Page 25 - Programming Microcontrollers in C

10 Chapter 1 Introduction to C

long—modifies an int, and is a variable size whose width is
no less than that of an int. For example, on a 16-bit machine, an
int might be 16 bits, and a long int could be 32 bits. long can
also modify a double to specify an extended precision floating-point
number. You will find examples where a long and an int are the
same size.
signed—modifies all integral numbers and produces a range
of numbers that contains both positive and negative numbers. For
example, if the type char is 8 bits, a signed char can contain the
range of numbers –128 to +127. Default for char and int is
signed when they are declared.

unsigned—modifies all integral numbers and produces a range
of numbers that are positive only. For example, if the type char is 8
bits, an unsigned char can contain the range of numbers 0 to
+255. It is not necessary to include the type int with the qualifiers
short or long. Thus, the following statements are the same:
long int a,c;
short int d;
and

long a,c;
short d;
When a variable is defined, space is allocated in memory for its
storage. The basic variable size is implementation dependent, and
especially for microcontrollers, you will find that this variability will
show up when you change from one microcomputer to another.
Each variable must be defined prior to being used. A variable
may be defined at the beginning of any code block, and the variable’s
scope is the block in which it is defined. When the block in which the
variable is defined is exited, the variable goes out of existence. There
is no problem with defining variables with the same name in differ­
ent blocks. The compiler will make certain that these variables do
not get mixed up in the execution of the code.
An additional qualifier is const. When const is used as a quali­
fier on the declaration of any variable, an initialization value must be
declared. This value cannot be changed by the program. Therefore
the declaration