Page 247 - Introduction to Microcontrollers Architecture, Programming, and Interfacing of The Motorola 68HC12

224 Chapter 8 Programming in C and C++

data. More than one variable can be put in a declaration; the variables are separated by
commas (,). A vector having n elements is denoted by the name and square brackets
around the number of elements «, and the elements are numbered 0 to n.— 1, For
example, the declaration int a, b[ 10 ]; shows two variables, a scalar variable a and a
vector b with ten elements. Variables declared outside the procedure (e.g., before the line
with procedure_name) are global, and those declared within a procedure (e.g., between
the curly brackets { and } after procedure_name) are local. Parameters will be discussed
in §8.5. A cast redefines a value's type. A cast is put in parentheses before the value. If
i is an int, (char) i is a char.
declaration of global variable;
declaration of global variable;
procedure_name (parameter_l, Parameter^,...)
{
declaration of local variable;
declaration of local variable;
statement;
statement;

}
Table 8.1. Conventional C Ooerators Used in Exoressions

Statements may be algebraic expressions that generate assembly-language
instructions to execute the procedure's activities. A statement may be replaced by a
sequence of statements within a pair of curly brackets ({ and }). This will be useful in
conditional and loop statements discussed soon. Operators used in statements include
addition, subtraction, multiplication, and division, and a number of very useful operators
that convert efficiently to assembly-language instructions or program segments. Table
8.1 shows the conventional C operators that we will use in this book. Although they are
not all necessary, we use a lot of parentheses so we will not have to learn the precedence
rules of C grammar. The following simple C procedure fun has (signed) 16-bit input
parameter a and 32-bit local variable b; it puts 1 into b and then puts the (a+b) th
element of the ten-element unsigned global 8-bit vector d into 8-bit unsigned global c
and returns nothing (void) as is indicated by the data type to the left of the procedure
name: