Sams Teach Yourself C in 21 Days

Implementing Structures, Unions, and TypeDefs 255

11

You could have combined the definition and declaration, as you did before for the type

coord:

struct rectangle {

struct coord topleft;

struct coord bottomrt;

} mybox;

To access the actual data locations (the type intmembers), you must apply the member

operator (.) twice. Thus, the expression

mybox.topleft.x

refers to the xmember of the topleftmember of the type rectanglestructure named

mybox. To define a rectangle with coordinates ( 0 , 10 ),( 100 , 200 ), you would write

mybox.topleft.x = 0;

mybox.topleft.y = 10;

mybox.bottomrt.x = 100;

mybox.bottomrt.y = 200;

Maybe this is a bit confusing. You will understand better if you look at Figure 11.1,

which shows the relationship between the type rectanglestructure, the two type coord

structures it contains, and the two type intvariables each type coordstructure contains.

These structures are named as in the preceding example.

FIGURE11.1

The relationship

between a structure,

structures within a

structure, and the

structure members.

mybox.topleft.x

mybox.topleft.y

mybox.bottomrt.x

mybox.bottomrt.y

{

{

{

{

A type int variable (x)

A type int variable (y)

A type int variable (x)

A type int variable (y)

{

{

A type coord

structure (topleft)

A type coord

structure (bottomrt)

A type rectangle

structure (mybox)

{

Listing 11.2 presents an example of using structures that contain other structures. This

listing takes input from the user for the coordinates of a rectangle and then calculates and

displays the rectangle’s area. Note the program’s assumptions, given in comments near

the start of the program (lines 3 through 8).

LISTING11.2 struct.c. A demonstration of structures that contain other structures

1: /* Demonstrates structures that contain other structures. */

2:

3: /* Receives input for corner coordinates of a rectangle and

4: calculates the area. Assumes that the y coordinate of the

5: lower-right corner is greater than the y coordinate of the

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