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 <string.h> //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.

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