03 - Mastering Control Flow (Loops & Conditionals) in Python

• python
• by Sn0wAlice

Introduction

Control flow allows your program to make decisions and execute code conditionally or repeatedly. This step will guide you through if-else statements, loops (for, while), and loop control statements.

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1. Conditional Statements (if-elif-else)

Conditional statements allow the program to make decisions based on conditions.

Basic if Statement

age = 18
if age >= 18:
    print("You are an adult.")

if-else Statement

num = 10
if num % 2 == 0:
    print("Even number")
else:
    print("Odd number")

if-elif-else (Multiple Conditions)

score = 85
if score >= 90:
    print("Grade: A")
elif score >= 80:
    print("Grade: B")
elif score >= 70:
    print("Grade: C")
else:
    print("Grade: F")

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2. Loops (for & while)

Loops allow you to execute a block of code multiple times.

For Loop

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

Using range() in For Loop

for i in range(5):
    print(i)

While Loop

count = 0
while count < 5:
    print("Count:", count)
    count += 1

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3. Loop Control Statements

Break Statement (Exit Loop Early)

for i in range(10):
    if i == 5:
        break  # Stops loop when i equals 5
    print(i)

Continue Statement (Skip Current Iteration)

for i in range(5):
    if i == 2:
        continue  # Skips when i is 2
    print(i)

Pass Statement (Placeholder for Future Code)

for i in range(5):
    if i == 3:
        pass  # Placeholder, does nothing
    print(i)

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4. Nested Loops & Conditionals

Loops and conditionals can be nested within each other.

Example: Nested Loops

for i in range(3):
    for j in range(2):
        print(f"i: {i}, j: {j}")

Example: Nested if Statements

num = 15
if num > 10:
    if num % 2 == 0:
        print("Even number greater than 10")
    else:
        print("Odd number greater than 10")

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Exercises

• Write a program that asks the user for a number and prints whether it is positive, negative, or zero.
• Write a loop that prints numbers from 1 to 10, but skips 5 using the continue statement.
• Write a program that prints the first 10 even numbers using a while loop.
• Create a nested loop that prints a multiplication table (1-5).
• Write a program that categorizes a given number based on multiple conditions using if-elif-else.

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Conclusion

You have now mastered control flow in Python, including conditionals, loops, and loop control statements. The next step is to dive into functions and modular programming.

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