Objects in C++

What we just saw was an object interface. It defines how the rest of the world sees the object.
The first strange thing we saw was the line
```
// triangle.h
```
This was just a C++ style single line comment. Any line that begins with two forward slashes is considered a comment up to the end of the line.
Next, the line
```
class triangle
```
said that we were starting the definition of the triangle object. You can think of the class keyword as being like the struct keyword, except that class's can do much much more.
For example, you have control over how much of the class definition the rest of the program can see. The line
```
   public:
```
said that the stuff that follows can be used by anything. In contrast, the line
```
  private:
```
said that the stuff that follows can be used only by internal object functions. To give an example, say that I declare a triangle variable with the line
```
  triangle t;
```
Then the following lines are fine
```
  t.setTriangle( 3, 4, 5 );
  if ( t.valid() )
    printf( "%d", t.area() );
```
But
```
  t.s1 = 5.0;
```
isn't because s1 is a private data member of t and in C++, no one else can see your private parts.
The biggest way that classes differ from structs is that classes can contain functions. These are called member functions and are used (called) with the following syntax:
```
object-name . member-function-name ( function-arguments );
```
A member function with the same name as the object is called a constructor. Constructors are special in that (a) every object must have at least one, and (b) they are the function that is called when the object is created. For example, let's say that we added a constructor for our triangle class that looked like
```
	triangle(double side1, double side2, double s3);
```
Then we could either declare triangle objects like we did before with
```
	triangle t1, t2;
```
or using the new construct:
```
	triangle rightT(3.0, 4.0, 5.0 );
```
Next Slide