Constant

Constant

What is the Constant?

A constant is a variable assigned with a value that does not change throughout the program execution. COBOL does not have any system-defined standards for constants except figurative constants.

The programmer can define a variable with an initial value using the VALUE clause during the variable declaration. If the variable value doesn't change during the program's execution, the variable is considered as a constant variable, and the value is considered as 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 example, it is 01.
  • constant-variable - Specifies the name of the constant. From example, it is WS-PI.
  • data-type-character - Specifies the type of the variable. From example, it is 9.
  • constant-length - Specifies the variable length to store the data. From example, it is 04.
  • constant-value - Specifies the constant value. From example, it is 3.14.

Types -

Constants are three types and those are –

  • Numeric constants – Numeric variables having one value throughout the program execution are called numeric constants. For example - 01 WS-PI PIC 9(2)V9(2) VALUE 3.14.
  • Alphanumeric constants/non-numeric constants – Alphanumeric variables that have only one value throughout the program execution are called as alphanumeric constants. They require literals enclosed with quotes while initializing them. For example - 01 WS-HI PIC X(05) VALUE "HI".
  • Figurative Constants - System-defined constants are predefined in the COBOL language and 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 -

----+----1----+----2----+----3----+----4----+----5----+
       IDENTIFICATION DIVISION.
       PROGRAM-ID. CONSTANT.
       AUTHOR. MTH.
       DATA DIVISION. 
       WORKING-STORAGE SECTION. 
       01  WS-VAR.
           05 WS-NUMCONST      PIC 9(10) VALUE 256.
           05 WS-NNUMCONST     PIC X(05) VALUE "TRUE".
           05 WS-FIGCONST      PIC X(10) VALUE ZEROES.
           05 WS-VAR1          PIC 9(10).
           05 WS-VAR2          PIC X(20).
       PROCEDURE DIVISION.
           MOVE 256            TO WS-VAR1.
           IF WS-VAR1 EQUAL WS-NUMCONST
              DISPLAY "WS-VAR1 VALUE EQUAL TO NUMERIC CONSTANT"
           ELSE 
              DISPLAY "WS-VAR1 VALUE NOT EQUAL TO NUMERIC CONSTANT"
           END-IF.

           MOVE "FALSE"       TO WS-VAR2.
           IF WS-VAR2 EQUAL WS-NNUMCONST 
              DISPLAY "WS-VAR2 VALUE EQUAL TO NON-NUMERIC CONSTANT"
           ELSE 
              DISPLAY "WS-VAR2 VALUE NOT EQUAL TO NON-NUMERIC CONSTANT" 
           END-IF.

           IF WS-FIGCONST EQUAL ZEROES
              DISPLAY "WS-FIGCONST IS FILLED WITH ZEROES"
              DISPLAY "FIGCONSTANT : " WS-FIGCONST 
           END-IF.
 
           STOP RUN.

Output -

WS-VAR1 VALUE EQUAL TO NUMERIC CONSTANT
WS-VAR2 VALUE NOT EQUAL TO NON-NUMERIC CONSTANT
WS-FIGCONST IS FILLED WITH ZEROES
FIGCONSTANT : 0000000000

Explaining Example -

In the above example:

  • We have declared three constant variables. i.e., WS-NUMCONST is a numeric constant with a constant value of 256.
  • WS-NNUMCONST is a non-numeric constant with a constant value of "TRUE".
  • Finally, WS-FIGCONST is a variable initialized with the figurative constant ZEROES.