THE BEGINNER'S PAGE

Richard Mansfield, Senior Editor

Writing A Simulation Game

There are three basic types of computer games: arcade, adventure, and simulation games. Let's briefly look at the characteristics of arcade and adventure games and then write a simulation.

Realtime Action

Arcade games feature what's called realtime action. Unlike chess or bridge, things happen fast. You can't sit back and plan your next move; you must react immediately to the space invaders. In other words, events take place at the same speed as they would in reality: realtime.

Arcade games also have a strong appeal to the eye and ear. There is much animation, color, and sound. In fact, your ability to respond quickly and effectively depends in part on all the clues you get from the graphics and sound effects. Strategy, while often an aspect of arcade play, is clearly secondary. These games are a new kind of athletics: the fun of man versus machine. Like auto racing, arcade games are essentially isometric exercises – you don't run around; you just stay in one place flexing and unflexing your muscles, tensing and relaxing.

Story And Strategy

Strategy, however, is more important in "adventure" games. The emphasis is on planning ahead and solving riddles. It can be like living inside an adventure novel. There is drama, characterization, and plot. You might start out, for example, in a forest with a shovel and a trusty, if enigmatic, companion parrot. As you try to figure out what to do next, the parrot keeps saying "piny dells, piny dells." After wandering aimlessly through the trees, it suddenly comes to you that the bird is saying "pine needles" and you dig through them and find a treasure map.

Your "character" will travel, meet friends and enemies, and have the opportunity to pick up or ignore potentially useful items such as food, magic wands, and medicine. It's customary that you cannot haul tons of provisions. You'd have to decide whether or not to leave the shovel in the forest. Yet you might be sorry that you'd dropped it if you're involved in a cave-in later in the game.

In any case, adventure games are fundamentally verbal. The computer displays the words:

YOU ARE IN A BOAT ON A LAKE. NIGHT IS FALLING.

to which you can respond in any number of ways. You might type:

DIVE OFF BOAT.

and the computer would reply that you now see an underwater cave or whatever. You move through the scenes the way a character moves through a novel. There is generally no penalty if you take time to plan your next move. It's not realtime.

Imitations Of Life

The third category, simulation, is the least common kind of computer game. This is because to really imitate something, to simulate it effectively, you need lots of computer memory to hold lots of variables. However, memory has recently become far less expensive so we can expect to see increasingly effective simulation games. Star Trek and Hammurabi, both simulations, have long been popular home computer games. Although they are similar to adventure games, simulations are random. That is, there is no secret to discover, no puzzle to solve, no plot. Like real life, things happen with unpredictable, complex results.

Here's a program which simulates investing. The key to simulating is to arrange realistic interactions between variables. Look at line 600. If there is "international unrest," the price of gold (PGLD) goes up and the price of Bundtfund stock (PB) goes down. This relationship between gold, stock, and an international crisis is true to life. Alternatively, stock goes up and gold goes down in line 700 during a "market rally."

The game allows you to make investment decisions, and then a "month" passes during which the value of your investments will go up or down. In line 510, three variables are given random values. Stock can gain or lose up to 10 points (variable X), and gold can change by $20 an ounce (Y). Variable Z will be used to simulate flipping a coin. Also notice lines 520 and 525. In 520, we determine whether or not there will be unrest. The variable CH is just a counter. Each "month," CH is raised by one. Two conditions are required for unrest to happen: in a given month, CH must be greater than 4 and it must be less than whatever X turns out to be. If both these conditions are met, CH is reset to zero and we've got international unrest. This has the effect of creating unrest roughly every four to six months. Likewise, another rhythm is set up in line 525 to cause market rallies. In both cases, however, you cannot be certain exactly when to invest in gold or in stocks.

The decision to raise or lower stock prices is made in line 530 and based on the coin toss variable, Z. Again, stocks move in opposition to gold. Prices will rise about 50 percent of the time, but you can never know what will happen in a given month.

Suggested Complications

This is the core, a rough sketch, of an investment simulation game. There is much you can do to make it a more effective simulation and thereby a more enjoyable game. The more variables in a simulation, the better. For example, add leverage and additional "incidents" which affect prices, improve the randomizing, and include other types of investments. You could even use a separate counter which, every five years, causes the X and Y variables to swing more widely to reflect recession/recovery cycles.

As you can see, a simulation should be lifelike. It has interdependent cycles and a degree of unpredictability. Its realism derives from including a sufficient number of variables. And those variables must interact in plausible ways and with just the right amount of randomness. A simulation is a little world you create. You can define cause and effect and then fine-tune the whole thing until it seems well-balanced. Adventure and arcade games are certainly enjoyable, but this investment simulation can be built up to the point where it's just as much fun as any other kind of game.

Mixing Styles

Of course, these three categories – arcade, adventure, and simulation – are somewhat arbitrary. Some of the best games contain elements of each. There are adventure games with graphics – you see the forest, the shovel, the pine needles. After you say DIVE, your character jumps into a lake and the screen transforms into an underwater scene. Likewise, arcade games can include the different "settings" so characteristic of adventure games. Popular arcade games such as Tron and Donkey Kong change the playfield as you earn more points.

There are several ways to add to the appeal of our investment simulation, beyond just making it a more complex, more accurate simulation. You could add the visuals and sound of arcade games. Try creating a tickertape across the top of the screen to show price changes and news events. Maybe add a bell sound to indicate the end of further transactions. If your computer has a voice synthesizer, news events could be announced over the "radio." And from adventure games you could borrow two elements: riddles and the necessity of planning ahead. One easy way to incorporate these two elements would be to make paying taxes a part of the game. After all, the closer it is to real life, the better the simulation.

Special Program Notes: If you have an Atari, you'll need to add semicolons (;) between the variable names and the PRINT statements to make everything print on a single line. If you have a TI, put each statement on its own separate line. In other words, you cannot use colons (:). Line 10 would be CASH = 100000 and you'd need to add a line: 11 PGLD = 400. If you have a Timex/ Sinclair, use LET whenever a variable is defined. For example, line 10 would start: 10 LET CASH = 100000. If you have a TRS-80 Color Computer, add the following line: 5 RANDOMIZE.

Investment Simulation

10 CASH = 100000 : PGLD = 400
20 PB = 80
31 PRINT : PRINT" BUNDTFUND IS $"PB" PER SHARE.YOU HAVE "B" SHARES. -- $"PB*B
33 PRINT" GOLD IS{3 SPACES)$"PGLD" PER OUNCE.{2 SPACES}YOU HAVE "GLD" OUNCES. -- $"GLD*PGLD
34 T = PB * B + GLD * PGLD
35 PRINT"{31 SPACES}TOTAL INVESTMENTS -- $"T
36 PRINT"{31 SPACES}YOU HAVE $"CASH" TO SPEND."
40 PRINT"{24 SPACES }GRAND TOTAL (INVESTMENTS + CASH) $"T + CASH
45 IFCK = 1THEN500
50 PRINT : PRINT"1.BUY{2 SPACES]2.SELL {2 SPACES)3.DONE"
60 INPUTA : IFA = 3THENCK = 1 : GOTO31
100 PRINT"WHICH?{3 SPACES}1.GOLD {2 SPACES}OR{2 SPACES)2.STOCK"
110 INPUTF
120 PRINT"HOW MANY (SHARES OR OUNCES)?"
130 INPUTN
140 IFF = 1THEN160
150 PRICE = PB * N : IFA = 1THENCASH = CASH-PRICE: B = B + N : GOTO400
155 CASH = CASH + PRICE:B = B - N : GOTO400
160 PRICE = PGLD * N : IFA = 1THENCASH = CASH - PRIC E : GLD = GLD + N : GOTO400170 CASH=CASH + PRICE : GLD=GLD-N
400 GOTO50
500 CK = 0 : PRINT : PRINT" ONE MONTH LATER ..
." : FORT= 1 TO 700 : NEXT T : PRINT
510 X = INT((RND(1)*100)/10):Y = INT((RND(1)
*200)/l0) : Z = RND(1)
520 CH = CH+1 : IFCH >4ANDCH < X THEN CH = 0 : GOTO60
0
525 IFCH = 2 GOTO 700
530 IF Z>.5 THEN PB = PB+X : PGLD = PGLD-Y : GOTO31
540 PB = PB-X : PGLD = PGLD+Y : GOTO31
600 PRINT"INTERNATIONAL UNREST..." : PGLD = PGLD + 2 * Y : PB = PB-2 *X : GOTO31
700 PRINT"MARKET RALLY ...{2 SPACES}":PG
LD=PGLD-2 *Y : PB = PB+3 *X : GOTO31