Section 8.8 Rectangles
Now let’s say that we want to create a structure to represent a rectangle. The question is, what information do I have to provide in order to specify a rectangle? To keep things simple let’s assume that the rectangle will be oriented vertically or horizontally, never at an angle.
There are a few possibilities: I could specify the center of the rectangle (two coordinates) and its size (width and height), or I could specify one of the corners and the size, or I could specify two opposing corners.
The most common choice in existing programs is to specify the upper left corner of the rectangle and the size. To do that in C++, we will define a structure that contains a
Point
and two doubles.
struct Rectangle {
Point corner;
double width, height;
};
Notice that one structure can contain another. In fact, this sort of thing is quite common. Of course, this means that in order to create a
Rectangle
, we have to create a Point
first:
Point corner = { 0.0, 0.0 };
Rectangle box = { corner, 100.0, 200.0 };
This code creates a new
Rectangle
structure and initializes the instance variables. The figure shows the effect of this assignment.

’box’ names a box that contains three variables: ’width’ which is 100, ’height’ which is 200, and ’corner’ which names a package that has ’x: 0’ and ’y: 0’."
box.width += 50.0;
cout << box.height << endl;
In order to access the instance variables of
corner
, we can use a temporary variable:
Point temp = box.corner;
double x = temp.x;
Alternatively, we can compose the two statements:
double x = box.corner.x;
It makes the most sense to read this statement from right to left: “Extract
x
from the corner
of the box
, and assign it to the local variable x
.”
While we are on the subject of composition, I should point out that you can, in fact, create the
Point
and the Rectangle
at the same time:
Rectangle box = { { 0.0, 0.0 }, 100.0, 200.0 };
The innermost squiggly braces are the coordinates of the corner point; together they make up the first of the three values that go into the new
Rectangle
. This statement is an example of nested structure.
Rectangle
structure. Feel free to modify the code and experiment around!Checkpoint 8.8.2.
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