3: Control Flow

3.1 Conditionals: Making Decisions with if, elif, and else

In real life, you make decisions all the time: "If it’s sunny, I’ll go for a walk, if not, I’ll stay home." In programming, conditional statements do exactly that: they allow your code to make decisions based on whether a condition is true or false.

if statement

The if statement is the most basic one. It executes a block of code only if a condition is True.

age = 18

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

else statement

The else statement is used together with if to execute an alternative block of code when the if condition is False.

temperature = 15

if temperature > 25:
    print("It’s hot, wear light clothes.")
else:
    print("It’s cold, dress warmly.")

elif (else if) statement

The elif statement lets you check multiple conditions sequentially. It’s short for "else if" and helps you avoid nesting too many if statements.

score = 85

if score >= 90:
    print("You got an A, excellent!")
elif score >= 80:
    print("You got a B, well done!")
elif score >= 70:
    print("You got a C, keep practicing!")
else:
    print("You need to study more.")

3.2 Comparison and Logical Operators

To create conditions for your if statements, you need comparison operators and logical operators.

Comparison operators

They compare two values and return a boolean result (True or False).

• == Equal to
• != Not equal to
• > Greater than
• < Less than
• >= Greater than or equal to
• <= Less than or equal to

x = 10
y = 20

print(x == y)  # Output: False
print(x < y)   # Output: True
print(x != y)  # Output: True

Logical operators

They combine multiple boolean conditions.

• and: Returns True if both conditions are True.
• or: Returns True if at least one condition is True.
• not: Reverses the boolean value (from True to False and vice versa).

age = 25
has_license = True

if age >= 18 and has_license:
    print("You can drive.")

if age < 18 or not has_license:
    print("You cannot drive.")

3.3 Loops: Repeating Tasks with for and while

Loops let you run a block of code repeatedly, which is essential for automating tasks.

for loop

The for loop is used to iterate over a sequence (such as a list, tuple, dictionary, or string).

# Iterate over a list
fruits = ["apple", "banana", "grape"]
for fruit in fruits:
    print(fruit)

# Iterate with a range of numbers
for i in range(5): # range(5) generates numbers from 0 to 4
    print(i)

while loop

The while loop runs as long as a condition is True. It’s important that the condition eventually becomes False to avoid an infinite loop.

counter = 0

while counter < 5:
    print(counter)
    counter += 1 # Same as counter = counter + 1

break and continue statements

• break: Stops the loop execution and exits it completely.
• continue: Skips the current iteration and moves to the next one.

for number in range(10):
    if number == 3:
        continue # Skip 3 and continue with the next iteration
    if number == 8:
        break    # Stop the loop completely
    print(number)

This module has equipped you with the tools to make your programs dynamic, capable of making decisions and repeating actions. In the next module, you’ll discover how to organize your code into reusable blocks using functions.