Working with COBOL Tables

In this article, we will delve deeper into the advanced concepts surrounding COBOL tables, also known as arrays, and discover how they can be effectively utilized in your COBOL programs. Although tables can initially appear complex, they are powerful data structures that significantly enhance the capabilities of your COBOL applications.

Understanding COBOL Tables

In COBOL, a table is essentially a collection of elements referenced by a single name and accessed via an index. This means you can store multiple items of the same data type in a structured manner, making handling large datasets easier. Tables in COBOL can dynamically hold records such as employee details, sales data, or any other structured information that requires the organization.

Definition of a Table

To define a table in COBOL, you use the OCCURS clause within the DATA DIVISION. Here’s a simple example:

01  EMPLOYEE-RECORD.
    05 EMPLOYEE-ID       PIC 9(5).
    05 EMPLOYEE-NAME     PIC A(50).
    05 EMPLOYEE-SALARY   PIC 9(6)V99.

01  EMPLOYEES-TABLE.
    05 EMPLOYEES OCCURS 100 TIMES.
       10 EMPLOYEE-DATA REDEFINES EMPLOYEE-RECORD.

In this example, the EMPLOYEES table can hold 100 records of employee data, where each record consists of an ID, name, and salary.

Accessing Table Elements

To access and manipulate the elements of a COBOL table, you can use indexes or subscripts. Both methods are effective but offer different flexibility levels. Subscripts start at 1, and you can specify the exact value:

MOVE 'John Doe' TO EMPLOYEES(1).EMPLOYEE-NAME.

In the example above, we assigned the name ‘John Doe’ to the first employee in our table. Similarly, if you wish to use an index, it is defined as follows:

01  EMPLOYEE-INDEX      PIC 9(3) VALUE 1.

MOVE 'Jane Doe' TO EMPLOYEES(EMPLOYEE-INDEX).EMPLOYEE-NAME.

Array Bounds and Dynamic Tables

While defining a table with a static size can suit certain scenarios, COBOL also allows for dynamic tables. Dynamic tables can expand based on your program needs. Although COBOL traditionally doesn't support dynamic memory allocation like modern languages, you can implement a workaround using the ALLOCATE statement in certain compiler environments.

For instance, if your program needs flexibility in the number of employees it processes, consider the use of pointers or a similar structure, depending on your compiler.

Advanced Table Operations

Searching Within Tables

Finding an element in a COBOL table can be accomplished with a PERFORM loop that checks each entry. For instance, if you want to find an employee by ID, you can use the following logic:

01  SEARCH-EMP-ID        PIC 9(5).
01  FOUND-EMP            PIC X(50) VALUE SPACES.
01  INDEX                PIC 9(3).
    
MOVE '10001' TO SEARCH-EMP-ID.
PERFORM VARYING INDEX FROM 1 BY 1 UNTIL INDEX > 100
   IF EMPLOYEES(INDEX).EMPLOYEE-ID = SEARCH-EMP-ID
      MOVE EMPLOYEES(INDEX).EMPLOYEE-NAME TO FOUND-EMP
   END-IF
END-PERFORM.

IF FOUND-EMP NOT = SPACES
   DISPLAY "Found Employee: " FOUND-EMP
ELSE
   DISPLAY "Employee not found."
END-IF.

In the above code, we iterate through the EMPLOYEES table until we locate the one matching the SEARCH-EMP-ID. The result gets displayed, letting us know if the employee was found.

Sorting COBOL Tables

Sorting tables is another vital skill. COBOL provides the SORT statement, which can be quite effective. Here’s how you can sort an employee table based on the salary:

SORT EMPLOYEES-TABLE ON ASCENDING KEY EMPLOYEE-SALARY
   USING EMPLOYEES
   GIVING SORTED-EMPLOYEES.

After sorting, you can work with the SORTED-EMPLOYEES table, which now contains the employees ordered by their salary. Always remember that sorting can be resource-intensive, so use it only when necessary!

Nested Tables

One remarkable feature in COBOL is the ability to create nested tables. This allows a table within a table which can represent more complex data relationships, such as an employee and their respective projects. Here's how you define nested tables:

01  PROJECT-RECORD.
    05 PROJECT-ID       PIC 9(5).
    05 PROJECT-NAME     PIC A(50).

01  EMPLOYEE-PROJECTS.
    05 PROJECTS OCCURS 10 TIMES.
       10 PROJECT-DATA REDEFINES PROJECT-RECORD.
01  EMPLOYEES-TABLE.
    05 EMPLOYEES OCCURS 100 TIMES.
       10 EMPLOYEE-DATA REDEFINES EMPLOYEE-RECORD.
       10 EMPLOYEE-PROJECTS.

When working with nested table structures, the principle of subscripting and indexing applies to each level.

Conclusion

Working with COBOL tables opens up various possibilities for efficiency and organization within your applications. By understanding how to define, access, sort, and manipulate tables, you can effectively manage collections of data and enhance your COBOL applications' functionality. Whether building simple employee records or establishing complex nested data structures, mastering these concepts will serve you well in your COBOL programming journey.

As we move forward in our COBOL series, remember that tables represent just one facet of this multifaceted programming language. Further articles will cover even more advanced topics, so keep an eye out for what’s next. Happy coding!

Programming - COBOL