Lesson 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Before discussing classes, this lesson will be an introduction to data structures similar to classes. Structures are a way of storing many different variables of different types under the same name. This makes it a more modular program, which is easier to modify because its design makes things more compact. It is also useful for databases.
The format for declaring a structure(in C++, it is different in C) is
Where NAME is the name of the entire type of structure. To actually create a single structure the syntax is NAME name_of_single_structure; To access a variable of the structure it goes name_of_single_structure.name_of_variable;
example an_example; //Treating it like a normal variable type
an_example.x=33; //How to access it
Here is an example program:
database employee; //There is now an employee variable that has modifiable
//variables inside it.
The struct database declares that database has three variables in it, age, id_number, and salary.
You can use database like a variable type like int. You can create an employee with the database type as 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();
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. Its like a giant storage chest where you can store one large item, or a bunch of small items, but never the both at the same time.
The '.' operator is used to access different variables inside a union also.
As a final note, if you wish to have a pointer to a structure, to actually access the information stored inside the structure that is pointed to, you use the -> operator in place of the . operator.
A quick example:
ptr=&structure; //Yes, you need the & when dealing with structures
//and using pointers to them
cout<<ptr->x; //The -> acts somewhat like the * when used with pointers
//It says, get whatever is at that memory address
//Not "get what that memory address is"
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