Campbell CR6 Series, Руководство оператора

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Section 7. Installation
198
Constants, in memory, are four-byte signed integers or floating point numbers of
up to about 500 characters in length (length limited to the maximum
command
line
(p. 576)
length).
CRBasic syntax does not have a provision for declaring a data type for a constant,
so the compiler infers data type based on the format of the constant value
expression, which is usually a single scalar. There are three possible outcomes:
• string — the constant expression produces a string or the value is
enclosed in quotes
•
integer — the constant expression does not produce a floating point
v alue or the constant does not have a decimal point. Range =
–2,147,483,648 to 2,147,483,647
•
floating point. Range ≈ –1E38 to 1E38
If the constant is not written as a decimal, the compiler treats the value as an
integer. Integer and floating point values are represented by 32 bits. A
floating-point value achieves its extended range by using a base-two exponential
format. The range of integers that a floating-point value can reliably store is
limited by the size of the mantissa, which is ± 16,777,216. If the attempt is made
to express a floating-point constant outside of this range, precision may be lost.
Constants in a constant table can also be changed using the SetSetting()
instruction and the constant table using the CR1000KD.
Note Using all uppercase for constant names may make them easier to
recognize.
Using the Const Declaration
'This program example demonstrates the use of the Const declaration.
'Declare variables
Public PTempC
Public PTempF
'Declare constants
Const CtoF_Mult = 1.8
Const CtoF_Offset = 32
BeginProg
Scan (1,Sec,0,0)
PanelTemp (PTempC,250)
PTempF = PTempC * Cto CtoF_Offset
NextScan
EndProg
7.6.3.8.1 Predefined Constants
Many words are reserved for use by CRBasic. These words cannot be used as
variable or table names in a program. Predefined constants include instruction
names and valid alphanumeric names for instruction parameters. On account the