Learning C: lesson I
Hello, this is Alexander.  I am writing this for those people who want to learn how to
program in C, but are scared of it.  It is scary, but it is not hard, well, it is hard, but
it is a great feeling making a game, or a program of no value, but knowing that YOU made
it.  This is for the same reason that I code my own HTML, even with so many different ways
to use a editor.  I like to know that I made it, that I didn't just say what I wanted. If
you want this sense of accomplishment, then read on.

C is a programming language, of course.  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 from one of the
pages connected to my site<http://www.concentric.net/~lallain> and go to the programming
part, or you may have another compiler.  I also hope to upload the shareware version of
Turbo C++, which is very similar to Borland C++.

Each of these compilers is a little different.  The library functions of one will have all
of ANSI C, the standard, but will have many other functions, or to continue my analogy,
'words'.  What I am getting at is that some of the stuff I use in this may have to be
changed.  If I say #include "malloc.h", you have need to say #include "alloc.h".  It is
because there are so many different ways of 'saying' something that sometimes it is hard to
communicate, take a Southerner, and a Northerner.  There are often words that get confused.

So, anyway, if you don't have a compiler, I strongly suggest you get one, a simple one is
good enough for my lessons, if they are worthy of that title ;), but get one.  

C is a different breed of programming.  It has only 33 keywords for DOS, and it has no
keywords to use for output.  This means that almost everything is stored in a -header
file-(note: all terms of interest will be set off, but I can't bold).  This gives the use
of many functions.  But lets see a real program...


#include <iostream.h>

void main()
{
        cout<<"HEY, you, I'm alive!";
}

So, that sure looks easy doesn't it.  Some of the stuff is weird.  Okay, lets break it down. 
The -#include- is a preprocessor directive, one that tells the compiler to put all the stuff in
the header file -iostream.h- into our program!  This allows me to use some functions later on. 
Also, for most header files you can also use " " to surround the name instead of <>.

The next thing is -void main()- what this is saying is that I am going to have a function
called -main-, and that it returns no value, hence -void-.  Then those little -{- braces
are used.  They are like the BEGIN and END commands of pascal.  basically they are used to
define aresa of some function, or other things we will learn of later.  
The next thing is strange.  If you have programmed in other languages you might think that
print would be used to display text.  It can be, but only if you use a function called
-printf("text goes here");- the cout command can be used to display text but it needs those
strange << things known as insertion operators, basically use it to put text on the screen. 
The quotes tell it to put the string as-is on the screen.  After that, the little -;- is
used to tell it that that is the end of that function.
        
After, the braces close off the function.  Pretty simple, eh?  You can try out this program
if you want, just cut and paste it.
You should also know comments.  To comment you can either use // which goes to the end of
the line, or you can sue the /* and then */ to make a comment.  This is useful.  Make sure
that you know how to use it, or you might accidentally comment out a huge chunk of code!
        
You may be thinking by now that that is fine and good, but what If I want INPUT!?  That is
pretty easy.  Remember cout<<?  Just use cin>>.  This simply is used to get input.  
        

#include <iostream.h>
void main()
{
int thisisanumber;
cout<<"Please enter a number:";
cin>>thisisanumber;
cout<<thisisanumber;
}

Okay, what does this do?  It does all that you want.  It gets input.  We know most of it.  The
only tough stuff is the cin>> and int.  int is basically a keyword that declares a variable to
be an integer.  Other types include char, unsigned char, float, long, double.  These define
characters, floating point decimals, long integers, and double floats, which go out farther. 
These will be used in other programs.  The cin>> basically says that it should put in
thisisanumber whatever the user types in.  If it is not a number, the next output will be kind
of weird.  Then cout<< uses no quotes to print a variable, this means to print a variable, if
it was as-is in quotes then it would print on the screen a string "thisisanumber".  Don't
forget to end functions and declarations with the semi-color(;).  Otherwise you will get an
error.  They can be very tough to track down too.
Now is about the time to learn something about variables.  I have talked about declaring
them, but what good is that if you don't know how to use them.  Here goes:
        
*, -, +, /, =, ==, are all operators used on numbers, these are the simple ones, if you
want ore info on any of this, by the way, e-mail me at lallain@concentric.net.  The *
multiplies, the - subtracts, the +( adds, the = assigns the value on the right to the one
on the left: a=3 means that 3 will slide over to be the value stored in a.  The == is a
comparison checker.  
a=3;
a==3;

This gives a the value of 3, and then sees if it has the value of three.  This could be use in
an if statement.  DONT FORGET TO DECLARE VARIABLES.  two otehr things used as comparisons are
the < and > they do what they do in school check to see if it is great than or less than.  To
see something like greater or equal too then use >=.  This is useful in some stuff I will cover
next week.  

                                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 <iostream.h>                   //For output
#include <conio.h>                      //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

                                       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 <iostream.h>  //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<<x<<endl;           //Outputting x
              }                         
            }

This program is a very simple example of a for loop.  x is set to zero, while x is less
than 100 do cout<<x<<endl; add 1 to x until the loop ends.  Pretty simple to understand,
but it is a very powerful loop, and much better than WHILE and DO WHILE loops.

WHILE - WHILE loops are very simple, but not as useful as FOR loops.  The basic structure
is...WHILE(true) then do whatever is in the body.  The truth could be x==1 or while(x!=7)
(x does not equal 7)

        Ex. #include <iostream.h> //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<<x<<endl;        //Same output as the above loop 
                  x++;          //Adds 1 to x every time it repeats 
                  } 
                }

This was another pretty simple example, but it is longer than the above FOR loop, showing
why I like for better than while, though while is a very easy loop to use, so if you are
having trouble then you can use it, but try to use for.

DO WHILE - DO WHILE loops are useful for only things that want to loop at least once.
          basically it goes DO { THIS } WHILE(TRUE)

Now, it is your turn to try and do a loop!  make a DO WHILE loop that does what the above
programs do...output 0 to 99!  It is not hard, if you have trouble email me at
lallain@concentric.net and I will give you some help... Best of luck :)  Check back again for
more programming in C!

                                        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 funcitons, 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 <iostream.h>
#include <conio.h>

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<<endl<<mult(x, y);
  getch();
}

int mult(int x, int y)
{
  return x*y;
}

How is this useful...Well, in this program the function is totally useless, and it can only
multiply integers!  But this is just to show you how to make functions, after you
understand the basics I hope you will be able to do anything yourself.

What my example does: #includes...basic includes What is int mult(int x, int y); ?  That is
a prototype of the function, without it you would not be able to use mult! What
is void main()?  You should know that. What is cout<<endl<<mult(x,y);  Well, basically it
puts us down a line, and then it outputs what mult returns.  More on this later. What is
        
        int mult(int x, int y) 
        { 
          return x*y; 
        }
        
Well, it is a function!  It says that the return type is an integer. When the keywork
return is used it says that the function mult has a value of whatever x*y would be...as it
says return x*y.  The two ints that it takes are x and y.  So it multiplies     them and returns 
that value.  Then outputs mult(x, y);  It is perfectly legal.  Perhaps it would help if you 
think of it as saying that the function mult has a value of whatever x*y is.  This is not
true really, it just returns that value, and you can do whatever you want with it, but I
hope it helps.

What can you do?  You can make void functions that do anything...

#include <iostream.h>

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 <iostream.h>

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. 

                                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 <iostream.h>
        #include <conio.h>
        
        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.

                                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 <iostream.h>

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.

                                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:

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.

                                        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 <iostream.h>

void main()
{
  int x, y, anarray[8][8];//declares an array like a chessboard
  for(x=0; x<9; x++)
  {
    for(y=0; y<9; y++)
    {
      anarray[x][y]=0;//sets all members to zero once loops is done
    }
  }
  for(x=0; x<9;x++)
  {
    for(y=0; y<9; y++)
    {
      cout<<"anarray["<<x<<"]["<<y<<"]="<<anarray[x][y];//you'll see
    } 
  }
}

Here you see that the loops work well because they increment the variable for you, and you only
need to increment by one.  It is simple, and you access the entire array, would you want to use
while loops?

                                        Lesson 9: Strings
                                        
        This lesson is one on strings.  Strings are really arrays, but there are some different 
functions that are used for strings, like adding to strings, finding the length of strings, and
also of checking to see if strings match.  Strings are basically sentences, or words.  Like, 
"This is a string".

        Strings are basically character arrays.  For example, to declare a string of 50 letters, you
would want to say:

char string[50];

This would declare a string with a length of 50 characters.  Don't forget that arrays begin at 
0, not 1 for the index-number.  Also, a string ends with a null character, literally a '/0' 
character.  But, just remember that there will be an extra character on the end on a string.  It
is like a period at the end of a sentence, it is not counted as a letter, but it still takes up
a space.

What are strings useful for?  Well, for one thing, you might want to get a person's name.  If you
wanted to, you would need a string, because a name can't fit in one variable!  It is, however, a
collection of characters, and so fits nicely into a character array.  

Now, what if you want to input a string?  Well, if you try to use cin>> then it won't work!  It
terminates at the first space.  However, you can use the function gets(char *s);
.

Gets is basically a function that reads in a string and stops reading at the first new-line, for 
example, when a user hits enter.  Gets is in stdio.h. All you do, is put the name of the array and it will work out,
because the pointer char *s is basically one way you tell a function that you will be passing an
array, although it is a pointer, it is still the string you give.  Essentially, char *s points to
a string, and you can access this string just like an array.  

I will touch upon this relationship as described above in another lesson that will be a more 
advanced lesson on pointers and arrays.  

Anyway, to get a string from a user you want to use gets.  An example program of this would be:

#include <stdio.h>                //For gets
#include <iostream.h>             //For all other input/output functions


void main()
{
 
  char astring[50];               //This declares a character array that can be used as a string
 
  cout<<"Please enter a string";  //You should know this one! 
  gets(astring);                  //The user will input a string(with spaces)
 
  cout<<"You input: "<<endl;      //You know this one too!
  cout<<astring;                  //This is how you output character arrays, but not others!

}

Ok, thats pretty simple.  But, what if you want to use some of the nifty functions from string.h?

Well, these include the following functions:

int strcmp(const char *s1, const char *s2);

strcmp will accept two strings.  It will return an integer.  This integer will either be:
Negative if s1 is less than s2.
Zero if s1 and s2 are equal.
Positive if s1 is greater than s2.

Strcmp is case sensitive.


int strcmpi(const char *s1, const char *s2);

strcmp will accept two strings.  It will return an integer.  This integer will either be:
Negative if s1 is less than s2.
Zero if the s1 and s2 are equal.
Positive if s1 is greater than s2.

Strcmpi is not case sensitive, if the words are capitalized it doesn't matter.

char *strcat(char *desc, char *src);

strcat is short for string cacatenate, which means to add to the end, or append.  It does just this,
the first string is what the second string is stuck on the end of.  It basically returns the 
cacatenated string.  The first string will also have the entire string added to it.

char *strupr(char *s);

strupr converts a string to uppercase.  It also returns a string, which will all be in uppercase.
The input string, if it is an array, will also all be uppercase.

char *strlwr(char *s);

strlwr converts a string to lowercase.  It also returns a string, which will all be in uppercase.
The input string, if it is an array, will also all be uppercase.

size_t strlen(const char *s);

strlen will return the length of a string, minus the termating character(/0).  The size_t is 
nothing to worry about.  Just treat it as an integer.

Some of the stuff in the strings may be confusing.  The const char *s stuff, for example.  But,
just remember that basically all of that will be a string!  It doesn't matter what the code is
right now, just what the functions do.

Now, a small program using many of the string functions!

#include <iostream.h>   //For cout
#include <string.h>     //For many of the string functions
#include <stdio.h>      //For gets

void main()
{
  
  char name[50];            //Declare variables
  char lastname[50];        //This could have been declared on the last line...
  cout<<"Please enter your name: ";   //Tell the user what to do
  gets(name);             //Use gets to input strings with spaces or just to get strings after the user presses enter
  
  if(!strcmpi("Alexander", name))  //The ! means not, strcmpi returns 0 for equal strings
  {                                  //strcmpi is not case sensitive
    cout<<"That's my name too."<<endl; //Tell the user if its my name
  }
  else                              //else is used to keep it from always outputting cout<<"That's not my name."
  {
    cout<<"That's not my name."<<endl;
  }
  
  cout<<"What is your name in uppercase..."<<endl; 
  strupr(name);                   //strupr converts the string to uppercase
  cout<<name<<endl;               
  cout<<"And, your name in lowercase..."<<endl;
  strlwr(name);                    //strlwr converts the string to lowercase
  cout<<name<<endl;
  cout<<"Your name is "<<strlen(name)<<" letters long"<<endl;  //strlen returns the length of the string
  cout<<"Enter your last name:";
  gets(lastname);                    //lastname is also a string
  strcat(name, " ");                            //We want to space the two names apart
  strcat(name, lastname);           //Now we put them together,we a space in the middle
  cout<<"Your full name is "<<name; //Outputting it all...
}

                                                        Lesson 10: File I/O(part 1)
        This is a slightly more advanced topic than what I have covered so far, but I think that it 
is useful, and I think it will be useful to many people.  File i/o is basically reading, and
writing files.  This lesson will only cover text files, that is, files that are readable
through a text editor, as opposed to binary files(exes for example).  It will not cover a great
deal, for example, this lesson will not deal with searching files or reading specific data from
files.  It will merely be concerned with opening, writing, and reading text files.  Don't worry
though, lesson 11 will cover much more on this topic.
        Well, how does it all start anyway?  Files have their own specific functions to use, as 
well as their own data-type, called a FILE(There is more to this, but right not it is not
important, and it will be explained later, when it is useful).  The way to use the FILE type is
the same way as using an integer, or a float, or a char:

FILE *newfile; //Creates a FILE called newfile(don't forget that it is a pointer)

        Now, we can't use this unless there is a way to give the FILE(*newfile) a file to point to.  
The way this works is that it is what is called a stream.  That means that it is where the
output will go to.  To direct *newfile to a file the command to use is FILE *fopen(const char
*filename, const char *mode), found in stdio.h.  It simply returns a pointer to a FILE, but it is easy enough to use.  For example:

FILE *newfile: //Creates a FILE called newfile
newfile=fopen("c:\AUTOEXEC.BAT", "r");//open up for reading your autoexec.bat file, and assign   
                                                                          //it to newfile

        Basically, fopen accepts two strings.  One of them is the file name, including the path,and
the other is what the file will be used for(the mode).  In this case, the r designates the file will only be opened for reading.  Therefore, the file cannot be modified while it is open.  That is probably a good idea, because editing your autoexec.bat file with giberish is not a good idea!
        
        For a reference here is a chart listing the different ways you open a file:

r       Open for reading only.

w       Creates a file for writing. If a file by that name already exists, it will be overwritten.

a       Append; open for writing at the end of the file, or create the file if it does not exist.

r+      Open an existing file for reading and writing.

w+      Create a new file for reading and writing. If a file by that name already exists, it will 
    be overwritten.

a+      Open for append; open (or create if the file does not exist) for update at the end of the
    file.
        
        Keep in mind that each of these has a different use, and that you should choose the one 
most appropriate for you task.  For now however, lets concentrate on reading a file.

        Now, let's say you want to print the contents of autoexec.bat to your screen.  Assuming you 
want to make a program to do this you would need a function for reading from a file.  There are numerous useful ones, but for now we will use int fgetc(FILE *stream)(Note that it returns an int, but the range will still be printable(so it is the same as a char), defined in iostream.h.  Basically, fgetc will get the next character from a file you give it(that is, the stream you give it).  An example would be the following code to display the first few characters of your autoexec.bat file:


#include <iostream.h> //For cout
#include <stdio.h>  //For all file i/o functions

void main()
{
  int count=0; //Just a variable to keep from reading the file forever.
  FILE *afile;  //We need a FILE to point to the stream to allow access to the fil
  afile=fopen("c:\AUTOEXEC.BAT", "r"); //Open up the autoexec.bat file for reading
  while(count<10)
  {
    cout<<fgetc(afile); //Notice that fgetc returns an int, which can be printed.
    count++;            //I don't think it should read forever, right?
  }
  fclose(afile);                //A surprise(don't worry, just use it to close a file when done).
                                                //Just put in the pointer to the stream(the FILE thingy)
 }

        This program is fairly simple, and it does not take advantage of many of C's more useful 
file operations.  Note though, that it is going to print out only a few characters.  What if you wanted to print the entire file out, though?  Well, that is where a thing called the EOF(end-of-file) comes into play.  It is essentially a null that will signal the end of the file has been reached.  
        So, how would you make a program to use this?  Well, fgetc retrieves a character from the 
file, and it will return the EOF when it reaches the end of the file.  Now, it is possible to use a loop that will check to see if the last character is equal to the EOF.  For example, CHARACTERREAD!=EOF.  This would return true if the CHARACTERREAD is not the EOF.
        Here's how I would do it:
        
#include <iostream.h> //For cout
#include <stdio.h>   //For all file i/o functions

void main()
{
 FILE *afile;   //We need to define a FILE type to open a file
 afile=fopen("c:\AUTOEXEC.BAT", "r");  //Opens autoexec.bat, only to read, not write it.  afile
                                                                           //is now  the stream pointing to the file autoexec.bat, 
                                                                           //and is used to do operations with autoexec.bat
 char c;     //Without a character to store the information the program won't work
 while(c!=EOF) //Checking to see if the character just read is the end of the file
 {
   c=fgetc(afile); //This reads in the character
     cout<<c; //The prints out the character(as you SHOULD know!)
 }
 fclose(afile); //Just to be safe, close the file!
}

        Ok, so you finally got it to print out!  Well, what is the next thing to do?  Why not have
a program to make a backup of autoexec.bat?  There is a new function that you will need to add to your repetoire before this can be done.  The new function is fputc, defined in stdio.h.  int futc(int c, FILE *filethinghere);.  Basically, it will return the character given to it, or it will return an EOF.  It accepts a character as the first argument, and a pointer to a stream(the FILE thing) as the second argument.  Here is an example of how to use it:

fputc('A', newfile); //Writes the character 'A' to the file pointed to by newfile

        However, don't forget that this does not always work.  The file the stream points to has to 
have been opened for writing, not just reading.  Usually you will want to append to a file, but in the case of our next example we want to create a new file, and overwrite an old one.
        Now that we have a function to print to a file, why not finish up with one program to 
backup autoexec.bat.  Basically, we will use the same loop as in the first function, that is, checking to see if the end of the file is reached, otherwise it will continue to print out characters.  This time however, it will not print the characters to the screen.  Instead, it will print the characters to another file(In the example, backup.aut).

-----------------------------------------------------------------------------------------------
WARNING: If you currently have a file called backup.aut you will have it overwritten!  DO NOT run the example program if you have the file backup.aut in the directory with your compiler!  Otherwise, you will hae it overwritten.
-----------------------------------------------------------------------------------------------

#include <stdio.h> //Needed for file i/o functions(including fopen!)

void main()
{
  FILE *autoexec, *backup; //There are two files this time, the AUTOEXEC.BAT and the backup                     
                                                        // file
  autoexec=fopen("c:\AUTOEXEC.BAT", "r");//Open autoexec.bat to read the file
  backup=fopen("backup.aut", "w"); //Create(or overwrite)backup.aut for writing
  char c;  //We need a buffer for reading in the charactesr
  while(c!=EOF)  //Just checking to see if it's the end of the file
  {
    c=fgetc(autoexec); //Reading in a character from autoexec.bat
        fputc(c, backup); //Writing a character to the backup file!
  }
  fclose(autoexec);
  fclose(backup);  //Closing the files to finish it all up!
} 
 
        Wow!  It's a program that could be useful.  Feel free to use it anytime you like.  Just 
remember how it works.  Don't think this is the end of the file i/o information.  There is more, but for now this should be enough to whet your appetite.  Oh, and you case use fputc to write user input to a file also!  I think you can figure it out!

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 :)