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* Lesson 05: Random numbers

** Getting set up

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[[file:images/lesson01-ticblank.png]]

You can either edit over your existing code, or start a new program.
If you want to start a new program, press *ESCAPE* until you get to
the main prompt:

Then type in =new lua=, hit *ENTER*, then =save GAMENAME.LUA=, hit
*ENTER*. (Replace "GAMENAME" with whatever you want.)

#+BEGIN_SRC terminal
  > new lua
  new cart has been created

  > save GAMENAME.lua
  cart GAMENAME.lua saved!
#+END_SRC

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--

** Draw two sprites

From this screen, press the *F2* key on the keyboard. This will take
you to the sprite editor.

Draw two sprites to use.

[[file:images/lesson-random-sprites.png]]

** Editing the code

Press the *F1* key to go to the code editor. If you started a new
project, it's going to have that starter code again. You can erase
it and replace it with this instead:

#+BEGIN_SRC lua
  -- Game setup
  x1 = math.random(0, 232)
  y1 = math.random(0, 128)

  x2 = math.random(0, 232)
  y2 = math.random(0, 128)

  rand1 = math.random(0,100)
  rand2 = 0

  -- Game loop
  function TIC()

  end
#+END_SRC

Here we are creating *six variables*. =x1= and =y1= are for one
sprite's coordinate, =x2= and =y2= are for another sprite's
coordinate, and we will also generate a couple of random numbers
=rand1= and =rand2=.

Anything we set in the "-- Game setup" area only gets set *once*. If
we do any actions within the "-- Game loop" (the =function TIC)=
area), it will be executed over and over every game loop.

Within the TIC() function, we'll add this:

#+BEGIN_SRC lua
  function TIC()
    rand2 = math.random(0, 100)
  end
#+END_SRC

So one random number is set /before/ the game loop, and the other is
set /inside/ the game loop. Now let's draw our sprites and text to
the screen.

This will also go within the TIC() function, after our =rand2=
assignment:

#+BEGIN_SRC lua
  cls(6)
  spr(0, x1, y1)
  spr(1, x2, y2)
  print(rand1, 120, 80)
  print(rand2, 120, 80)
#+END_SRC

** Testing

Now you can hit *CTRL+R* to run the program. Each time you press
*CTRL+R* the game will restart, and each item will get a new random
value. The /second/ number, however, will continually change. This
is because it is being updated /inside/ the TIC() function, so it
gets a new value each game cycle.

[[file:images/lesson-random-animation.gif]]

** Functions
  - =math.random(MIN, MAX)=

    With the random number function, you can give it a minimum
    number and a maximum number. These have to be whole numbers, but
    it can be positive, negative, or 0.

** Save your work

Make sure to press the *CTRL+S* key, or press *ESC* to go to the
prompt and type =save= to save your work! If you want to access the
folder with your code, type =folder=.

If you have a USB flash drive, make sure to copy your file over so
you don't lose it when the computer resets!

** Back to the course page!

[[../index.org][⬅️ Once you're all done, go back to the course homepage!]]