print(helpers.add(10, 5))

✅ Output:

15

Why use modules?

• Keeps code organized
• Allows reuse across projects
• Python already provides many built-in modules like math, os, datetime

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9. Real-Life Analogy: The Restaurant Example 🍽️

Concept	Real-life analogy
if/else	Deciding the menu (veg or non-veg)
Loops	Cooking 10 plates of pasta
Functions	Each kitchen station (salad, grill)
Modules	Different kitchens working together

Control flow makes your program work like a well-run restaurant — efficient, logical, and reusable.

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10. Common Mistakes to Avoid

❌ Forgetting colons (:) after if, elif, or for lines

❌ Wrong indentation — Python is strict about spacing

❌ Writing infinite loops accidentally

❌ Using = instead of == for comparison

✅ Always test and read your conditions carefully!

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11. Putting It All Together

Example Program:

def check_grade(score):

    if score >= 90:

        return "Excellent"

    elif score >= 75:

        return "Good"

    elif score >= 50:

        return "Average"

    else:

        return "Needs Improvement"

scores = [95, 82, 47, 60]

for s in scores:

    print(f"Score: {s}, Grade: {check_grade(s)}")

✅ Output:

Score: 95, Grade: Excellent

Score: 82, Grade: Good

Score: 47, Grade: Needs Improvement

Score: 60, Grade: Average

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12. Mini Challenge – FizzBuzz

Task:

Write a program that takes a number and:

• Prints “Fizz” if divisible by 3
• Prints “Buzz” if divisible by 5
• Prints “FizzBuzz” if divisible by both
• Otherwise prints the number

Hint:

Use % (modulus) operator and if-elif-else.

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13. Key Takeaways

Concept	Meaning
Control Flow	The logic that guides program execution
If/Else	Helps programs make decisions
Loops	Automates repetition
Functions	Makes code reusable and clean
Modules	Keeps big programs organized

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14. Next Steps

🎯 Practice simple scripts like:

• Checking even or odd numbers
• Printing multiplication tables
• Creating your own module with a few helper functions

💡 Modify examples to include:

• break and continue
• Nested conditions
• Return values in functions