Control Flow

If Statements

If statements allow your program to make decisions based on conditions.

# Basic if statement
age = 18
if age >= 18:
    print("You are an adult")

# If-else statement
temperature = 25
if temperature > 30:
    print("It's hot outside")
else:
    print("It's not too hot")

# If-elif-else statement
score = 85
if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
elif score >= 70:
    grade = "C"
else:
    grade = "F"
print(f"Your grade is: {grade}")

Comparison Operators

# Comparison operators
x = 10
y = 5

print(x == y)    # Equal to: False
print(x != y)    # Not equal to: True
print(x > y)     # Greater than: True
print(x < y)     # Less than: False
print(x >= y)    # Greater than or equal: True
print(x <= y)    # Less than or equal: False

# String comparisons
name1 = "Alice"
name2 = "Bob"
print(name1 == name2)  # False
print(name1 < name2)   # True (alphabetical order)

Logical Operators

# and, or, not operators
has_ticket = True
has_id = True
age = 20

# and operator (both conditions must be True)
can_enter = has_ticket and has_id and age >= 18
print(can_enter)  # True

# or operator (at least one condition must be True)
is_weekend = True
is_holiday = False
can_sleep_in = is_weekend or is_holiday
print(can_sleep_in)  # True

# not operator (reverses the boolean value)
is_working_day = not (is_weekend or is_holiday)
print(is_working_day)  # False

For Loops

For loops iterate over sequences like lists, strings, or ranges.

# Loop through a list
fruits = ["apple", "banana", "orange"]
for fruit in fruits:
    print(f"I like {fruit}")

# Loop through a string
word = "Python"
for letter in word:
    print(letter)

# Loop with range()
for i in range(5):          # 0, 1, 2, 3, 4
    print(f"Count: {i}")

for i in range(1, 6):       # 1, 2, 3, 4, 5
    print(f"Number: {i}")

for i in range(0, 10, 2):   # 0, 2, 4, 6, 8
    print(f"Even: {i}")

# Loop with enumerate() to get index and value
colors = ["red", "green", "blue"]
for index, color in enumerate(colors):
    print(f"{index}: {color}")

While Loops

While loops continue as long as a condition is True.

# Basic while loop
count = 0
while count < 5:
    print(f"Count is: {count}")
    count += 1  # Same as count = count + 1

# User input loop
user_input = ""
while user_input != "quit":
    user_input = input("Enter 'quit' to exit: ")
    if user_input != "quit":
        print(f"You entered: {user_input}")

# Infinite loop with break
while True:
    number = int(input("Enter a positive number (0 to quit): "))
    if number == 0:
        break
    if number > 0:
        print(f"Square of {number} is {number**2}")
    else:
        print("Please enter a positive number")

Loop Control: break and continue

# break - exits the loop completely
for i in range(10):
    if i == 5:
        break
    print(i)  # Prints 0, 1, 2, 3, 4

# continue - skips the rest of current iteration
for i in range(10):
    if i % 2 == 0:  # Skip even numbers
        continue
    print(i)  # Prints 1, 3, 5, 7, 9

# Using break and continue together
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
for num in numbers:
    if num > 7:
        break
    if num % 2 == 0:
        continue
    print(f"Odd number: {num}")  # Prints 1, 3, 5, 7

Nested Loops

# Nested for loops
for i in range(3):
    for j in range(3):
        print(f"({i}, {j})")

# Multiplication table
for i in range(1, 4):
    for j in range(1, 4):
        result = i * j
        print(f"{i} x {j} = {result}")
    print()  # Empty line after each row

# Pattern printing
for i in range(5):
    for j in range(i + 1):
        print("*", end="")
    print()  # New line after each row
# Output:
# *
# **
# ***
# ****
# *****