Page 108 - Programming Microcontrollers in C

Structures 93

While it would not be difficult to execute these calculations without
the use of structures, it is obvious that the structure formulation of the
program makes a much simpler and easier to follow program. The vari­
ables and program elements are objects here rather than mere numbers.
C has a command called typedef. This command can rename
a specified type for the convenience of the programmer. It does not
create a new type, it merely renames an existing type. For example,
typedef int Miles;
typedef char Byte;
typedef int Word;
typedef long Dword;
are all valid typedef statements. After the above invocations, a
declaration

Miles m;
Byte a[20];
Word word;
Dword big;
would make m an int, a an array of 20 characters, word the type
int, and big a long. All that has happened is that these types are
a redefinition of the existing types. New types defined by typedefs
are usually written with an upper case first letter. This is a tradition,
not a requirement of the C language.
Structures used earlier could be modified by use of the typedef.
Consider

typedef struct
{
int x;
int y;
} Point;

This typedef redefines the earlier struct point as Point. The
judicious use of typedefs can make a program even easier to read
than the simple use of structs. The program that follows is the
same as that above where all of the structures are typedef new names.

/* Inscribe a circle in a rectangle */