Lesson 3 – If Statements (Making Decisions)

In this lesson you will:

• Explain what an if statement does.
• Use comparison operators (==, !=, <, >, <=, >=).
• Write simple if and if…else statements with correct indentation.
• Use elif for more than two choices (optional/extension).
• Read and predict simple decision-making programs.

By the end you should be able to:

• Explain what an if statement does.
• Use comparison operators (==, !=, <, >, <=, >=).
• Write simple if and if…else statements with correct indentation.
• Use elif for more than two choices (optional/extension).
• Read and predict simple decision-making programs.

1. Quick recap

From Lesson 2, remember:

• Variables store values.
• We can read input using input() and convert to int or float.
• We can do basic arithmetic.

2. What is an if statement?

An if statement lets Python choose whether to run a block of code.

How it works:

• Python checks a condition.
• If the condition is True → run the indented block.
• If the condition is False → skip the block.

Example 1 – Simple if

age = int(input("Age: "))

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

Key idea: If age is 18 or more, the message prints; otherwise nothing happens.

Try it yourself

Run it several times with ages below and above 18. What happens if you type 18? What about 17?

age = int(input("Age: "))

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

3. Comparison operators

Comparison operators let you form conditions. Each comparison gives either True or False.

Example 2 – Check a password (very simple)

password = input("Enter password: ")

if password == "python123":
    print("Access granted")

Try it yourself

Run it and try typing the correct password and an incorrect one. Then change the password in the code to something else.

password = input("Enter password: ")

if password == "mypassword":
    print("Access granted")
    print("Welcome!")

4. Indentation and blocks

Important rules:

• The line after if ends with a colon :.
• The code that belongs to the if is indented (4 spaces or one Tab).
• All lines with the same indentation are part of the same block.

Example 3 – Indentation matters

score = int(input("Score: "))

if score > 50:
    print("Well done!")
    print("You passed!")
print("This line always runs.")

What happens:

• If score > 50 → both "Well done!" and "You passed!" print, then the last line.
• If not → only the last line prints.

Try it yourself

Change the score threshold (50) to a different number, or change the comparison operator (e.g., from > to < or >=). Predict what will happen, then run it.

score = int(input("Score: "))

if score > 50:
    print("Well done!")
print("You passed!")  # Not indented - always runs
print("This line always runs.")

5. if…else – two-way choice

if chooses one branch for True. else lets you say what happens when the condition is False.

Example 4 – Pass/fail

score = int(input("Score: "))

if score >= 50:
    print("You passed!")
else:
    print("You failed.")

Try it yourself

Change the pass mark to 60. Try different scores and predict the output before running.

score = int(input("Score: "))

if score >= 60:
    print("You passed!")
else:
    print("You failed.")

Example 5 – Even or odd

This uses % (modulus) from Lesson 2.

number = int(input("Enter a number: "))

if number % 2 == 0:
    print("Even")
else:
    print("Odd")

Why does number % 2 == 0 mean the number is even?

The modulus operator % gives you the remainder after division. When you divide any number by 2:

• If the remainder is 0 → the number is even (divisible by 2).
• If the remainder is 1 → the number is odd (not divisible by 2).

Examples:

• 0 % 2 = 0 → Even (0 ÷ 2 = 0 with remainder 0)
• 2 % 2 = 0 → Even (2 ÷ 2 = 1 with remainder 0)
• 4 % 2 = 0 → Even (4 ÷ 2 = 2 with remainder 0)
• 10 % 2 = 0 → Even (10 ÷ 2 = 5 with remainder 0)
• 3 % 2 = 1 → Odd (3 ÷ 2 = 1 with remainder 1)
• 7 % 2 = 1 → Odd (7 ÷ 2 = 3 with remainder 1)

Try it yourself

Test several numbers: 0, 1, 2, 7, 10. Predict if each is "Even" or "Odd" before running.

number = int(input("Enter a number: "))

if number % 2 == 0:
    print("Even")
    print("The number is divisible by 2")
else:
    print("Odd")
    print("The number is not divisible by 2")

6. elif – more than two choices

Use elif ("else if") for 3+ options.

Example 6 – Grade bands

score = int(input("Score: "))

if score >= 80:
    print("Grade A")
elif score >= 60:
    print("Grade B")
elif score >= 40:
    print("Grade C")
else:
    print("Grade D")

Try it yourself

Change the score boundaries or add another grade. Try scores like 39, 40, 59, 60, 79, 80.

score = int(input("Score: "))

if score >= 90:
    print("Grade A*")
elif score >= 80:
    print("Grade A")
elif score >= 60:
    print("Grade B")
elif score >= 40:
    print("Grade C")
else:
    print("Grade D")

9. Understanding Quiz

Answer all questions below, then click "Check Answers" at the end to see your score.

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

age = int(input("Age: "))

if age < 13:
    print("Child ticket")
else:
    print("Full price")

score = int(input("Score: "))

if score >= 80:
    print("Grade A")
elif score >= 60:
    print("Grade B")
elif score >= 40:
    print("Grade C")
else:
    print("Grade D")

num = int(input("Number: "))

if num > 5:
    print("Big")
else:
    print("Small")

score = int(input("Score: "))

if score > 50:
    print("Pass")
elif score >= 50:
    print("Borderline")
else:
    print("Fail")

x = int(input("x: "))

if x % 2 == 0:
    print("Even")
if x > 5:
    print("Big")
else:
    print("Small")

n = int(input("n: "))

if n >= 5:
    print("A")
    if n == 5:
        print("B")
else:
    print("C")
print("Done")

8. Coding tasks – If statements practice

Complete all the tasks below. Do one task at a time, run your code, and check the output.

• Task 1 – Temperature checker
  Write a program that:
  • Asks for temp (integer).
  • If temp >= 20, prints Nice and warm.
  • Else prints A bit cold.
• Task 2 – Login check
  Write a program that:
  • Asks for username (string).
  • If username == "admin", prints Welcome, admin.
  • Else prints Access denied.
• Task 3 – Exam result
  Write a program that:
  • Asks for mark out of 100 (integer).
  • If mark >= 80, prints Distinction.
  • Elif mark >= 50, prints Pass.
  • Else prints Fail.
• Task 4 – Bus fare
  Write a program that:
  • Asks for age (integer).
  • If age < 11, prints Free travel.
  • Elif age <= 18, prints Child fare.
  • Else prints Adult fare.
• Task 5 – Password length checker
  Write a program that:
  • Asks for password (string).
  • If the password has 8 or more characters, prints Strong enough.
  • Else prints Too short.

  Hint: len(password) says how many characters were typed.

• Task 6 – Even or odd
  Write a program that:
  • Asks for number (integer).
  • If the number is even, prints Even.
  • Else prints Odd.
• Task 7 – Times table checker
  Write a program that:
  • Asks for number (integer).
  • If the number is in the 5 times table (divisible by 5), prints In the 5 times table.
  • Else prints Not in the 5 times table.
• Task 8 – Guess the number
  Write a program that:
  • Sets secret = 7.
  • Asks the user for a guess (integer).
  • If the guess is correct, prints Correct!.
  • Else prints Wrong!.

Answer all the above tasks here

Use the editor below to complete the coding tasks above.