Constant Declaration

Main Index

Language Idx

Description
Syntax
Operation

Remarks
Example
Version History & Bug list

Description:

A Constant Declaration is a compiler directive that declares that an identifier has a specific value.

Syntax:

The following shows the format of the Constant Declaration syntax.

Basic	Const <constname> = <constvalue>
C	const <constname> = <constvalue>;
Java	final <constname> = <constvalue>;

The following table lists the elements of the Constant Declaration syntax.

Element	Description
<constname>	Name of the constant. Follows standard naming conventions.
<constvalue>	Value to be assigned to each place in program code that the <constname> is encountered.

Operation:

During compilation, when a Constant Declaration is encountered in the program's source code, the identifier specified by the <constname> and the value specified by the <constvalue> element are added to a list of constant values. Then, each subsequent time that the constant's identifier is encountered in the program's source code, the specified value is substituted in the compilation. The resulting compiled code would be the same as if the text of each occurrence of the identifier in the program's source code was replaced with the text of the value.

Remarks:

Constants can make your programs self-documenting and easy to modify. Unlike variables, constants can't be inadvertently changed while your program is running and they do not take up any RAM storage space.

Example:

In the following example programs, a Constant Declaration is shown that declares "DelayValue" to be equal to 100. This constant is then used to control the rate that an I/O Line changes state. If the rate needs to change, all the programmer needs to do is to change the value in the Constant Declaration, and both places that it is used will now use the new value.

Visual Basic Syntax

C Syntax

Dim A As New oDio1
Const DelayValue = 100

Sub Main()
  A.IOLine = 31
  A.Direction = cvOutput
  Do
    A.Set
    ooPIC.Delay = DelayValue
    A.Clear
    ooPIC.Delay = DelayValue
  Loop
End Sub

oDio1 A = New oDio1;
Const DelayValue = 100;

Sub void Main(void){
  A.IOLine = 31;
  A.Direction = cvOutput;
  Do{
    A.Set;
    ooPIC.Delay = DelayValue;
    A.Clear;
    ooPIC.Delay = DelayValue;
  } while (1);
}

Basic Syntax

Java Syntax

A As oDIO1(31,cvOutput)
DelayValue Con 100

Do
  A.Set
  ooPIC.Delay = DelayValue
  A.Clear
  ooPIC.Delay = DelayValue
Loop

oDio1 A = New oDio1;
Final DelayValue = 100;

Sub void Main(void){
  A.IOLine = 31;
  A.Direction = cvOutput;
  Do{
    A.Set;
    ooPIC.Delay = DelayValue;
    A.Clear;
    ooPIC.Delay = DelayValue;
  } while (1);
}

In the following examples, a constant value of 5 is defined with the name MaxNum.

Visul Basic	Const MaxNum = 5
Basic	MaxNum Con 5
C	Const MaxNum = 5;
Java	Final MaxNum = 5;

Version History and Bug List:

Firmware Ver A1: Introduced.

Bugs: No known bugs.