Rockwell-automation 2098-IPD-xxx Ultra5000 C Programming using the Mot Manual de usuario descargar pdf (Pagina 30)

Publication 2098-PM001E-EN-P — July 2002

1-18 Programming Motion Control in C

Types, Operators, and

Expressions

The C language allows you a great deal of flexibility in deciding what

type of data the Ultra5000 will use. Some of the data is preset or static,

such as (#define ACCEL 1000), while other data changes or is assigned

different values as your program runs (long partcount; is an example).

The preset and unchanging data is called a constant, while the

changing data is called a variable. Expressions combine variables and

constants to produce new values.

Variable Names and Data Types/Sizes

You are already familiar with declaring one variable. The code

long target

declares the variable target as a long integer. This one line of code

covers the rules for C variables:

• Each variable must have a unique name.

• Variables must begin with a letter.

• Before you can use a variable, you must declare or define it by its

type. The following table lists the eight keywords for defining a

variable.

Keyword: Description: Example:

int Integer: A positive or negative value of up to

32-bits in length.

int main ()

long Long word: An integer of the maximum length,

32- bits with a range of ±2,147,483,647.

long int ()

short Short word: An integer smaller than the largest

integer; 32- bits in length.

short int ()

unsigned A non-negative number (i.e., a number greater

than or equal to 0).

unsigned int ()

or

unsigned int ()

char Typographic symbols, such as A, & and + or small

integers, up to 32-bits in length.

float A fractional value or a value with a decimal

point. 32-bits in length, but typically with a range

from 10

–38

to 10

38

.

salary ()

double A longer fractional or decimal value. It allows for

additional significant places and/or larger

exponents than a basic float. 32-bits in length,

but typically with a 10-digit base and an

exponent from –307 to 308.

Note: A long double typically provides an 18-digit

base and an exponent from –4931 to 4932.

double salary ()

signed A number with a positive or a negative value.

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