# While loop example - condition-based repetition
count = 1
while count <= 5:
    print(f"Count: {count}")
    count += 1

print("While loop finished!")

# For loop example - iteration over a sequence
fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(f"I like {fruit}")

print("For loop finished!")

# For loop with range - number sequences
for number in range(1, 6):
    print(f"Number: {number}")

# Comparison: doing the same task with both loops
print("\n=== Counting with while loop ===")
i = 1
while i <= 3:
    print(f"While: {i}")
    i += 1

print("\n=== Counting with for loop ===")
for i in range(1, 4):
    print(f"For: {i}")

# When to use which loop:
# Use WHILE when you don&apos;t know how many iterations you need
# Use FOR when you know the sequence or collection to iterate over

# break statement - exit the loop immediately
print("=== Break Example ===")
for number in range(1, 10):
    if number == 5:
        print("Found 5! Breaking out of loop.")
        break
    print(f"Number: {number}")
print("Loop ended")

# continue statement - skip to the next iteration
print("\n=== Continue Example ===")
for number in range(1, 8):
    if number % 2 == 0:  # Skip even numbers
        continue
    print(f"Odd number: {number}")

# Using break and continue together
print("\n=== Finding First Even Number ===")
numbers = [1, 3, 7, 4, 9, 6, 2]
for num in numbers:
    if num % 2 != 0:  # If odd, skip it
        continue
    print(f"First even number found: {num}")
    break
else:
    print("No even number found")

# pass statement - placeholder (does nothing)
print("\n=== Pass Statement ===")
for i in range(3):
    if i == 1:
        pass  # Placeholder - do nothing for now
    else:
        print(f"Processing: {i}")

# Practical example: validating user input
print("\n=== Input Validation with Loops ===")
valid_choices = ["yes", "no", "maybe"]
user_input = ""

# Note: In real code, you'd use input() here
# This is just for demonstration
sample_inputs = ["invalid", "also invalid", "yes"]

for sample in sample_inputs:
    print(f"User entered: {sample}")
    if sample.lower() in valid_choices:
        user_input = sample
        print(f"Valid choice: {user_input}")
        break
    else:
        print("Invalid choice, please try again.")
else:
    print("No valid input provided")

# Pattern 1: Accumulator - building up a result
total = 0
numbers = [10, 20, 30, 40, 50]
for num in numbers:
    total += num
print(f"Sum: {total}")

# Pattern 2: Counter - counting items that meet criteria
even_count = 0
for num in range(1, 11):
    if num % 2 == 0:
        even_count += 1
print(f"Even numbers: {even_count}")

# Pattern 3: Finder - searching for specific items
names = ["Alice", "Bob", "Charlie", "Diana"]
search_name = "Charlie"
found = False

for name in names:
    if name == search_name:
        print(f"Found {search_name}!")
        found = True
        break

if not found:
    print(f"{search_name} not found")

# Pattern 4: Transformer - modifying elements
original_prices = [10.99, 25.50, 8.75, 15.00]
discounted_prices = []

for price in original_prices:
    discounted_price = price * 0.9  # 10% discount
    discounted_prices.append(discounted_price)

print(f"Original: {original_prices}")
print(f"Discounted: {discounted_prices}")

# Pattern 5: Filter - selecting items that meet criteria
scores = [85, 92, 78, 96, 88, 74, 90]
passing_scores = []

for score in scores:
    if score >= 80:
        passing_scores.append(score)

print(f"Passing scores: {passing_scores}")

# Pattern 6: Validator - checking all items
valid_emails = True
email_list = ["user@example.com", "admin@site.org", "invalid-email"]

for email in email_list:
    if "@" not in email or "." not in email:
        print(f"Invalid email: {email}")
        valid_emails = False

if valid_emails:
    print("All emails are valid")
else:
    print("Some emails are invalid")

# Pattern 7: Menu loop - repeat until user chooses to exit
choices = ["1", "2", "3", "4"]
print("\n=== Menu Loop Pattern ===")
for choice in ["1", "2", "invalid", "4"]:  # Simulating user input
    print(f"User chose: {choice}")
    
    if choice == "1":
        print("Processing option 1...")
    elif choice == "2":
        print("Processing option 2...")
    elif choice == "3":
        print("Processing option 3...")
    elif choice == "4":
        print("Exiting...")
        break
    else:
        print("Invalid choice, please try again")

# Pattern 8: Data processing pipeline
raw_data = ["  Alice  ", "BOB", "charlie", "  DIANA "]
processed_names = []

for raw_name in raw_data:
    # Clean and format the name
    clean_name = raw_name.strip().title()
    processed_names.append(clean_name)

print(f"Processed names: {processed_names}")

# Basic nested loop structure
print("=== Basic Nested Loops ===")
for i in range(1, 4):
    print(f"Outer loop: {i}")
    for j in range(1, 3):
        print(f"  Inner loop: {j}")
    print()  # Empty line for clarity

# Multiplication table
print("=== Multiplication Table ===")
for i in range(1, 6):
    for j in range(1, 6):
        product = i * j
        print(f"{product:2}", end=" ")
    print()  # New line after each row

# Processing 2D data structure
print("\n=== Processing 2D Data ===")
matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
]

# Find sum of all elements
total = 0
for row in matrix:
    for element in row:
        total += element
print(f"Sum of all elements: {total}")

# Find maximum element
max_element = matrix[0][0]  # Start with first element
for row in matrix:
    for element in row:
        if element > max_element:
            max_element = element
print(f"Maximum element: {max_element}")

# Creating patterns with nested loops
print("\n=== Star Patterns ===")

# Right triangle pattern
for i in range(1, 6):
    for j in range(i):
        print("*", end="")
    print()

print()  # Separator

# Rectangle pattern
for i in range(4):
    for j in range(6):
        print("*", end="")
    print()

print()  # Separator

# Number pattern
for i in range(1, 5):
    for j in range(1, i + 1):
        print(j, end="")
    print()

# Real-world example: Student grade processing
print("\n=== Student Grade Processing ===")
students = {
    "Alice": [85, 92, 78, 96],
    "Bob": [88, 84, 90, 87],
    "Charlie": [92, 89, 94, 91]
}

for student_name, grades in students.items():
    total_points = 0
    for grade in grades:
        total_points += grade
    
    average = total_points / len(grades)
    print(f"{student_name}: Average = {average:.1f}")

# Searching in 2D structure
print("\n=== Finding Item in 2D List ===")
classroom = [
    ["Alice", "Bob", "Charlie"],
    ["Diana", "Eve", "Frank"],
    ["Grace", "Henry", "Iris"]
]

search_student = "Eve"
found_position = None

for row_index, row in enumerate(classroom):
    for col_index, student in enumerate(row):
        if student == search_student:
            found_position = (row_index, col_index)
            break
    if found_position:
        break

if found_position:
    print(f"{search_student} found at row {found_position[0]}, column {found_position[1]}")
else:
    print(f"{search_student} not found")

# Nested loop with conditions and breaks
print("\n=== Complex Nested Loop Example ===")
numbers = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
target = 5

for i, row in enumerate(numbers):
    for j, num in enumerate(row):
        if num == target:
            print(f"Found {target} at position ({i}, {j})")
            break
    else:
        continue  # Continue outer loop if inner loop completed normally
    break  # Break outer loop if inner loop was broken

# Best Practice 1: Descriptive variable names
# Bad
for i in ["apple", "banana", "cherry"]:
    print(i)

# Good
for fruit in ["apple", "banana", "cherry"]:
    print(fruit)

# Best Practice 2: Use enumerate() for index access
# Bad
fruits = ["apple", "banana", "cherry"]
index = 0
for fruit in fruits:
    print(f"{index}: {fruit}")
    index += 1

# Good
for index, fruit in enumerate(fruits):
    print(f"{index}: {fruit}")

# Best Practice 3: Avoid manual index management
# Bad
items = ["a", "b", "c", "d"]
i = 0
while i < len(items):
    print(items[i])
    i += 1

# Good
for item in items:
    print(item)

# Best Practice 4: Use zip() for parallel iteration
# Bad
names = ["Alice", "Bob", "Charlie"]
scores = [85, 92, 78]
for i in range(len(names)):
    print(f"{names[i]}: {scores[i]}")

# Good
for name, score in zip(names, scores):
    print(f"{name}: {score}")

# Best Practice 5: Extract complex logic into functions
def process_student_data(student_name, grades):
    """Process individual student data."""
    if not grades:
        return f"{student_name}: No grades available"
    
    average = sum(grades) / len(grades)
    letter_grade = "A" if average >= 90 else "B" if average >= 80 else "C"
    return f"{student_name}: {average:.1f} ({letter_grade})"

# Clean loop using the helper function
students_data = {
    "Alice": [85, 92, 78, 96],
    "Bob": [88, 84, 90, 87],
    "Charlie": []
}

for student, grades in students_data.items():
    result = process_student_data(student, grades)
    print(result)

# Best Practice 6: Use list comprehensions when appropriate
# Traditional loop
squared_numbers = []
for num in range(1, 6):
    squared_numbers.append(num ** 2)

# List comprehension (more Pythonic)
squared_numbers = [num ** 2 for num in range(1, 6)]
print(f"Squared numbers: {squared_numbers}")

# Best Practice 7: Handle edge cases
def safe_division(numbers, divisor):
    """Safely divide a list of numbers."""
    if divisor == 0:
        return "Cannot divide by zero"
    
    results = []
    for num in numbers:
        results.append(num / divisor)
    return results

numbers = [10, 20, 30]
print(f"Division results: {safe_division(numbers, 2)}")
print(f"Division by zero: {safe_division(numbers, 0)}")

# Best Practice 8: Use break and continue wisely
def find_first_positive(numbers):
    """Find the first positive number in a list."""
    for num in numbers:
        if num <= 0:
            continue  # Skip non-positive numbers
        return num  # Return immediately when found
    return None  # No positive number found

test_numbers = [-5, -2, 0, 3, 7]
result = find_first_positive(test_numbers)
print(f"First positive number: {result}")

# Best Practice 9: Avoid modifying lists while iterating
# Bad - can cause issues
items = [1, 2, 3, 4, 5]
# Don&apos;t do this: for item in items: items.remove(item)

# Good - iterate over a copy or use list comprehension
items = [1, 2, 3, 4, 5]
items = [item for item in items if item % 2 == 0]  # Keep even numbers
print(f"Even items: {items}")

# Best Practice 10: Use appropriate data structures
# If you need to check membership frequently, use a set
valid_codes = {"ABC", "DEF", "GHI", "JKL"}  # Set for fast lookup
input_codes = ["ABC", "XYZ", "DEF", "QRS"]

for code in input_codes:
    if code in valid_codes:  # Fast O(1) lookup
        print(f"{code}: Valid")
    else:
        print(f"{code}: Invalid")