From baxtrom@home.com Sun Feb 04 17:52:41 2001 Complete repost of these files: Sunday, February 11, 2000 Someone e-mail me and remind me. :) Lesson 1: The basics of C++ I am writing this for those people who want to learn how to program in C++, especially those who had trouble. It is for those of you who want a sense of accomplishment every time your program works perfectly. If you want the sense of accomplishment, read on. C++ is a programming language. It is a programming language of many different dialects, just like each language that is spoken has many dialects. In C though, they are not because the "speakers" live in the North, South, or grew up in some other place, it is because there are so many compilers. There are about four major ones: Borland C++, Microsoft Visual C++, Watcom C/386, and DJGPP. You can download DJGPP http://www.delorie.com/djgpp/ or you may already have another compiler. Each of these compilers is a little different. The library functions of one will have all of the standard C++ functions, but they will also have other functions or, continuing the analogy, words. At times, this can lead to confusion, as certain programs will only run under certain compilers, though I do not believe this to be the case with the programs in these tutorials. +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ If you don't have a compiler, I strongly suggest you get one. A simple one is good enough for my tutorials, but get one. +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ C++ is a different breed of programming language. It has only a few keywords for DOS, and it has no keywords to use for output. This means that almost everything is stored in a header file. This gives the use of many functions. But lets see a real program... #include int main() { cout<<"HEY, you, I'm alive! Oh, and Hello World!"; return 0; } That does not look too hard, right? Lets break down the program and then look at it. The #include is a preprocessor directive which tells the compiler to put code in the header file iostream.h into our program! By including header files, you ~can gain access to many different functions. For example, the cout function requires iostream.h. The next thing is int main() what this is saying is that there is a function called main, and that it returns an integer, hence int. Then those little braces ( { and } ) are used to signal the beginning and ending of functions, as well as other code blocks. If you have programmed in Pascal, you will know them as BEGIN and END. The next line of the program may seem strange. If you have programmed in other languages you might think that print would be used to display text. However, in C++ the cout function is used to display text. It uses the << symbols, known as insertion operators. The quotes tell the compiler that you want to output the literal string as-is. The ; is added to the end of all function calls in C++. The penultimate line of code is ordering main to return 0. When one returns a value to main, it is passed on to the operating system. As a note, declaring int main() or void main() both will generally work. It is accepted practice to some to declare main as a void, but to others it is extremely upsetting. Previously, these tutorials had used void main, however, this is NO LONGER recommended, as it does not conform to the ANSI standard. After, the brace closes off the function. You can try out this program if you want, just cut and paste it into the IDE of a compiler such as DJGPP, or save it to a file ending with a .cpp extension, and use a command-line compiler to compile and link it. Comments are extremely important to understand. When you declare that an area is a comment, the compiler will IGNORE it. To comment it is possible to use either // , which declares that the entire line past that point is a comment, or it is possible to use /* and then */ to block off everything between the two as a comment. Certain compilers will change the color of a commented area, but some will not. Be certain not accidently declare part of your code a comment. Note that this is what is known as "commenting-out" a section of code, and it is useful when you are debugging. So far you should be able to write a simple program to display information typed in by you, the programmer. However, it is also possible for your program to accept input. the function you use is known as cin>>. Wait! Before you can receive input you must have a place to store input! In programming, these locations where input and other forms of data are stored, are called variables. There are a few different types of variables, which must be stated. The basic types are char, int, and float. Char is used to create variables that store characters, int is used to create variables that store integers (numbers such as 1, 2, 0, -3, 44, -44), and float is used to delare numbers with decimal places. In fact, they are all keywords that are used in front of variable names to tell the compiler that you have created a variable. That is known as "declaring a variable". When you declare a variable, or variables, you must end the line with a semi-colon, the same as if you were to call a function. If you do not declare the variable you are attempting to use, you will receive numerous error messages and the program will not run. Here are some examples of declaring variables: int x; int a, b, c, d; char letter; float the_float; It is not possible, however, to declare two variables of different types with the same name. #include int main() { int thisisanumber; cout<<"Please enter a number:"; cin>>thisisanumber; cout<<"You entered: "<> sets the value of thisisanumber to be whatever the user types into the program when prompted. Keep in mind that the variable was declared an integer, which means the output will be in the form of an integer. Try typing in a sequence of charaters, or a decimal when you run the example program to see what you get as a response. Notice that when printing out a variable, there are not any quotation marks. If there were quotation marks, the output would be "You Entered: thisisanumber." Do not be confused by the inclusion of two separate insertion operators on a line. It is allowable, as long as you make certain to have each separate output of variable or string with its own insertion operator. Do not try to put two variables together with only one << because it will give you an error message. Do not forget to end functions and declarations with the semi-colon(;). Otherwise you will get an error message when you try to compile the program. Now that you know a little bit about variables, here are some ways to manipulate them. *, -, +, /, =, ==, >, < are all operators used on numbers, these are the simple ones. The * multiplies, the - subtracts, and the + adds. Of course, the most important for changing variables is the equal sign. In some languages, = checks if one side is equal to the other side, but in C++ == is used for that task. However, the equal sign is still extremely useful. It sets the left side of the equal sign, which must be one AND ONLY one variable, equal to the right side. The right side of the equal sign is where the other operators can be used. Here are a few examples: a=4*6; //(Note use of comments and of semi-colon) a is 24 a=a+5; // a equals the original value of a with five additional units a==5 //Does NOT assign five to a. Rather, it checks to see if a equals 5. The other form of equal, ==, is not a way to assign a value to a variable. Rather, it checks to see if the variables are equal. It is useful in other areas of C++ such as if statements and loops. You can probably guess what the < and > are for. They are greater than and less than checks. For example: a<5 //Checks to see if a is less than five a>5 //Checks to see if a is greater than five a==5 //Checks to see if a equals five, for good measure --- Note: My homepage is http://www.cprogramming.com. My email is webmaster@cprogramming.com. Please email me with comments and or suggestions. If you want to use this on your own site please email me and add a link to http://www.cprogramming.com. Thanks :) Learning C: lesson 2 Hello, this is Alexander. Since I finally got an email from someone who liked my previous lesson, I am going to make the second installment. This one will be about variables, and stuff like 'if' statements. 'IF' is the most important word in programming for many programs. Without it there is no conditional statements. This means that there can be only one way a program can execute. It would almost impossible to make a program without this one simple word. There are many things to understand when using IF statements. First, you must understand stuff like OR NOT etc. This are the most important, so I will describe how to use them in C and C++ programming below: (NOTE: ZERO IS FALSE! ONE IS TRUE!) NOT: This just says that the program should reverse the value...for example NOT(1) would be 0. NOT(0) would be 1. NOT(any number but zero) would be 0. In C and C++ NOT is written as - ! - just one simple little character. It is very useful and can save lots of time. AND: This is another important command, and it is used to say that if this AND this is true... for example (1)AND(0) would come out as 0. (1)AND(1) would come out as 1. (ANY REAL NUMBER BUT ZERO)AND(0) would be 0. (ANY REAL NUMBER BUT ZERO)AND(ANY REAL NUMBER BUT ZERO) would be 1. The AND is written as - && - in C++. It is just two simple characters. OR: Very useful is the OR statement! For example (1)OR(0) would be 1! (0)OR(0) would be 0. (ANY REAL NUMBER)OR(ANY REAL NUMBER BUT ZERO) would be 1! It is simple, either one can be true and make the whole thing true. The OR is written as - || - in C++. It is also two simple characters. The next thing to learn is to combine them... What is !(1 && 0)? Of course, it would be 1. This is because 1 && 0 evaluates two 0 and ! 0 equals 1. Try some of these...they are not hard. If you have questions about them, you can email me at lallain@concentric.net. A. !(1 || 0) ANSWER: 0 B. !(1 || 1 && 0) ANSWER: 0 (AND is evaluated before OR) C. !((1 || 0) && 0) ANSWER: 1 (Parenthesis are useful) If you find you enjoy this you might want to look more at Boolean Algebra, which is also very helpful to programmers as it can be good for helping program conditional statements. IF is used like this IF(TRUE) { DO WHAT IS IN THE BRACKETS } ELSE is basically ELSE { DO WHAT IS IN THE BRACKETS } Let's look at a simple program for you to try out on your own... #include //For output #include //For getch() void main() //Most important part of the program! { int age; //Need a variable... cout<<"Please input your age: "; //Asks for age cin>>age; //The input is put in age if(age<100) //If the age is less than 100 { cout<<"You are pretty young!"; //Just to show you the output } if(age==100) //Remember, if the age equals 100 needs two = { cout<<"You are old"; //Just to show you it works... } if(age>100) { cout<<"You are really old"; //Proof that it works for all conditions } } Now, this program did not use && || ! or anything in it. This is because it didn't need too. I think you should probably be able to make your own if statements with them without having to worry too much about problems. As always, you can email me at lallain@concentric.net Note: My homepage is http://www.cprogramming.com. My email is lallain@concentric.net. Please email me with comments and or suggestions. If you want to use this on your own site please email me and add a link to http://www.cprogramming.com. Thanks :) Lesson 3: Loops This is the third installment of the Lessons in C programming tutorials created by me, Alexander. In this lesson I will cover loops. Loops basically do what it sounds like, loop. If you have read lesson 2 you should understand some Boolean expressions. If you do not, you should read it again. When working with loops it is important to understand truth and false. Maybe you should try doing some truth tables with problems. There are basically 3 types of loops. FOR, WHILE, DO WHILE Each of them has their uses. They are all outlined below. FOR - FOR loops are the most useful type, I believe. The layout is for(variable initialization, conditional, incrementing variable) It is very versatile, and the layout can be changed somewhat. Basically, the variable initialization allows you to either declare a variable and give it a value, or give a value to another variable. Second, the conditional statement. What it does is it says that while the conditional is true then it would do what in is in the body. Third, the incrementing variable section. It does not have to increment a variable. It can decrement, which is subtracting one, or it can perform various other manipulations on the variable. Ex. #include //We only need one header file void main() //We always need this { //The loop goes while x<100, and x has one for(int x=0;x<100;x++)/*THE LOOP*/ //added to it every time the loops { cout< //We only need this header file void main() //Of course... { int x=0; //Don't forget to declare variables while(x<100) //While x is less than 100 do { cout< int main() { int x=0; do while(x<100) { cout << x << endl; x++; } } Note: My homepage is http://www.cprogramming.com. My email is lallain@concentric.net. Please email me with comments and or suggestions. If you want to use this on your own site please email me and add a link to http://www.cprogramming.com. Thanks :) Lesson 4: Functions Now that you have learned all about variables, loops, and if statements it is time to learn the next thing in programming: Functions. Obviously, you should have a good idea about what a function is, as you have used ones like cout before. However, this lesson will be more in detail about not only functions that are already made, but about making your own, or maybe I will continue this later... A good way to describe a function is to show its prototype. That means, what it should return, and what it should take as an argument. For example, the prototype of getch() is... int getch(void); The int means that it returns an integer, the void means that it does not take an argument. Now, you may know that getch returns a character! However, that does not mean it must return a character. The fact that the return type is an integer makes no difference, because the ASCII character set does not care what type of number it is, as long as it is a number...don't worry if you don't understand, it is not too important right now. What is important is that you understand prototypes. Another prototype is... int kbhit(void); It returns an integer, and it takes no value. Now that I hope you understand this then you will be able to use the help files much more easily, and I can go into more about functions. First, what functions are useful. There are many useful functions, and often they are hard to find. For Turbo C++ Lite some useful functions include, but are no limited to: cout<< iostream.h output cin>> iostream.h input int getch(void) conio.h get characters void clrscr(void) conio.h clear screen Okay, you might be thinking that this is nothing! Four measly functions, and you are right! If there were only a few functions then C/C++ would not be useful. However, a lot of programs do not need all that many functions. Of course, I suggest that you know ever function that you can, or at least the name. For this purpose, I will be posting an entire listing of ever function that I can find out of either help or books I have read. However, for now, these are probably the most useful functions. After all, if you can clear the screen, get input and output, and get keypresses, which are useful for stopping the program from immediately going back to the IDE you can do quite a bit! Believe me, there are a few specialized, but very useful functions, the thing is, you don't really need to use them all the time! If you have a problem with a function that you need, and I have not put up my list yet, then email me at lallain@concentric.net, and I will find you what you need! Anyway, after that long spiel on not needing a lot of functions, I am going to show you how to make your own functions! Wow, I can do that? Of course, otherwise C/C++ would not be useful! So, prepare to learn how to make functions. First let me give you an entire example program. Then we will look at it, and learn how to make our own programs. #include #include int mult(int x, int y); void main() { int x, y; cout<<"Input a number, and what number to multiply it by"; cin>>x>>y; cout< void function(void); void main() { function(); } void function(void) { cout<<"This is a useless and totally wasteful function"; } What is does is declare that there is going to be a function, by prototyping, and then at the bottom the function is defined, and it only does one thing...outputs "This is a useless and totally wasteful function" However, what if you wanted to do something that took 3 lines four hundred times in different places? Say, #include void function(void); void main() { LOTS OF CODE THAT NEEDS TO OUTPUT Line 1Line 2Line 3 } void function(void) { cout<<"Line 1"; cout<<"Line 2"; cout<<"Line 3"; } That, aside from the fact that it is a bad example, is where you would use it. When you need to call something a lot of times, but don't want to cut and paste. Functions are very useful, and I hope I explained them well enough for you to understand. Note: My homepage is http://www.cprogramming.com. My email is lallain@concentric.net. Please email me with comments and or suggestions. If you want to use this on your own site please email me and add a link to http://www.cprogramming.com. Thanks :) Lesson 5: switch...case I know that this is probably a let-down, after you learned all about functions, but switch...case is important to know. After all, it can save space with if statements, and it is useful. Besides, I couldn't think of anything else that I wanted to write about. Switch...case looks like this: switch(expression or variable) { case it equals this: do this; break; case it equals this: do this; break; case it equals this: do this; break; ... default do this } So, it works like this. The expression or variable has a value. The case says that if it has the value of whatever is after this case then do whatever follows the colon. The break says to break out of the case statements. Break is a keyword that breaks out of the code-block, surrounded by braces, that it is in. So unless you want it to try the next case then use break. --You can also use it to break out of loops, something that I failed to mention at the time.-- What is it used for, the switch...case? Well, let's say that you are writing a menu program, then you would want to process some input, right? Well, you would want to use a switch...case statement to process more than one input, because it is more easily used than if statements. Here is an example program: #include #include void main() { char input; cout<<"1. Play game"; cout<<"2. Load game"; cout<<"3. Play multiplayer"; cout<<"4. Exit"; input=getch(); //Remember I said you don't need many functions... switch(input) { case 1: playgame(); break; case 2: loadgame(); break; case 3: //Note use of : not ; playmultiplayer(); break; case 4: break; default: cout<<"Error, bad input, quitting"; } } If you are not understand this, then try putting in if statements for the case statements. Also, the reason exit works with a break is that after you break out of the switch statement then it would be the end of the program. The same thing would be for default. If you don't like that, then make a loop around the whole thing. I know I did not prototype the functions, but it was a very simple example. You could easily make a few small functions. Note: My homepage is http://www.cprogramming.com. My email is lallain@concentric.net. Please email me with comments and or suggestions. If you want to use this on your own site please email me and add a link to http://www.cprogramming.com. Thanks :) Lesson 6: An introduction to pointers Welcome to the sixth in my series of tutorials. This is one about a topic that you may or may not have already heard about...pointers. What are they, what do they do, why do we care? First, why do we care. We care about pointers because they allow access to memory, the also make array-access faster, they are also somewhat necessary to understand some functions. Most importantly, you will see them a lot in other people's code. You may not need to use them much, but it will be tremendously important to understand them. Second, what do they do. Well, I might as well address this issue as well as what they are at the same time. Pointers are what they sound like...pointers. They point to locations in memory. Picture this: a big jar that holds one thing, the name of another jar. In the other jar is the value of an integer. The jars are memory locations. The jar that holds the name of the other jar is a pointer. It points to the other drawer. How can you use this? Well, look at this little piece of code: #include void main() { int x; int *pointer; pointer=&x; cin>>x; cout<<*pointer; } Guess what! The cout outputs the value in x. Why is that? Well, look at the code. The integer is called x. Then a pointer to an integer is defined as pointer. The astrick(*) symbol means that it is a pointer. Then I give the memory location of x to pointer by using the ampersand(&) symbol. It gives the memory location of the variable it is in front of. For example, if the jar that had an integer had a ampersand in it it would output its name, or location. Then the user inputs the value for x. Then the cout uses the * to put the value stored in the memory location of pointer. Huh? Picture the jars again. If the jar with the name of the other jar in it had a * in front of it it would give the value stored in the jar with the same name as the one in the jar with the name. It's not too hard, the * gives the value in the location. The unastricked gives the memory location. I hope this has been at least an interesting introduction to pointers. I do not suggest that you play around with them too much as you can do unpleasant things on your computer, but you now should have a better understand of what they are. Note: My homepage is http://www.cprogramming.com. My email is lallain@concentric.net. Please email me with comments and or suggestions. If you want to use this on your own site please email me and add a link to http://www.cprogramming.com. Thanks :) Lesson 7: Structures Welcome to the seventh lesson. This is my first lesson that I will explain classes. However, I will explain more about structures, because they can be useful, and they are a good way to get a feel for how a class works. What are structures? They are a way to store more than one data-type under the same name. Fore example: #include //For strcpy struct database { int age; char name[20]; float salary; }; void main() { database employee; employee.age=22; strcpy(employee.name, "Joe"); employee.salary=12000.21; } Don't worry about the name[20]. That is just an array. It can hold more than one character all called under the same name. They are used like strings. I will do my next lesson on arrays, I promise, because they are very important. The struct database declares that database has three variables in it, age, name, and salary. Eventually, you can use database like a variable type like int. You can create an employee with the database type like I did above. Then, to modify it you call everything with the employee. in front of it. You can also return structures from functions by defining their return type as a structure type. Example: struct database fn(); You can make arrays of structures as well. I will show you how to do this in lesson 8. That will be up in a few days. I suppose I should explain unions a little bit. They are like structures except that all the variables share the same memory. When a union is declared the compiler allocates enough memory for the largest data-type in the union. To access the union you use the . like in structures. Also, if you are accessing the union of structure through a pointer use the -> operator. for example, database->employee . The most useful thing about unions is that you can manipulate the bytes of the data-types. You might want to see what you can do if you understand that sort of stuff. Personally, I have never used a union. Note: My homepage is http://www.cprogramming.com. My email is lallain@concentric.net. Please email me with comments and or suggestions. If you want to use this on your own site please email me and add a link to http://www.cprogramming.com. Thanks :) Lesson 8: Array basics This is the eight installment of my lessons, and it is on arrays. Arrays are essentially a way to store many values under the same name. You can make an array out of any data-type, including structures. For example, you could say int examplearray[100]; //This declares an array This would make an integer array with 100 slots, or places to store values. The only difficult thing is that it starts off with the first index-number, that is, the number that you put in the brackets to access a certain element, is zero, not one! Think about arrays like this: [][][][][][] Each of the slots is a slot in the array, and you can put information into each one of them. It is like a group of variables side by side almost. What can you do with this simple knowledge? Lets say you want to store a string, since C++ has no built-in datatype for strings, in DOS, you can make an array of characters. For example: char astring[100]; Will allow you to declare a char array of 100 elements, or slots. Then you could get it from the user, and if the user types in a long string, it will all go in the array. The neat thing is that it is very easy to work with strings in this way, and there is even a header file called STRING.H. I will have a lesson in the future on the functions in string.h, but for now, lets concentrate on arrays. The most useful aspect of arrays is multidimensional arrays. For example: int twodimensionalarray[8][8]; Think about multidimensional arrays: [][][][][] [][][][][] [][][][][] [][][][][] [][][][][] This is a graphic of what a two-dimensional array looks like when I visualize it. declares an array that has two dimensions. Think of it as a chessboard. You can easily use this to store information about some kind of game, or write something like tic-tac-toe. To access it, all you need are two variables, one that goes in the first slot, one that goes in the slot. You can even make a three dimensional array, though you probably won't need to. In fact, you could make a four-hundred dimensional array. It is just is very confusing to visualize. Now, arrays are basically treated like any other variable. You can modify one value in it by putting: arrayname[arrayindexnumber]=whatever; You will find lots of useful things to do with arrays, from store information about certain things under one name, to making games like tic-tac-toe. One little tip I have is that you use for loops to access arrays. It is easy: #include void main() { int x, y, anarray[8][8];//declares an array like a chessboard for(x=0; x<8; x++) { for(y=0; y<8; y++) { anarray[x][y]=0;//sets all members to zero once loops is done } } for(x=0; x<8;x++) { for(y=0; y<8; y++) { cout<<"anarray["<> then it won't work! It terminates at the first space. However, you can use the function gets(char *s);