Lesson 04 · Conditions¶

The if statement¶

if lets you run code only when a condition is true:

temperature = 35

if temperature > 30:
    print("It's hot outside!")

Output:

It's hot outside!

If temperature were 20, nothing would be displayed.

if True:
    print("This line is inside the if")
print("This line always runs")

if / else¶

age = 16

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

else runs when the if condition is false.

if / elif / else¶

elif (short for "else if") checks a new condition if the previous one was false:

grade = 8.5

if grade >= 9.5:
    print("Excellent — rating: Outstanding")
elif grade >= 8.5:
    print("Great — rating: Very good")
elif grade >= 7:
    print("Satisfactory — rating: Good")
elif grade >= 5:
    print("Rating: Sufficient")
else:
    print("Rating: Insufficient")

Python checks the conditions top to bottom and stops at the first true one.

Comparison operators¶

x = 5      # assignment
x == 5     # comparison → True

Logical operators¶

and — both conditions must be true¶

age = 16
has_license = False

if age >= 18 and has_license:
    print("Can drive.")
else:
    print("Cannot drive.")

or — at least one must be true¶

is_weekend = True
is_holiday = False

if is_weekend or is_holiday:
    print("No school!")

not — negates the condition¶

is_raining = False

if not is_raining:
    print("We can go outside.")

Nested conditions¶

You can place an if inside another if:

score = 85
level = "advanced"

if score >= 50:
    print("You passed the test.")
    if level == "advanced":
        print("You earned the advanced certificate!")
    else:
        print("You earned the basic certificate.")
else:
    print("You did not pass the test.")

Exercises¶

Exercise 1 — Positive, negative, or zero?¶

Ask for a number and display whether it's positive, negative, or zero.

number = float(input("Enter a number: "))
if number > 0:
    print("Positive")
elif number < 0:
    print("Negative")
else:
    print("Zero")

Exercise 2 — The largest¶

Ask for two numbers and display the larger one.

a = float(input("First number: "))
b = float(input("Second number: "))
if a > b:
    print(f"The largest is {a}")
elif b > a:
    print(f"The largest is {b}")
else:
    print("The numbers are equal")

Exercise 3 — Divisible?¶

Ask for a number and check whether it is divisible by both 3 and 5.

n = int(input("Number: "))
if n % 3 == 0 and n % 5 == 0:
    print(f"{n} is divisible by 3 and 5")
else:
    print(f"{n} is not divisible by both")

Mini-project: Grade classifier¶

Ask for a grade (1–10) and display the rating with a motivational message.

Example:

Your grade: 9.2
Rating: Very good
Congratulations! You're close to perfection!

grade = float(input("Your grade: "))

if grade < 1 or grade > 10:
    print("Invalid grade. Enter a value between 1 and 10.")
elif grade >= 9.5:
    print("Rating: Outstanding")
    print("Extraordinary! Top performance!")
elif grade >= 8.5:
    print("Rating: Very good")
    print("Congratulations! You're close to perfection!")
elif grade >= 7:
    print("Rating: Good")
    print("Good result! Keep practicing.")
elif grade >= 5:
    print("Rating: Sufficient")
    print("You passed, but you have potential for more.")
else:
    print("Rating: Insufficient")
    print("Don't lose heart! Review the material and try again.")

Summary¶

• if condition: — run a block if the condition is true
• elif other_condition: — check another condition if the previous one is false
• else: — runs when no previous condition was true
• Comparison operators: ==, !=, <, >, <=, >=
• Logical operators: and, or, not
• Indentation (4 spaces) is mandatory!

Next step: → Lesson 05: Loops