First game

Let's learn about a few new functions and then we'll be able to write our first game!

Reading input

Not only can our program print out data, but using the function io.read it can take data too. This function doesn't need any arguments because it will prompt us in the window on the right for us to type in data.

print("Enter your name:")
name = io.read()

print("Your name is " .. name .. ".")

After you click "Run", the program will pause when it runs io.read(). Type your name and hit ENTER and look, the program prints back out the name you gave it. Notice the last print statement. We combined the name with two other strings to form a sentence. You can prompt the user multiple times if you need to get additional information:

print("Enter your name:")
name = io.read()

print("What's your favorite food?")
food = io.read()

print("Your name is " .. name .. " and your favorite food is " .. food .. ".")

One limitation with doing this is the data will always come in as a string:

print("What's your favorite number?")
data = io.read()

print(type(data))

string

In the last section we talked about converting data between different types. If we wanted to find out whether your favorite number is odd or even, we would need to convert it to an actual number to perform operations on it. Type this in your text editor and run it:

print("What's your favorite number?")
data = io.read()
number = tonumber(data)

-- If the user gave us an answer that isn't a
-- number, then the value of "number" is nil.
if number == nil then
  print("Invalid number.")
elseif number % 2 == 0 then
  print("Your number is even.")
else
  print("Your number is odd.")
end

Random number

Many languages give us access to a random number generator. Randomness is how we generate secure passwords and keys in the real world. To generate a random number in Lua, we use math.random:

math.random(100)

=> 63

This generates a random number between 1 and 100. Except, if you run the program repeatedly you may notice that it spits out the same number. That's because nothing in the computer world is random. If we fed in random noises through a speaker or white noise from an old television set then our computer could use this to generate random numbers. Since we don't easily have access to those things, we need to seed Lua with some perceived randomness.

If we run os.time we will get the computer's current time in integer form:

os.time()

=> 1.529098167e+09

This number is hard enough to guess that it will work as a seed for our program. Let's take the system time and feed it in using math.randomseed then from there, Lua will be able to generate a "random" number in the range we want (1-100).

seed_number = os.time()
math.randomseed(seed_number)
print(math.random(100))

=> 19

Success! It is generated different numbers each time we run it, with no pattern.

Putting it all together

I should probably explain what this game is. It's quite simple. We want the computer to make up a number and the user has to guess what the number is. If they're wrong, then we should give them a hint and make them guess again. We can take advantage of the while loop to make them continue guessing while their guess is incorrect.

-- The computer's secret number
math.randomseed(os.time())
number = math.random(100)

print("Guess my secret number. It is between 1 and 100.")

guess = tonumber(io.read())

-- While the user's guess is not equal to
-- the number, repeat the body of the loop.
while guess ~= number do
  -- Give them some hints
  if guess > number then
    print("Your guess is too high.")
  end
  if guess < number then
    print("Your guess is too low.")
  end

  -- Make them guess again and again until they get it
  print("Guess again:")
  guess = tonumber(io.read())
end

-- Winning message
print("You guessed correctly! The number was " .. number .. ".")

Let's re-factor one bit of this code to make it easier to read. When we talked about if statements, remember the keyword else?

-- The computer's secret number
math.randomseed(os.time())
number = math.random(100)

print("Guess my secret number. It is between 1 and 100.")

guess = tonumber(io.read())

-- While the user's guess is not equal to
-- the number, repeat the body of the loop.
while guess ~= number do
  -- Give them some hints
  if guess > number then
    print("Your guess is too high.")
  else
    print("Your guess is too low.")
  end

  -- Make them guess again and again until they get it
  print("Guess again:")
  guess = tonumber(io.read())
end

-- Winning message
print("You guessed correctly! The number was " .. number .. ".")

Now that things are cleaner, let's add one feature to our program. It would be more fun if the game kept track of how many guesses we made so we could give them a special message. Let's create a variable called guess_count that will start at 1 and increment every time the user makes another guess. We'll also go ahead and add some messages to the bottom to praise the user if they did it in a reasonable number of guesses.

-- The computer's secret number
math.randomseed(os.time())
number = math.random(100)
-- Our starting number of guesses
guess_counter = 1

print("Guess my secret number. It is between 1 and 100.")

guess = tonumber(io.read())

-- While the user's guess is not equal to
-- the number, repeat the body of the loop.
while guess ~= number do
  -- Increment the guess counter by 1
  guess_counter = guess_counter + 1

  -- Give them some hints
  if guess > number then
    print("Your guess is too high.")
  else
    print("Your guess is too low.")
  end

  -- Make them guess again and again until they get it
  print("Guess again:")
  guess = tonumber(io.read())
end

-- Winning messages
print("You guessed correctly! The number was " .. number .. ".")

if guess_counter <= 5 then
  print("Amazing! It only took you " .. guess_counter .. " tries.")
else
  print("It took you " .. guess_counter .. " tries. Not bad.")
end

Exercises

• Try adding more messages for different numbers of guesses. You can modify the if statement where guess_counter is checked.
• Make the while condition exit if guess_counter goes above 10 and tell the user they lost the game (but that should try again).
• Try adding some messages to the if statement with the hints for when the user guesses an invalid number too far out of range. What if they guess a number that is more than 100? How would you do that?