If statements

What are if statements?

If statements let your program make decisions. They check if something is true or false, then act accordingly. Real-life logic:

IF it’s raining THEN take umbrella
IF battery < 20% THEN charge phone
IF password correct THEN allow access

Basic if statement

age = 18

if age >= 18:
    print("You can vote!")
    print("You're an adult")

How it works:

Check the condition (age >= 18)
If True, run the indented code
If False, skip it

The colon : and indentation are required! This is how Python knows what code belongs to the if statement.

If-else statements

Handle both True and False cases:

temperature = 25

if temperature > 30:
    print("It's hot!")
else:
    print("Nice weather!")

If-elif-else chains

For multiple conditions:

score = 85

if score >= 90:
    print("A - Excellent!")
elif score >= 80:
    print("B - Good job!")
elif score >= 70:
    print("C - Keep it up!")
else:
    print("F - Need improvement")

Python checks each condition in order and runs the first True one.

Why elif instead of multiple if statements? With elif, Python stops checking once it finds a true condition. This is more efficient and prevents multiple blocks from running. The order matters - always put more specific conditions first!

Multiple conditions

Combine conditions with and, or, not:

age = 25
has_license = True

# Both must be True
if age >= 18 and has_license:
    print("You can drive!")

# At least one must be True
if weekend or holiday:
    print("No work today!")

# Reverse the condition
if not raining:
    print("Let's go outside!")

Nested if statements

Put if statements inside other if statements:

has_ticket = True
age = 15

if has_ticket:
    if age >= 18:
        print("Enjoy the movie!")
    else:
        print("Need adult supervision")
else:
    print("Buy a ticket first")

Common mistakes

Forgetting the colon

# Wrong
if x > 5
    print("Big")

# Right
if x > 5:
    print("Big")

Using = instead of ==

# Wrong (assignment)
if x = 5:
    print("Five")

# Right (comparison)
if x == 5:
    print("Five")

Wrong indentation

# Wrong
if True:
print("Hello")  # IndentationError

# Right
if True:
    print("Hello")

What’s next?

Now let’s learn about loops to repeat code efficiently!

Loops

Repeat code without copying

Getting started

Data types

Working with data

Control flow

Data structures

What are if statements?

Basic if statement

If-else statements

If-elif-else chains

Multiple conditions

Nested if statements

Common mistakes

What’s next?

Loops

​What are if statements?

​Basic if statement

​If-else statements

​If-elif-else chains

​Multiple conditions

​Nested if statements

​Common mistakes

​What’s next?

Loops

What are if statements?

Basic if statement

If-else statements

If-elif-else chains

Multiple conditions

Nested if statements

Common mistakes

What’s next?