Apr 2, 2026

Making Decisions with if

Last time you learned to ask yes/no questions. Today your program acts on the answers. if is how a program chooses what to do — the single idea that turns a list of steps into something that feels smart. (You saw if with the turtle in Phase I; here it really comes alive with text and input.)

The shape of a decision

if some_question_is_true:
    # do this
else:
    # otherwise do this

The test goes after if, ending with a colon. The indented lines run only when the test is True; the else lines run when it’s False.

Your code — edit it, then press Run

age = 15
if age >= 13:
  print("You're a teenager!")
else:
  print("Not a teenager yet.")

Try it 🎯

Change age to 9 and Run. Different branch!
Change the cutoff >= 13 to >= 16.

Deciding from the user’s answer

Combine if with input. Remember to convert to a number with int when comparing numbers:

Your code — edit it, then press Run

age = int(input("How old are you? "))
if age >= 18:
  print("You can vote!")
else:
  print("Not old enough to vote yet.")

More than two paths: elif

For several options, add elif (“else if”) branches. Python checks them top to bottom and runs the first one that’s True:

Your code — edit it, then press Run

score = int(input("Your test score (0-100): "))
if score >= 90:
  print("Grade: A")
elif score >= 80:
  print("Grade: B")
elif score >= 70:
  print("Grade: C")
else:
  print("Keep practicing!")

Order matters: a score of 95 matches the very first test and stops there.

Checking words

Tests can compare strings. Use .lower() so capitals don’t matter:

Your code — edit it, then press Run

answer = input("Do you like pizza? (yes/no) ")
if answer.lower() == "yes":
  print("Great taste!")
else:
  print("More for everyone else, then.")

Try it 🎯

Add an elif for the answer "maybe".

Predict it 🔮

A score of 85 runs which branch? Trace it top to bottom before you Run:

Your code — edit it, then press Run

score = 85
if score >= 90:
  print("A")
elif score >= 80:
  print("B")
else:
  print("C")

(It prints B. The first test (>= 90) is False, the second (>= 80) is True, so it runs that branch and skips the rest.)

Fix the bug 🐞

This should say “Pass” for 50 or more, but everyone gets “Fail.” Look closely at the comparison direction:

Your code — edit it, then press Run

score = int(input("Score: "))
if score < 50:
  print("Pass")
else:
  print("Fail")

(The test is backwards. To pass with 50+, use if score >= 50:.)

Your mission 🚀

Write a “weather advisor”: ask the temperature (a number), then print advice — a coat below 10, a jacket from 10 to 20, and “T-shirt weather!” above 20. Use if, elif, and else:

Your code — edit it, then press Run

temp = int(input("Temperature in degrees? "))
# if below 10 -> coat; elif 20 or below -> jacket; else -> T-shirt

What you learned today

if runs code only when a test is True; else covers the other case.
elif adds more paths; Python runs the first matching one.
Convert input with int(...) for number tests; use .lower() for word tests.
Indentation marks what belongs to each branch.

Next time is a project: you’ll combine input, if, and a score variable to build a real quiz game. 🎮

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