## Monday, August 27, 2012

### Petit Computer Journal #4

Petit Computer Journal #4

Knowing that computer is composed of numbers makes it easy to understand. That does not make it easy to do, you see, just to understand. The point is: The computer does what you tell it to do, not what you think you tell the computer to do. Faulty language implementation is an exception to that rule, and even then, you need to figure out a way around the problem.

Computer programming can be fun, but it can be very frustrating, indeed. The question is, what will you do to make computer programming fun? If the answer is to make games, then you're probably off to the wrong start. If the answer is to make games that people want to play, then you're probably off to the right start.

You see, computer programming is all about problem solving. What problem are you trying to solve? Without a clear goal, you probably will just do things randomly. Maybe you discover something, or maybe not. With a clear goal, however, you can work on the steps to achieving that goal. Then, when you finally solve that problem and arrive at your goal, your satisfaction level is quite high. That, my friend, is the fun of computer programming.

It's like winning a game, solving a puzzle, guessing a riddle. Before you did it, you don't know. After you did it, you know. That's fun.

Speaking of goals, you are still a beginner, so let's keep things simple for now. Let's start by figuring out how to tell a computer to do something simple.

Inkey$, input, linput

Let's get the keyboard input out of the way real quick. What is the difference between INKEY$, INPUT, AND LINPUT? Write a small program to check it out!

'Keyboard input source code example

@MAINLOOP

VSYNC 1: A$=INKEY$

IF A$!="" THEN B$=A$

LOCATE 0,0:?"A$=";A$;" "

LOCATE 0,2:?"B$=";B$;" "

GOTO @MAINLOOP

There are 3 things you have to see here:

VSYNC 1: This synchronized the system 1/60 second. Try it with different values and see what happens!

A$=INKEY$: This gets the keyboard value and assign it to A$

IF A$!="" THEN B$=A$: Since the value disappear at the next iteration, and we want to keep the old value, we assign the value of A$ to B$, but only if there is something to copy.

And that's it! If you are writing a computer game that cannot wait for user input, then INKEY$ is the way to go. I understand that it isn't the easiest to use, but it's there if you want it.

What's the difference between INPUT AND LINPUT? Try them out and see!

@MAINLOOP

VSYNC 1: INPUT "X,Y",X,Y

?"X=";X:?"Y=";Y

?:?:'DOUBLE BLANK LINES

VSYNC 1: LINPUT "DATA:";A$

?"A$=";A$

WAIT 300

GOTO @MAINLOOP

INPUT takes several inputs and assign them to different variables. This is very useful for inputting numeric values. Just type them out and separate them with comma. LINPUT takes in a string, commas included. Just one string.

Can you take string and numbers using INPUT? Try it and see!

@MAINLOOP

VSYNC 1: INPUT "X$,Y",X$,Y '<==change here

?"X=";X$:?"Y=";Y '<==Change here

?:?:'DOUBLE BLANK LINES

VSYNC 1: LINPUT "DATA:";A$

?"A$=";A$

WAIT 300

GOTO @MAINLOOP

Yes, you can! If the program doesn't understand your input, it will ask you to re-enter the data "?Redo from start". In which case, you re-enter the data, hopefully without mistake this time!

Touch Screen TCHX,TCHY,TCHST,TCHTIME PNLTYPE

Buttons and keyboard are nice, but we have something there that is just begging to be used: Touchscreen! I know I'm bucking the convention here, since most people are satisfied writing their beginner's program using INPUT or BUTTON(), but I really want to use the touch screen. Fortunately, it's as easy to use as INKEY$.

It's just some variables, and you even use it like you do INKEY$. The difference is that there is more than one, and you use numeric variables. Let's do it. It is helpful if we disable the on-screen keyboard. We do it via PNLTYPE command. Simply set it to "OFF".

'Touchscreen input source code example

PNLTYPE "OFF"

CLS

@MAINLOOP

VSYNC 1

X=TCHX:Y=TCHY:S=TCHST:T=TCHTIME

LOCATE 0,0:?"X=";X;" "

LOCATE 0,2:?"Y=";Y;" "

LOCATE 0,4:?"S=";S;" "

LOCATE 0,6:?"T=";T;" "

GOTO @MAINLOOP

Hit the Select button to stop the program. Yup. Just like INKEY$. The difference is, X and Y values are not reset to zero when the stylus is off the screen even though the status (TCHST) and timer (TCHTIME) are reset.

Math - Arithmetic

Alright, I need you to confess: Who among you have not yet finished 1st Grade? You know, the school grade right after Kindergarten? Whaat? You don't know Arithmetic? Oh, dear. This is bad. I think maybe you need to learn how before we can continue.

Haha, joking aside, you do need to know Arithmetic. Some Trigonometry, too. How about Algebra? Yes, you do need to know how to manipulate variables. Fortunately, if you know Show-and-Tell, you may be alright. Here's a little something that's useful to know: Mapping function.

map() is something that is built-in in Processing computer programming language. It's a good programming language. Check out www.processing.org for details.

In the meantime, let's implement it in BASIC. The idea is, if you have a number that is between two numbers, given another two numbers, what will be the number that has the same ratio as the first? In mathematical format, assuming X is the first number, and Y is the second, we have

X1-X2-X3 X2 is between X1 & X3

Y1-Y2-Y3 Y2 is between Y1 & Y3

Since the ratio is the same, we have

(X2-X1)/(X3-X1)=(Y2-Y1)/(Y3-Y1)

Solve for Y2:

(Y2-Y1)/(Y3-Y1)=(X2-X1)/(X3-X1)

(Y2-Y1)=((X2-X1)/(X3-X1))*/(Y3-Y1)

Y2=(((X2-X1)/(X3-X1))*/(Y3-Y1))+Y1

And that's all there is to it! Work it out on paper if you're having trouble. I find it helpful to draw triangles to visualize the problem.

A Math Explorer sample program

We want to feature a lot of math here, so we're going to just do it all in one program. The program will features different modes, and take inputs from touch screen, normalized to 0-5 for both X and Y. Furthermore, if the stylus is on top-left corner, we'll change the mode.

0: Simple Arithmetic

1: Math functions

2: Logical Math

3: Exponent

Here goes:

Part 1: Touch screen input. No problem there. Just copy it from the sample program above.

'Math Explorer

PNLTYPE "OFF"

CLS

@MAINLOOP

VSYNC 1

X=TCHX:Y=TCHY:S=TCHST:T=TCHTIME

Part 2: Display X,Y, Mode, and Cycle Mode. If you remember our COUNTER program example? Yup, just like that!

IF (X<32 AND Y<24 AND T==1) THEN MODE=MODE+1

MODE=MODE%4:'MODE=0-3

LOCATE 0,0

?"X=";X;" Y=";Y;" MODE=";MODE

Part 3: Normalize X and Y. We already have the mathematical formula for this. Just implement that using GOSUB.

X1=0:X2=X:X3=255:Y1=0:Y3=5:GOSUB @MAP:XP=Y2:'CALCULATES XP=Y2

X1=0:X2=Y:X3=191:Y1=0:Y3=5:GOSUB @MAP:YP=Y2:'CALCULATES YP=Y2

?"XP=";XP;" YP=";YP;" "

GOTO @MAINLOOP

@MAP

Y2=(((X2-X1)/(X3-X1))*(Y3-Y1))+Y1

RETURN

And that's the beginning. We'll continue with Part 4 next, but first, run this program and see that we have normalized XP and YP, and that the MODE cycles 0-3 satisfactorily.

Change the program slightly to this before continuing. Yes, I expect you to be able to read! I know it's hard in the beginning, but please persevere.

'Math Explorer

PNLTYPE "OFF"

CLS

@MAINLOOP

VSYNC 1:IF MODE!=2 THEN CLS

X=TCHX:Y=TCHY:S=TCHST:T=TCHTIME

IF (X<32 AND Y<24 AND T==1) THEN MODE=MODE+1

MODE=MODE%4:'MODE=0-3

LOCATE 0,0

?"X=";X;" Y=";Y;" MODE=";MODE;" "

X1=0:X2=X:X3=255:Y1=0:Y3=5:GOSUB @MAP:XP=Y2:'CALCULATES XP=Y2

X1=0:X2=Y:X3=191:Y1=0:Y3=5:GOSUB @MAP:YP=Y2:'CALCULATES YP=Y2

?"XP=";XP;" YP=";YP;" "

GOTO @MAINLOOP

@MAP

Y2=(((X2-X1)/(X3-X1))*(Y3-Y1))+Y1

RETURN

And that's the program. Now, here is some snippets of code. I trust that you know where to put this.

?:?

ON MODE GOTO @ARIT, @FUNC,@LOGI, @EXPO

GOTO @MAINLOOP:'INVALID CHOICE

@ARIT

?"X+Y=";(X+Y)

?"X-Y=";(X-Y)

?"X*Y=";(X*Y)

IF Y!=0 THEN ?"X/Y=";(X/Y)

IF Y!=0 THEN ?"X%Y=";(X%Y)

IF YP!=0 THEN ?"X%YP=";(X%YP)

GOTO @ENDLOOP

@FUNC

?"FLOOR(XP)=";FLOOR(XP)

?"RND(X)=";RND(X)

?"RND(XP)+20=";RND(XP)+20

?"ABS(X-128)=";ABS(X-128)

?"SGN(X-128)=";SGN(X-128)

?"SWAP ":SWAP XP,YP

?"XP=";XP;" YP=";YP

IF S==1 THEN WAIT 30

GOTO @ENDLOOP

@LOGI

LOCATE 0,4

?"X= ";:V=X:GOSUB @BIN

?"Y= ";:V=Y:GOSUB @BIN

?"AND ";:V=(X AND Y):GOSUB @BIN

?"OR ";:V=(X OR Y):GOSUB @BIN

?"XOR ";:V=(X XOR Y):GOSUB @BIN

?

?"X= ";:V=X:GOSUB @BIN

?"NOT ";:v=NOT(X):GOSUB @BIN

?"! ";:v=!X:GOSUB @BIN

GOTO @ENDLOOP

@EXPO

?"SQR(X)=";SQR(X)

?"EXP(XP)=";EXP(XP)

IF X!=0 THEN ?"LOG(X)=";LOG(X)

?"POW(2,XP)=";POW(2,XP)

?"POW(3,XP)=";POW(3,XP)

@ENDLOOP

GOTO @MAINLOOP

'SPLIT THIS TO THE END

@BIN

FOR I=0 TO 7

P=POW(2,I)

IF (P AND V) THEN ?"1"; ELSE ?"0";

NEXT

RETURN

One more round of Math and we'll be done! It's all about Trigonometry. We'll save it for later until after we learn Graphics!

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