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28. if Statements

1. Introduction​

The if statement is used to make decisions in Python.
It allows your program to execute certain code only if a condition is true.

2. Basic if Statement​

age = 18

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

Output:

You are an adult

3. Indentation Matters​

Python uses indentation (spaces) to define blocks of code.

❌ Wrong:

if True:
print("Hello")   # Error: expected an indented block

✅ Correct:

if True:
    print("Hello")

4. Using Comparison Operators in if​

temperature = 25

if temperature > 30:
    print("It's hot!")
if temperature < 10:
    print("It's cold!")
if temperature == 25:
    print("Perfect weather!")

5. if with Boolean Variables​

is_logged_in = True

if is_logged_in:
    print("Welcome back!")

6. if with Expressions​

Any expression that evaluates to True or False can be used:

name = "Alice"

if name:   # non-empty strings are True
    print("Name provided")

7. Nested if Statements​

You can put an if inside another if:

age = 20
has_id = True

if age >= 18:
    if has_id:
        print("Access granted")

8. Common Mistakes​

  • Forgetting the colon (:) after the condition.
  • Misusing = instead of ==:
x = 5
if x == 5:   # ✅ correct
    print("x is 5")

# if x = 5:  # ❌ invalid

9. Practical Example​

password = "python123"
user_input = "python123"

if user_input == password:
    print("Login successful")

10. Next Steps​

✅ You now know how to use if statements for decision-making.
In the next chapter, we’ll expand on this with elif and else clauses.