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Spellcaster presents: TTTTTTTTTT HH HH EEEEEEEEEE MM MM AAAA GGGGGGGGG TT HH HH EE MMM MMM AA AA GG TT HH HH EE MM M M MM AA AA GG TT HHHHHHHHHH EEEEEE MM MM MM AAAAAAAA GG TT HH HH EE MM MM AA AA GG GGGG TT HH HH EE MM MM AA AA GG GG TT HH HH EEEEEEEEEE MM MM AA AA GGGGGGGG Issue 1 25-9-95 ■ Index 1. Introduction 1.1. About the magazine 1.2. About the author 1.3. Distribution 1.4. Contribuitions 1.5. Hellos and greets 2. Hexadecimal and binary - The untold story 2.1. What are they ? 3. Bits and bytes - To they really bite ? 3.1. What are they ? 3.2. The relatives 4. Introduction to Pascal 4.1. What is Pascal 4.2. The IDE 4.3. How to build a program in Pascal - Your first program 4.4. Variables 4.5. The Writeln and Readln keywords 5. Our friend, the pointer - Part I 5.1. What the hell is a pointer ? 5.2. What's the use ? 5.3. How can I use a pointer ? 6. Points of view 7. The adventures of Spellcaster, part 1. ■ Introduction ■ About the magazine Welcome to the first issue of 'The Mag', the electronic magazine, brought to you by Spellcaster, alias Diogo de Andrade. Ok, ok, I know the magazine has a crapy name, but it was the only thing I could think of. This magazine is dedicated to all the programmers and would-be programmers out there, to those who wish to learn how to program anything, from demos to games, passing through utilities and all sort of thing your mind can think of. When you read this magazine, I'll assume some things. First, I assume you have Borland's Turbo Pascal, version 6 and upwards. I'll also think you have a 80386 (or 386 for short; a 486 would be even better), a load of patience and a sense of humor. This last is almost essencial, because I don't receive any money for doing this, so I must have fun doing it. I will also take for certain you have the 9th grade (or equivelent). As I stated above, this magazine will be made especially for those who don't know where to get information, or want it all in the same place, and to those who want to learn how to program, so I'll try to build knowledge, building up your skills issue by issue. If you sometimes fail to grasp some concept, don't despair; try to work it out. That's what I did... Almost everything I know was learnt from painfull experience. If you re-re-re-read the article, and still can't understand it, just drop me a line, or just plain forget it. Most of the things I try to teach here aren't linked to each other (unless I say so), so if you don't understand something, skip it and go back to it some weeks later. It should be clearer for you then. Likewise, if you see any terms or words you don't understand, follow the same measures as before. Ok, as I'm earing the Net gurus and other god-like creatures talking already, I'm just going to explain why I use Pascal. For starters, Pascal is a very good language, ideal for the beginner, like BASIC (yech!), but it's powerfull enough to make top-notch programms. Also, I'll will be using assembly language in later issues, and Pascal makes it so EASY to use. Finally, if you don't like my choice of language, you can stop whining. The teory behind each article is very simple, and common with any of the main languages (C, C++, Assembly - Yes, that's true... BASIC isn't a decent language). Just one last thing... The final part of the magazine is a little story made up by my distorted mind. It's just a little humor I like to write, and it hasn't got nothing to do with programming (well, it has a little), but, as I said before, I just like to write it. ■ About the author Ok, so I'm a little egocentric, but tell me... If you had the trouble of writing hundreds of lines, wouldn't you like someone to know you, even by name ? My name is Diogo de Andrade, alias Spellcaster, and I'm the creator, editor and writer of this magazine. I live in a small town called Setúbal, just near Lisbon, the capital of Portugal... If you don't know where it is, get an encyclopedia, and look for Europe. Then, look for Spain. Next to it, there's Portugal, and Setúbal is in the middle. I'm 18 years old, and I just made it in to the university (if you do want to know, I'm in the Technical Institute of Lisbon, Portugal), so I'm not a God-Like creature, with dozens of years of practice (I only program by eight years now), with a mega-computer (I own a 386SX, 16 Mhz), that wear glasses with lens that look like the bottom of a bottle (I use glasses, but only sometimes), that has his head bigger than a pumpkin (I have a normal sized head) and with an IQ of over 220 (mine is actually like 180). I can program in C, C++, Pascal, Assembly and even BASIC (yech!). So, if I am a normal person, why do I spend time writing this ? Well, because I have the insane urge to write thousands of words every now and then, and while I'm at it, I may do something productive, like teaching someone. I may be young, but I know a lot about computers (how humble I am; I know, modesty isn't one of my qualities). Just one more thing, if you ever program anything, please send to me... I would love to see some work you got, maybe I even could learn something with it. Also, give me a greet in your program/game/demo... I love seeing my name. ■ Distribution I don't really know when can I do another issue, so, there isn't a fixed space of time between two issues. General rule, I will try to do one every two weeks, maybe more or maybe less. 'The Mag' is available by the following means: - Snail Mail : My address is below, in the Contributions seccion... Just send me a disk and tell me what issues you want, and I will send you them... - E-Mail : If you E-mail me and ask me for some issues, I will Email you back with the relevant issues attached. - BBS's : I don't know for sure what BBS's have or will have my magazine, but I will try to post it in the Skyship BBS. If you have a BBS and you want to receive 'The Mag', contact me. Skyship BBS numbers: (351)+01-3158088 (351)+01-3151435 By the end of this year (1995), I should have an Internet Page, and some more BBS's in my list, besides some ftp's. ■ Contributions I as I stated before, I'm not a God... I do make mistakes, and I don't have (always) the best way of doing things. So, if you think you've spotted an error, or you have thought of a better way of doing things, let me know. I'll be happy to receive anything, even if it is just mail saying 'Keep it up'. As all human beings, I need incentive. Also, if you do like to write, please do... Send in articles, they will be welcome, and you will have the chance to see your names up in lights. If anyone out there has a question or wants to see an article about something in particular, feel free to write... All letters will be answered, provided you give me your address. Also, I'm looking for people to create a new demo/game/utilities group, and I need all sort of people, from coders (sometimes, one isn't enough), musicians (I can compose, but I'm a bit limited), graphics artists (I can't draw nothing) and spreaders... I mean, by a spreader, someone who spreads things, like this mag. If you have a BBS and you want it to include this magazine (or anything that I make), feel free to write me... You can also contact me personally, if study on the IST (if you don't know what the IST is, you don't study there). I'm the freshman with the black hair and dark-brown eyes... Yes, the not-so-tall but pretty one (there goes my modesty again). I recommend you to contact me personally, if you can, especially if you are a member of the opposite sex (I'm a man, for those of you who are wondering). My adress is: Praceta Carlos Manito Torres, nº4/6ºC 2900 Setúbal Portugal Email: dgan@rnl.ist.utl.pt ■ Hellos and greets I'll say hellos and thanks to all my friend, especially for those who put up with my constant whining (you know who you are). Special greets go to Denthor from Asphyxia (for the excelent VGA trainers), Draeden from VLA (for assembly tutorials), Joaquim Elder Guerreiro, alias Dr.Shadow (Delta Team is still up), Alex "Darkfox" (thanks for letting me use your BBS), Joäo Neves and Henrique Craveiro for sugestions, and all the demo groups out there. I also want to say hi to my idols (I know they don't read this, but...), Chris Roberts, François Lionet, Archer MacLean, everybody at ID Software and Apogee, Sierra On-Line, Lucas Arts and Team 17, for showing me what programming is all about. ■ Hexadecimal and binary - The untold story This article is about hexadecimal and binary. This is a purely teorical article, so, if you know everything about them, go on to the next part. ■ What are they ? Hexadecimal (Hex for short) and binary are diferent numbering sistems. An more common example of a numbering sistem is the decimal sistem, that we use everyday. The teory behind decimal is that there are 10 digits, starting from 0 up to 9. If you join the digits together, you will get the numbers. This is called a base 10 sistem. The hexadecimal sistem is a base 16 sistem. This means you have the digits from 0 to 9, but after 9 you still have A, B, C, D, E and F. Don't worry if this sound a little weird. It will be a lot simpler when you look at the next chart. The first column is the number in decimal, the other one is the hexadecimal correspondent. ┌─────────────┬──────────────┐ ┌─────────────┬──────────────┐ │ DECIMAL │ HEX │ │ DECIMAL │ HEX │ ├─────────────┼──────────────┤ ├─────────────┼──────────────┤ │ 0 │ 0 │ │ 16 │ 10 │ │ 1 │ 1 │ │ 17 │ 11 │ │ 2 │ 2 │ │ 18 │ 12 │ │ 3 │ 3 │ │ 19 │ 13 │ │ 4 │ 4 │ │ 20 │ 14 │ │ 5 │ 5 │ │ 21 │ 15 │ │ 6 │ 6 │ │ 30 │ 1F │ │ 7 │ 7 │ │ 31 │ 20 │ │ 8 │ 8 │ │ 40 │ 28 │ │ 9 │ 9 │ │ 50 │ 32 │ │ 10 │ A │ │ 60 │ 3C │ │ 11 │ B │ │ 70 │ 46 │ │ 12 │ C │ │ 80 │ 50 │ │ 13 │ D │ │ 100 │ 64 │ │ 14 │ E │ │ 200 │ C8 │ │ 15 │ F │ │ 255 │ FF │ └─────────────┴──────────────┘ └─────────────┴──────────────┘ Do you understand it now ? I'll teach you how to convert from one base to another in a second. Another thing you must know, is that that hexadecimal number is almost everytime acompained with the '$' simbol or with the letter 'h' in the end of it. So, $10 is the same that 10h, and it means 16 in decimal. But how do you convert from a base to another, I hear you cry. It's easier explain with an example. Let's convert the number 255 decimal to hexadecimal (I know by experience that 255 decimal is FFh or $FF). You divide the 255 by 16. Then, 255 │ 16 you convert the quocient to 15 └───── hexadecimal (in this case it equals 15 F ) and then convert the reminder (again it's F). So you finish with $FF. Let's try again... Convert the number 654 to hex... This time it's more tricky, but try for yourself, then check the result. 654 │ 16 14 = Eh <-- 14 └─────┐ 40 │ 16 So, 654 = 28Eh 8 └───── 2 Now, let's try to do the opposite, that is, convert from hexadecimal to decimal. This is easier to do. All you have to do is to know the powers of 16. Let's convert FFh to decimal (you already should know this is equal to 255). FF = 15 * 16 + 15 = 255 ; Probably, you didn't understood it, so I'll explain it better. 16^3 16^2 16^1 16^0 ; These are the powers of 16. 4096 256 16 1 0 0 F F ; this is the number we want to convert 00FFh = FFh Now, we multiply the second F (counting from the right) by 16. F*16 = 15*16 = 240; and then you add the other F; 240+F = 240+15 =255. See, how it was easy ?! Let's try with another number... Let's convert 28Eh to decimal. 16^3 16^2 16^1 16^0 4096 256 16 1 0 2 8 E So, we get: 256*2 + 8*16 + E = 512 + 128 + 14 = 654 !!! I know this sound complicated for a begginner, but it will all sound clearer in time. Don't be scared by it... Don't let it prevent you from making programming masterpieces. Some of these things aren't usefull, for now, but they'll proove invaluable in the future, so I decided that it would be better if you learned it now. So, the article's about hexadecimal and BINARY... So, let's talk binary for now. Has you probably has guessed, binary is another numbering sistem, this time a base 2 sistem... Yep, that's right a sistem that only has two digits, the 0 and the 1. So, let's do another table... ┌─────────────┬──────────────┐ ┌─────────────┬──────────────┐ │ DECIMAL │ BINARY │ │ DECIMAL │ BINARY │ ├─────────────┼──────────────┤ ├─────────────┼──────────────┤ │ 0 │ 00000000 │ │ 16 │ 00010000 │ │ 1 │ 00000001 │ │ 17 │ 00010001 │ │ 2 │ 00000010 │ │ 18 │ 00010010 │ │ 3 │ 00000011 │ │ 19 │ 00010011 │ │ 4 │ 00000100 │ │ 20 │ 00010100 │ │ 5 │ 00000101 │ │ 21 │ 00010101 │ │ 6 │ 00000110 │ │ 30 │ 00011110 │ │ 7 │ 00000111 │ │ 31 │ 00011111 │ │ 8 │ 00001000 │ │ 40 │ 00101000 │ │ 9 │ 00001001 │ │ 50 │ 00110010 │ │ 10 │ 00001010 │ │ 60 │ 00111100 │ │ 11 │ 00001011 │ │ 70 │ 01000110 │ │ 12 │ 00001100 │ │ 80 │ 01010000 │ │ 13 │ 00001101 │ │ 100 │ 01100100 │ │ 14 │ 00001110 │ │ 200 │ 11001000 │ │ 15 │ 00001111 │ │ 255 │ 11111111 │ └─────────────┴──────────────┘ └─────────────┴──────────────┘ So, this is fairly simple, isn't it ?! Let's do some conversion... This is just like the decimal to hexadecimal conversion, but you divide by two... 255 │ 2 1 └────┐ 127 │ 2 1 └────┐ 63 │ 2 1 └────┐ 31 │ 2 So, 255 = 11111111b 1 └────┐ | 15 │ 2 \|/ 1 └────┐ This is the 7 │ 2 same as the 'h' in 1 └────┐ hexadecimal... 3 │ 2 1 └──── 1 See, how easy this is... And converting from binary to decimal is as easy as PI = 3.141592654. In this case, you must know the powers of two. 2^7 2^6 2^5 2^4 2^3 2^2 2^1 2^0 128 64 32 16 8 4 2 1 1 1 1 1 1 1 1 1 128 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 255 So, we come to the breath-taking conclusion that 255 = 11111111b... Can you believe it ? Another example: converting 10010001b. 2^7 2^6 2^5 2^4 2^3 2^2 2^1 2^0 128 64 32 16 8 4 2 1 1 0 0 1 0 0 0 1 128 + 16 + 1 = 145 You have now taken the first steps into a larger world... The cyber-world. You know what hexadecimal and binary are... I'll let it to you to discover how to convert from hexadecimal to binary and vice-versa... It's also easy... Trust me on this. To those super-programmers how were reading this just to know the untold story of hexadecimal and binary, you are in for a surprise... There isn't an untold story !!! That's all folks !... ■ Bits and bytes - Do they really bite ? No they don't, answering to the pending question. Let's delve into the world of bits and bytes, and know all about their family. ■ What are they ? You must know something about computers, as you read this article. Computers are very stupid... They can only understand something: 0's and 1's. You may be asking to yourselfs 'What is he talking about ?'. For starters, the computer only operates with 0's and 1's (active and desactive, on and off, true of false). In the dawn of computers, everything was made by a neverending serie of 1's and 0's. This is known as a bit. The bit is either 0 and 1 (sound's familiar with binary). The computer can then perform a series of operations on them, but now, this is unimportant. That's why the binary notation is very important in computers. As you may have guessed, the computer wouldn't be very usefull if it could only manage 0's and 1's. So the byte was invented. The byte is a serie of bits join together (8 of them). As a byte has 8 bits, it can store values that go from 00000000b to 11111111b (that is, from 0 to 255). To make this clearer with this example: Imagine a switch: ┌───┐ │ │ <-- this is a switch. └───┘ Now, a any switch, it can be on or off: ┌───┐ ┌───┐ │ 0 │<-- This switch is off │ 1 │<-- This switch in on └───┘ └───┘ This is a bit... A byte is just a serie of 8 switches, some of them are on, some of them are off. So: ┌───┐┌───┐┌───┐┌───┐┌───┐┌───┐┌───┐┌───┐ │ 0 ││ 1 ││ 0 ││ 1 ││ 1 ││ 0 ││ 0 ││ 1 │ -> This is a byte, that └───┘└───┘└───┘└───┘└───┘└───┘└───┘└───┘ holds the number 89. Ok, so now we know waht a bit and a byte are. ■ The relatives Like every unit, the bit and the byte have multiples. The middle brother of the byte family is the word. The word is equal to two bytes. So now, you can store numbers that range from 0 to 65535, because you have another byte to store things. The oldest brother is the Double Word, or Dword. As you probably guessed, this is two words together, or four bytes. This gives you a very big number to store... I think is from 0 to 4.294.967.295, give and take some. Next you have the father of byte, word and Dword: Mr.Kilobyte, or Kb for short. This is equal to 1024 bytes (not 1000 as the name sugests). This measure used to say the capacity of a disk or memory. But, even in the byte family there is the grandfather: Grandpa Megabyte, also known as Mb and Mo. Well this is equal to 1024 Kb, or 1.048.576 bytes. Finally, you have the grand-grandfather... He is called Gigabyte and he is very big... It has 1024 Mb, so that a whole lot of bytes... So, now you know all about the byte family, from the humble byte to the mighty gigabyte. I know this sound a bit strange, but it will soon grow within you. As I said before, you musn't be desmotivated by it, because most of these things will become part of your knowledge with time. It will become like your second language (ok, like your third, if you are portuguese and you know english). Soon you will be playing with them without trouble. ■ Introduction to Pascal ■ What is Pascal Technically, Pascal is a high-level programming language. Poetically, it is the tool that makes dreams come true... What Pascal really is is a translator. It converts 'sentences' that ressemble a normal talking and writing language to binary codes the computer can execute. This process is know as compiling. It was invented in the seventies (I think) by a professor that wanted a language that was easy to learn (as BASIC), yet powerfull. You must be thinking what differs from Pascal and BASIC (by now, you must have realised that I hate BASIC). Well, the difference is that BASIC is an interpreter, while Pascal is a compiler. A interpreter functions like this: ┌─> Get untranslated command │ Translate command └── Execute translated command The compiler works like this: Translate all commands ┌─> Get translated command └── Execute translated command It doesn't take an Einstein to figure out that a compiler is faster than a interpreter. There's all sort of little diferences beetween them, appart from this, but they are all about restrictions. General rule is the interpreter is more limited than a compiler. The interpreter is easier to understand, that is true, but it's very limited all the same. ■ The IDE It's a bit weird for me teaching the fundamental about Pascal. There's so much to teach, and I don't know where to start. I'll start with the editor. When you first startup Pascal, (by typing 'turbo' or something like it in the DOS), you will get a blue window, with a white frame, with a series of menus in the toolbar above it. Don't worry if the window doesn't appear. Just press ALT+F. The File menu will expand. Select then the New option, either with the arrow keys and Return, or pressing the 'N' key. You are now looking to the IDE... The Integrated Development Enviroment. This is where you are going to write your future masterpieces. I'll teach you how to do things as we progress throughout the magazine. ■ How to build a program in Pascal - Your first program Every program in Pascal must start with a phrase like: PROGRAM myprogram(input,output); or PROGRAM myprogram(output); or PROGRAM myprogram(input); or This isn't really necessary (with Pascal 6 and upwards), but it's good programming practice to put it there. The word 'PROGRAM' is a keyword. A keyword is a word that Pascal recognizes (if you use Pascal V7.0, it will turn white, as opposing the rest of the yellow text). As I was saying, 'PROGRAM' is a keyword that says to the compiler the name of the program (in this cases, the name is myprogram), and what kind of program it is. In the first case, the program is (input,output), that is, the program receives and writes data. By data, I mean any kind of data, is it key, joystick or mouse commands, images, sounds, etc... Data can be anything at all you want. In the second case, the program only outputs, that is, it only gives out data. In the third case, you have an unusual case, seldom used. It is the input only program. That only receives data. Also notice the semi-colon in the end of the 'phrase'. It is necessary you write it. Almost every command in Pascal ends with a ';'. At first you will probably forget to put it, but when you run a program (that is, when you compile it), Pascal will warn about it and will not run the program. As I teach you new commands, I will tell which ones don't need the semi-colon. If I don't say nothing about it, assume the command needs it. The next thing in the program is the keyword 'BEGIN'. This tells the compiler that a block of instructions follows. There are 5 kinds of instruction blocks, and I will talk about all of them, in time. For the meanwhile, in this case, this 'BEGIN' tells us that the main program block starts there. Notice: For every 'BEGIN', there's and 'END', that is, the last line in your program should be 'END.'. Also notice that the 'BEGIN' keyword is never followed by a semi-colon, while the 'END' does, except if it is the end of the program, in which case it is followed by a dot. Let's see an example: Program Do_Nothing; { you can omit the (input,output) } Begin End. This program would compile, but it wouldn't do nothing. Another thing to know about a Pascal program is that the compiler ignores anything that is enclosed by '{' and '}'. So, you can write comments on the program, just make sure you open and close the brackets. Ok, let's make a program that actually makes something... Program Hello(output); { This is the title of the program, } { that only outputs... } Begin { Begining the main block } Writeln('Hello everybody'); { Writes 'Hello everybody' in the screen} Readln; { Waits for RETURN to be pressed } End. { Ends the main block and exits program} Type in this code (another name for the program) and run it. To run the program, press ALT+R. The Run menu will pop up. Press 'R' now, and the program will compile. Then it will write in the screen 'Hello everybody'. Then it will wait for you to press RETURN and it will return to the IDE. Another way to run the program is to press CTRL+F9. About the 'WRITELN' and 'READLN' keywords, I will refer to them later on. Now, let's save your program. Go to the File menu (ALT+F) and then press 'S'. A file browser will appear. Write the filename of your program (something like 'HELLO') and press RETURN. The program will be saved. If you didn't specified the extension, Pascal will assume '.PAS'. I recommend you to make a directory to hold your Pascal programs, so you always know were they are. I know you must be thinking: 'Ow ! Big deal, I made a sentence appear in the screen'. I know this isn't impressive, but it's a beginning. At first this is off-putting, but as you progress you will see better results. I tought I'd stop for now, but I hear you cry: 'More! We want more!'. So here it goes... ■ Variables This is one of the more important things in programming, so pay attencion. A variable is a place where you can store data of various types. A variable (also called a var) in Pascal must be defined before the beginning of the main block of your program. Here's a list of some of the types of variables there exists, alongside with their description. ┌───────────────────┬────────────────────────────────────────────────────┐ │ Type │ Description │ ├───────────────────┼────────────────────────────────────────────────────┤ │Shortint │A signed integer number (a number that can be │ │ │positive and negative) that ranges from -128 to 127 │ │ │ │ │Integer │A signed integer number that ranges from -32768 to │ │ │32767 │ │ │ │ │Longint │A signed integer number that ranges from -2147483648│ │ │to 2147483647 (very big!) │ │ │ │ │Byte │An unsigned integer number that ranges from 0 to 255│ │ │ │ │Word │An unsigned integer number that ranges from 0 to │ │ │65535 (sounds familiar ?!) │ │ │ │ │Char │A simple character... Think of it as a letter... │ │ │ │ │String │A collection of Char's... It's like a sentence. │ └───────────────────┴────────────────────────────────────────────────────┘ These are only some of the types of vars that exist in Pascal... There are many others and you can even define new ones, but that's something I'll talk about in many issues from now... You are probably wondering what the hell is that all about... Let me demonstrate with a series of example programs... They are all commented, so you will probably understand them. Program Test_1; { This starts the program Test_1 } { This program shows you how to give define and give } { values to variables } Var A:Integer; { This defines a var of type Integer and calls it A } B:Word; { This defines a var of type Word and calls it B } C:Char; { This defines a var of type Char and calls it C } D:String; { This defines a var of type String and calls it D } Begin A:=0; { This gives var A the value 0 } B:=50; { This gives var B the value 50 } C:='B' { This stores in var C the letter B } D:='Hello' { This stores in var D the word 'Hello' } Writeln(A); { This writes to the screen the content of var A } Writeln(B); { This writes to the screen the content of var B } Writeln(C); { This writes to the screen the content of var C } Writeln(D); { This writes to the screen the content of var D } Readln; { This waits for RETURN to be pressed } End. { This ends the program } Program Test_2; { This starts the program Test_2 } { This program shows you how to do some operations with} { variables } Var Num1:integer; { This defines a var of type Integer and calls it Num1 } Num2:Word; { This defines a var of type Word and calls it Num2 } Word1:String; { This defines a var of type String and calls it Word1 } Word2:String; { This defines a var of type String and calls it Word2 } Begin Num1:=15; { This gives var Num1 the value 15 } Num2:=50; { This gives var Num2 the value 50 } Word1:='Hello'; { This stores in var Word1 the word 'Hello' } Word2:='World'; { This stores in var Word2 the word 'World' } Num1:=Num1+Num2; { This adds Num1 to Num2 and places the result in Num1 } Word1:=Word1+Word2; { This adds Word1 to Word2 and places the result in } { Word1 } Writeln(A); { This writes to the screen the content of var A } Writeln(B); { This writes to the screen the content of var B } Writeln(C); { This writes to the screen the content of var C } Writeln(D); { This writes to the screen the content of var D } Readln; { This waits for RETURN to be pressed } End. { This ends the program } Did you understand it ? It's quite easy when you get the hang of it. Play with the programs and you'll see how it works. You can execute all sort of operations with variables, and even include more than one operation at a time. They are very flexible, but notice a few things: - If you have a var of type Char and you give the value 'ALFA', this is the same that giving that variable the value 'A', because the var is type Char, that only handles one character. - When you want to give a value to a variable, you must include ':' after it. If you don't, you will get an error message. A:=10; { This is ok } A=10; { this wouldn't compile } - You can specify the maximum number of characters a string can hold, putting the maximum number of characters (chars for short) it can hold in front of it, enclosed in square braquets. Var S:String[14]; { This defines the string S, with 14 chars } Then, when you write something like: S:='SPELLCASTER RULES' It would be 'clipped', that is, the variable S would get the value 'SPELLCASTER RU', that is only 14 chars long... - There's a limit of memory the Pascal reserves for variables, so you can't define an infinite number of variables. This limit is for now of 64 Kb, but don't worry about it by now, because you won't make variables that can ocupy that space. So that you know, a var of type integer ocuppies 2 bytes ! So, you can store 32768 integer vars in memory ! Next there is examples of the operations you can do with ordinal type of variables, which are Shortint, Integer, Longint, Byte and Word. I'll use just words, but it's the same for all the ordinal types of variables. This isn't a program... It's just some examples: Var A,B:Word; { Defines variables A and B as Words } A:=10; B:=15; { You can put multiple commands in one line, as long as they } { separeted by a semi-colon. } A:=A*B; { Multiplies A by B and stores result in A } A:=A DIV B; { Divides A by B and stores result in A } A:=A+B; { Adds A to B and stores result in A } A:=A-B; { Subtracts B from A and stores result in A } B:=A MOD B; { Divides A by B and stores the modulo in B } A:=A+1; { Adds one to A and stores result in A } B:=A+42; { Adds 42 to A and stores result in B } B:=200-A; { Subtracts A from 200 and stores result in B } B:=A+B*2; { Multiplies B by 2, adds that to A and stores result in B } I think this cover the main operations. Don't forget the following points: - The DIV operation gives the integer result of the division, that is, if you divide 15 by 2, you will get 7. The decimal part is ignored. - The order in which operation are made are equal to the standart order in normal maths, except that the computer calculates from right to left, while normal maths do operations from left to right. The order can be altered by using parentesis. So: A:=A+B*2; { Multiplies B by 2, adds that to A and stores result in A } A:=(A+B)*2; { Adds A to B, multiplies that by 2 and stores result in A } Now, let's cover the string maths... this is quite unusual, because, normaly you can only add numbers. Though it's strange, it's simple, as there is only one operation (by now)... Var A,B:String; { Defines A and B as strings } A:='Spell'; { Gives A the value 'Spell' } B:='caster'; { Gives B the value 'caster' } A:=A+B; { Adds A to B and stores result in A; A='Spellcaster' } A:=A+' Rules';{ Adds A to ' Rules' and stores result in A, } { so A='Spellcaster Rules' } Simple isn't it ? Keep practicing and you'll reach perfection. This is quite easy, but, for a beginner it can be complicated, because it's a new concept. ■ The WRITELN and READLN keywords These are one of the more helpfull commands for beginners. Basically, what they do is Write and Read... Tough, isn't it ?! Ok, let's examine WRITELN keyword. It's sintax (sintax is how you call the command) is: WRITELN (what to write); The 'what to write' in parentesis is just that... It's what you want to write. It can be almost anything you want. If you don't write nothing, he just skips a line. Let's go to an example: Program Test_3 { Defines program Test_3 } Var A:String; { Defines variable A as a string } B:Word; { Defines variable B as a word } Begin { Begins the main block } A:='Spellcaster'; { Gives var A the value 'Spellcaster' } B:=1995; { Gives var B the value 1995 } Writeln(A); { Writes the content of variable A } Writeln(B); { Writes the content of variable B } Writeln('We are in ',B); { Writes 'We are in ', followed by var B } Readln; { Waits for RETURN to be pressed } End. { Ends the program } Now, try and change the WRITELN's in the program for WRITE's only (yes, that's right... No LN ! ). If you do this, you will notice that the word 'Spellcaster' will appear followed imediattly by the number 1995. The diference between WRITELN and WRITE is that WRITELN changes line after writing. WRITELN can also be used to write to the printer, but I'll save that for a future issue. Say kids, what time is it ? It's time to move on to READLN. We have just seen one of the uses of READLN in previous programs. It can be used to wait for a person to press RETURN, but that's just the tip of the iceberg... As you may have noticed (if you executed the above shown programs) is that if you press any key besides RETURN, while the program is waiting, is that the text you type in appears on the screen. This is a very usefull thing and I'm going to show you why: Program Test_4; { This starts program Test_4 } Var A:String; { Defines a string called A } Begin { Starts main block } A:='Spellcaster'; { Gives var A the value 'Spellcaster' } Writeln(A); { Writes the content of var A on the screen } Readln(A); { Reads a new value for variable A... } Writeln(A); { ...and writes it in the screen. } Readln; { Waits for RETURN to be pressed } End. { Ends program } See why READLN is so usefull ?! It gives you the hability to read the value of a variable from the keyboard. So, now you know somethings to keep you entertained until the next issue. Play with the programs, try to understand it and, especially, try to do a program alone... You can do it with some patience. It's not that hard... I will leave this section with one last program. I won't do what it does, so you'll have to type it in. The only thing I say is that this program uses a lot of the things we talked today. I won't comment it on purpose, to make you read it to understand it. Program Maths(Input,Output); Var A,B:Integer; C:Integer; Begin Writeln('The Maths Version 1.0'); writeln; write('Type in number A : '); readln(A); write('Type in number B : '); readln(B); C:=A+B; Writeln('A+B=',C); C:=A-B; Writeln('A-B=',C); C:=A*B; Writeln('A*B=',C); C:=A DIV B; Writeln('A DIV B=',C); C:=A MOD B; Writeln('A MOD B=',C); Readln; End. ■ Our friend, the pointer - Part I This article is aimed to those of you who already know some programming. If you are a beginner, skip this article, get some more issues of 'THE MAG', learn what you can with it, and then return to this issue. ■ What the hell is a pointer ? A pointer, as the name sugests is a type of variable that points to something. That something it's usually a position in memory. ■ What's the use ? Imagine you want to create a array of some kind, let's say a 320 by 200 array of type byte. Normally you would do like this: Var A:Array[1..320,1..200] of byte; If you would try to compile a program with a line like this, you would, but you finished up beeing without space for the other variables in the program, because, as you may know, Pascal has a 64Kb limit for variables. What's the solution for this? Pointers, of course !!! ■ How can I use the pointer ? There's three ways of using a pointer: two of them are dynamic (read by that harder, because they don't have a fixed size) and one not-dynamic. I'll teach you the not-dynamic one, because it's very easy. I'll save the dynamic solution some issues away from now. Normally, if Pascal had a bigger than 64Kb limit for variables, you could a program like this (the dots are other code that doesn't matter): Program Test_5; Var A:Array[1..320,1..200] of byte; B:Array[1..320,1..200] of byte; Begin ....... ....... ....... ....... A[221,2]:=1; B[300,43]:=2; ....... Write(A[221,2]); Write(B[300,43]); ....... ....... ....... End. This wouldn't compile, because it excedes the 64Kb limit. To do this in Pascal, with the 64Kb limit, you must do it like this: Program Test_5; Type C=Array[1..320,1..200] of byte; Var A:^C; B:^C; Begin Getmem(A,Sizeof(A^)); Getmem(B,Sizeof(B^)); ....... ....... ....... A^[221,2]:=1; B^[300,43]:=2; ....... Write(A^[221,2]); Write(B^[300,43]); ....... ....... ....... Freemem(A,Sizeof(A^)); Freemem(B,Sizeof(B^)); End. This second program would work because you would be spending base-memory of the computer, and not the 64Kb Pascal has for variables. Now, for the hard part: explaining how this works. The TYPE clause in the start is necessary, because who need to point to something when we define the A and B variables. You place there wherever you want to allocate in base memory. The VAR clause says that vars A and B point to an object with the structure of type C. Then, you must allocate the memory for the pointer. So, you use the Getmem keyword. The sintax for Getmem is: Getmem (pointer, size); So, you grab the memory you need. Then, as you are working with pointers, instead of refering to the variables as A[10,10], you refer as A^[10,10]. Easy, isn't it ?... Next, in the end of the program (or when you want to free the memory for another pointer or something like that), you use the Freemem keyword. The sintax is: Freemem (pointer, size); You must de-allocate as much memory as you allocate, under the penalty of losing that memory. The problem with working with pointers is that if you don't de-allocate them, after a couple of program execution, you'll get an 'Out of Memory' error, because the memory is already filled with pointers. So, never forget to de-allocate the pointers. As you can see, this method of using pointers is very easy to use and implement. The other methods (the dynamic ones) are ten times more complicated, and in the majoraty of cases, this is better, especially for games and demos, because everything in them is planned. Keep one thing in mind, tough. Because of the way PC's work, you can not allocate more than 64Kb to just one pointer. This has to do with segmentation, but there are ways to turn this around. One more thing, in the lines with Getmem and Freemem I use a function, called sizeof, whose sintax is: =sizeof(structure); This function returns the size in bytes of the structure in parentesis. ■ Points of view Although this article is called Points of View, it has nothing to do with oppinion. This is like the conclusion of the magazine. I just called that because I will sometimes expose my distorted points of view here, and I didn't wanted to call this 'Conclusion'... It would sound vulgar. So, what will I see here? I don't really know. After all, this is the first issue. I don't have nothing to say. I'll wait until I read/hear some remarks about 'The Mag', and then I'll write something, like a response or an apologie request. As I talked about apologies, I will take the chance to ask one or two. I apologize for the English in this magazine, but you must understand three things: 1. I'm not English 2. It's bloody hard keeping a good thinking without worring about the the grammar, left alone if I cared. 3. I write very fast (compared to the other persons), and at that speed it's very hard not to make mistakes. I also apologize about my language and the whole tone of the magazine. In this case, you must notice I don't get any money for doing this, so I must do it for fun. Well, there's only one thing left in my magazine... ■ The adventures of Spellcaster, the rebel programmer of the year 2018. Episode 1 - The beggining I remember it all... From the day it started my trail of misery... And I think I'll never forget it. It was a friday night, the 26th September 2018. I was just trying to program my new computer I got by my 18th birthday, just 23 days from then. It was a top of line Octium, clocked at 33 Gigahertz, with 10 Gigabytes RAM, a hard drive with 800 Gigabytes hard drive and a whole lot more stuff. Just what I always wanted. As I said, I was programming my computer, a simple strategy game in Pascal v18.2, when suddently, my computer ran dead. It wouldn't do nothing. It just froze up. I tried rebooting it, then I turned the power off and on, and nothing would happen. In panic, I rushed to the phone, and I started dialing the number of COMPTEL, the largest manufacturer of computers, programs and other assorted things. It also fixed computers. They said they were on the way. I sat down, a bit more relaxed and started to think about COMPTEL, from it's founding by some guy called Bill something to their takeover of the world. I was disturbed from my toughts by a siren. I look out the window, and there it was... A white van with the words 'COMPTEL' writen in red on the side. They knocked at my door. I opened the door, and two persons entered. They were exactly alike, quite tall, brown hair, glasses and bad breath. As I live in the age of clones, I wasn't surprised. I showed them the computer and they told me to leave. So I did. Minutes later, they called me. I entered my room, anxious. They weren't looking happy, but I didn't cared. All I cared was my computer. I looked at it, and the green letters the screen displayed just made my fears away. - Thank you very much... - I said, with a big smile. - Mr. Andrade... As we always do after a repair, we scan the disk for pirated software, subversive campaign against COMPTEL, that kind of things. - What do you mean ?... I don't have any of those. - Yes, that is true. - said the other man. - You have very little software instaled in your hard drive indeed. - But we've noticed a very serious fellony... - Can you tell us, Mr.Andrade, why isn't Windows 2018 installed ? - Because I don't have any use for it... I am a programmer, not a user. I pratically I only use MY-DOS, v6.0. - I answered, my heart going faster. - How can you program without Windows ? - one of them asked, angry. - Without Visual Basic ? - asked the other, with a yellow smile. - Yes... - I answeared, nervously. - I use Turbo Pascal... With assembler. - Do you know article 52421/52 of COMPTEL law, Mr.Andrade ? - N-n-n-no I don't. - I began to sweat. - The article states that no operating sistem besides Windows 2018 can be used... The article also says that no programming language, other than Visual Basic, can be used. - But...but... I'm a programmer. Windows and Visual Basic aren't made for programmers... - Tough luck... - said one of the COMPTEL men, as a third man grabed me from behind, dragging me to the van, while my parents looked as I was beeing taken away. A week after, I was in court, before The Judge himself... Bill Gates Jr. - How do you plea to this charges ? - Not guilty, sir... - Ha, ha, ha !!! - the whole room laughed, as The Judge hitted the table with his hammer. - Diogo de Andrade, I found you guilty of violating the article 52421/52, usage of illegal software. The sentence will be 30 years incarceration, with no possibility of parole. The sentence will be carried out in the Atari World Penetenciary... - No, no... - I screamed. - Everything but the Atari Penetenciary. The judge laughed at my plea, and ignored it. Now, these walls is all I have left. I am here at almost a month now, with no computers to program, except for Ataris... Cruel faith is mine. Beeing doomed to 30 years of this suffering. Unless, of course, I can escape... See you in the next issue Diogo "SpellCaster" Andrade