Build a Guess-the-Number Game – Loops and Randomness

Tools You’ll Use

• Python 3 (Google Colab, Jupyter Notebook, or any Python interpreter)
• Code editor/IDE (VS Code, Thonny, PyCharm, or even a text editor)
• Web browser (for documentation and debugging help)

Lesson Roadmap

1. Review loops: why repetition is important in programming.
2. Generate random numbers with Python’s random module.
3. Plan the game: input, feedback, winning condition.
4. Write the code: loop until correct.
5. Add features: attempt counter, hints, quit option.
6. Test with different runs and edge cases.
7. Recap key ideas with a quiz.
8. Mini challenge: difficulty levels & scoreboard.

Why Loops Matter

When we wrote the calculator in Lesson 2, the program ran once and ended. But in many programs, we want repetition:

• Try again until successful login.
• Keep asking until the user gives valid input.
• Run through all items in a list.

This is where loops come in. Think of loops as “automatic patience”: instead of us retyping the same code, Python runs it for us repeatedly until the job is done.

Types of Loops in Python

1. while loop → repeat as long as a condition is true.

   count = 1
   while count <= 5:
       print("Attempt:", count)
       count += 1
   

   (This runs 5 times because the condition stops when count > 5.)

2. for loop → repeat over a fixed collection (like a list or range).

   for i in range(5):
       print("Attempt:", i)
   

   (This runs 5 times automatically, from 0 to 4.)

👉 In our game, we’ll use a while loop because we don’t know in advance how many guesses the player will need.

Step 1: Random Numbers in Python

A game needs unpredictability. If the secret number were always the same, it would be boring. Python’s random module solves this:

import random
number = random.randint(1, 100)   # random number between 1 and 100
print(number)   # test: see what number is picked

Each run gives a different number. (If you keep getting the same number, check that you’re not hardcoding it.)

Step 2: Plan the Game

Game rules:

1. Computer picks a number between 1 and 100.
2. User guesses until correct.

3. After each guess:

   • Too low → tell them “Try a bigger number”.
   • Too high → tell them “Try a smaller number”.
   • Correct → congratulate them and show attempts.

Flowchart:

Pick random number → Ask for guess → Compare → Feedback
          ↑                                   ↓
          └────────── loop until correct ─────┘

Step 3: First Version of the Code

import random

secret_number = random.randint(1, 100)

print("Welcome to Guess the Number!")
print("I'm thinking of a number between 1 and 100.")

guess = None
attempts = 0

while guess != secret_number:
    guess = int(input("Enter your guess: "))
    attempts += 1

    if guess < secret_number:
        print("Too low! Try again.")
    elif guess > secret_number:
        print("Too high! Try again.")
    else:
        print(f"🎉 Congratulations! You guessed it in {attempts} tries.")

Step 4: Thinking Like a Programmer

• The variable attempts is our memory of how many guesses were made.
• The loop’s condition while guess != secret_number ensures the game keeps running until success.
• Feedback (if/elif/else) helps the user narrow down the possibilities — this is binary search thinking: cut the search space in half each time.

👉 Intuition tip: If the number is between 1 and 100, a clever player can always guess it in at most 7 tries by halving the range each time (like guessing 50 first, then 25 or 75, etc.).

Sample Runs

Example 1:

Welcome to Guess the Number!
I'm thinking of a number between 1 and 100.
Enter your guess: 50
Too high! Try again.
Enter your guess: 25
Too low! Try again.
Enter your guess: 35
🎉 Congratulations! You guessed it in 3 tries.

Example 2 (lucky guess):

Enter your guess: 72
🎉 Congratulations! You guessed it in 1 try.

Common Mistakes & Debugging Tips

• Forgetting int() conversion: input() always returns a string → if guess < secret_number will crash unless you convert it.
• Infinite loop: If you forget to update guess inside the loop, it runs forever.
• Hardcoded number: If you set secret_number = 50 for testing but forget to remove it, the game is no longer random.
• Edge case: What if the user enters text instead of a number? (The program crashes. You can fix this later with try/except.)

Debugging tip: Use print(secret_number) during testing to see the hidden answer. Remove it when finished.

Step 5: Adding Features

Let’s add more polish:

1. Limit attempts (Hard mode)

max_attempts = 5

while guess != secret_number and attempts < max_attempts:
    # guessing logic as before...

At the end, check if they ran out of attempts:

if guess != secret_number:
    print("Game over! The number was", secret_number)

2. Allow quitting

user_input = input("Enter your guess (or 'q' to quit): ")

if user_input.lower() == 'q':
    print("You gave up! The number was", secret_number)
    break

3. Smarter feedback (difference-based)

if abs(guess - secret_number) <= 5:
    print("Very close!")

Real-World Applications

This game models trial-and-error with feedback, just like in real life:

• Teachers giving hints on homework (“too big, try smaller”).
• Login systems giving limited attempts before lockout.
• Scientific experiments narrowing down hypotheses.

It shows why programming is useful: computers can patiently repeat checks thousands of times, while humans might give up.

Recap of Key Concepts

• Loops: while keeps running until the condition is false.
• Randomness: random.randint() makes programs less predictable.
• Control flow: Feedback (if/elif/else) inside loops guides user interaction.
• Counters: Track attempts to measure performance.

Review Questions

1. Why do we use a while loop instead of a for loop here?
2. What happens if you forget to increment attempts?
3. How many guesses do you need at most to find a number between 1 and 100 if you play optimally?

Mini Challenges

1. Difficulty levels

   • Easy = unlimited guesses
   • Medium = 10 guesses
   • Hard = 5 guesses (Use if statements to set max_attempts.)

2. Leaderboard Track the fewest attempts across multiple rounds.

3. Range selection Let the player choose the range (1–50, 1–500, etc.).

4. Hint system After 3 wrong guesses, give a clue: “The number is divisible by 2” or “The number is greater than 50”. *draft the worked-out code for Mini Challenge 1 (Difficulty Levels)** so your students see a full extension project, like we did with the calculator lesson’s exponentiation challenge?