Page 24 - Programming Microcontrollers in C

Names 9

with an underscore. Because of this convention, you should avoid
the use of an underscore as the first character for either function or
variable names in your code. This approach will completely avoid
name conflict with these hidden or unexpected names. Compilers
usually allow the names to be unique in the first 31 characters. Un­
fortunately, some linkers used to link various program modules require
that the names be unique in the first six or eight characters, depend­
ing on the linker.
C has a collection of keywords that cannot be used for names.
These keywords are listed below:

KEYWORDS

auto double int struct
break else long switch

case enum register typedef
char extern return union
const float short unsigned
continue for signed void
default goto sizeof volatile
do if static while

Types and Type Declarations
C has only a few built-in types. Here they are:

char—is usually eight bits. The character is the smallest stor­
age unit.

int—an integer is usually the size of the basic unit of storage
for the machine. An int must be at least 16 bits wide.

float—a single precision floating-point number.
double—a double precision floating-point number.
Additional qualifiers are used to modify the basic types. These
qualifiers include:
short—modifies an int, and is a variable whose width is no
greater than that of the int. For example, with a compiler with a 32
bit int a short int could be 16 bits. You will find examples
where short and int are the same size.