Constants

What is the Constant?

A constant is a value that does not change throughout the program execution.
COBOL does not have any system-defined standards for constants except figurative constants.
Using the VALUE clause, the programmer can declare a variable with an initial value. If the variable value doesn't change during the program's execution, the variable is considered a constant variable, and the value is considered a constant value.

Syntax -

 level-number constant-variable    
    PIC data-type-character(constant-length)
	VALUE constant-value.

For example - Declaring a variable to store a value 3.14 (PI value).

 01 WS-PI      PIC 9(2)V9(2) VALUE 3.14.

level-number - Specifies the level number of the declaration from 01 to 49. From above example, it is 01.
constant-variable - Specifies the name of the constant. From above example, it is WS-PI.
data-type-character - Specifies the type of the variable. From above example, it is 9.
constant-length - Specifies the variable length to store the data. From above example, it is 04.
constant-value - Specifies the constant value. From above example, it is 3.14.

Types -

Constants are three types, and those are –

Numeric constants – Numeric variables having only one value throughout the program execution are called numeric constants. For example - 01 WS-PI PIC 9(2)V9(2) VALUE 3.14.
Alphanumeric or non-numeric constants – Alphanumeric variables that have only one value throughout the program execution are called as alphanumeric constants. For example - 01 WS-HI PIC X(05) VALUE "HI".
Figurative Constants - System-defined constants predefined in COBOL are used as replacements for standard values like SPACES, ZEROES, etc. For example - 01 WS-VAR PIC 9(5) VALUE ZEROES.

For example -

01 A		PIC X(10) VALUE "MAINFRAMES".
01 B.
   02 C		PIC 9(3) VALUE 255.
   02 D  	PIC 9(3) VALUE ZEROES.

In the above example, A is a non-numeric constant variable, C is a numeric constant variable, and D is a figurative constant variable.

Practical Example -

Scenario - Example to describe how the constants are used in COBOL programming.

Code -

Full Example

----+----1----+----2----+----3----+----4----+----5----+
       ...
       WORKING-STORAGE SECTION.
       01 WS-VAR. 
          05 WS-PI        PIC 9V99 VALUE 3.14.
          05 WS-RADIUS    PIC 9(2).
          05 WS-AREA      PIC 9(3).9(2) VALUE ZEROES.
       ...
       PROCEDURE DIVISION.
           MOVE 5         TO WS-RADIUS.
           COMPUTE WS-AREA = WS-PI * WS-RADIUS * WS-RADIUS 
           DISPLAY "AREA OF CIRCLE:  " WS-AREA. 
		   ...

Output -

AREA OF CIRCLE:  078.50

Explaining Example -

In the above example:

3.14 value is not changed in the vriable WS-PI through out the program execution. So the WS-PI is called as constant variable and 3.14 is called as constant value.