What is the CALL statement in COBOL?

The CALL statement in COBOL is used to invoke subprograms (subroutines) from the main program, enabling modular programming and code reuse through subprogram communication.

How do you pass parameters using CALL statement?

Parameters are passed using the USING clause in the CALL statement, which maps data items from the calling program to the linkage section of the called subprogram.

What is the linkage section in COBOL?

The linkage section defines parameters that are passed between programs, containing data items that are shared between the calling program and the called subprogram.

How do you handle return values from CALL statements?

Return values are handled through the linkage section parameters, return codes, or by modifying shared data items that are passed by reference.

What are the benefits of using CALL statements?

Benefits include code modularity, reusability, maintainability, separation of concerns, and the ability to create libraries of common functions.

How do you handle errors in CALL statements?

Errors are handled through return codes, exception handling, validation of parameters, and proper error checking after the CALL statement execution.

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COBOL Call Statement

The CALL statement in COBOL is a fundamental mechanism for invoking subprograms, enabling modular programming and code reuse. It allows programs to communicate with other programs, pass parameters, and receive return values, making COBOL applications more maintainable and organized.

Understanding the CALL Statement

The CALL statement transfers control from the calling program to a subprogram, executes the subprogram, and then returns control to the calling program. This mechanism enables code modularity, reusability, and separation of concerns in COBOL applications.

Basic CALL Statement Syntax

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       CALL 'subprogram-name' USING parameter-list
           ON EXCEPTION
               error-handling-statements
           NOT ON EXCEPTION
               success-handling-statements
       END-CALL.

Simple CALL Statement Example

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       IDENTIFICATION DIVISION.
       PROGRAM-ID. MAIN-PROGRAM.
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01 CALCULATION-DATA.
           05 FIRST-NUMBER    PIC 9(5)V99.
           05 SECOND-NUMBER   PIC 9(5)V99.
           05 RESULT          PIC 9(6)V99.
           05 OPERATION       PIC X(1).
               88 ADDITION VALUE 'A'.
               88 SUBTRACTION VALUE 'S'.
               88 MULTIPLICATION VALUE 'M'.
               88 DIVISION VALUE 'D'.
       
       01 RETURN-CODE.
           05 RC              PIC 9(2).
               88 SUCCESS VALUE 00.
               88 ERROR VALUE 99.
       
       PROCEDURE DIVISION.
       MAIN-LOGIC.
           MOVE 100.50 TO FIRST-NUMBER
           MOVE 25.25 TO SECOND-NUMBER
           MOVE 'A' TO OPERATION
           
           CALL 'CALCULATOR' USING CALCULATION-DATA RETURN-CODE
           
           IF SUCCESS
               DISPLAY 'Result: ' RESULT
           ELSE
               DISPLAY 'Calculation Error'
           END-IF
           
           STOP RUN.

Subprogram Structure

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       IDENTIFICATION DIVISION.
       PROGRAM-ID. CALCULATOR.
       DATA DIVISION.
       LINKAGE SECTION.
       01 CALCULATION-DATA.
           05 FIRST-NUMBER    PIC 9(5)V99.
           05 SECOND-NUMBER   PIC 9(5)V99.
           05 RESULT          PIC 9(6)V99.
           05 OPERATION       PIC X(1).
       
       01 RETURN-CODE.
           05 RC              PIC 9(2).
       
       PROCEDURE DIVISION USING CALCULATION-DATA RETURN-CODE.
       MAIN-CALCULATION.
           EVALUATE OPERATION
               WHEN 'A'
                   ADD FIRST-NUMBER TO SECOND-NUMBER GIVING RESULT
                   MOVE 00 TO RC
               WHEN 'S'
                   SUBTRACT SECOND-NUMBER FROM FIRST-NUMBER GIVING RESULT
                   MOVE 00 TO RC
               WHEN 'M'
                   MULTIPLY FIRST-NUMBER BY SECOND-NUMBER GIVING RESULT
                   MOVE 00 TO RC
               WHEN 'D'
                   IF SECOND-NUMBER NOT = ZERO
                       DIVIDE FIRST-NUMBER BY SECOND-NUMBER GIVING RESULT
                       MOVE 00 TO RC
                   ELSE
                       MOVE 99 TO RC
                   END-IF
               WHEN OTHER
                   MOVE 99 TO RC
           END-EVALUATE
           
           EXIT PROGRAM.

Parameter Passing Methods

1. By Reference (Default)

Parameters are passed by reference, meaning the subprogram works with the actual data items from the calling program.

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       CALL 'PROCESS-DATA' USING CUSTOMER-RECORD
                                 TRANSACTION-AMOUNT
                                 RESULT-STATUS.

2. By Content

Parameters are passed by content, creating a copy of the data for the subprogram to use.

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       CALL 'VALIDATE-DATE' USING BY CONTENT INPUT-DATE
                                   BY REFERENCE VALIDATION-RESULT.

3. Mixed Parameter Passing

Combine both reference and content parameter passing in a single CALL statement.

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       CALL 'PROCESS-ORDER' USING BY REFERENCE ORDER-DATA
                                   BY CONTENT PROCESSING-DATE
                                   BY REFERENCE ORDER-STATUS.

Error Handling in CALL Statements

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       PROCEDURE DIVISION.
       CALL-WITH-ERROR-HANDLING.
           CALL 'FILE-PROCESSOR' USING FILE-DATA
               ON EXCEPTION
                   DISPLAY 'Error: Subprogram not found'
                   MOVE 99 TO RETURN-CODE
               NOT ON EXCEPTION
                   IF RETURN-CODE = 00
                       DISPLAY 'File processing successful'
                   ELSE
                       DISPLAY 'File processing failed'
                   END-IF
           END-CALL.

Dynamic CALL Statements

Dynamic CALL statements allow program names to be determined at runtime, providing flexibility in program execution.

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       WORKING-STORAGE SECTION.
       01 DYNAMIC-PROGRAM-NAME PIC X(20).
       01 PROGRAM-SELECTION   PIC X(1).
           88 REPORT-PROGRAM VALUE 'R'.
           88 UPDATE-PROGRAM VALUE 'U'.
           88 QUERY-PROGRAM VALUE 'Q'.
       
       PROCEDURE DIVISION.
       DYNAMIC-CALL-PROCESSING.
           PERFORM SELECT-PROGRAM-NAME
           CALL DYNAMIC-PROGRAM-NAME USING PARAMETER-LIST
               ON EXCEPTION
                   DISPLAY 'Program not available: ' DYNAMIC-PROGRAM-NAME
           END-CALL.
       
       SELECT-PROGRAM-NAME.
           EVALUATE PROGRAM-SELECTION
               WHEN 'R'
                   MOVE 'GENERATE-REPORT' TO DYNAMIC-PROGRAM-NAME
               WHEN 'U'
                   MOVE 'UPDATE-RECORDS' TO DYNAMIC-PROGRAM-NAME
               WHEN 'Q'
                   MOVE 'QUERY-DATABASE' TO DYNAMIC-PROGRAM-NAME
               WHEN OTHER
                   MOVE 'DEFAULT-PROCESSOR' TO DYNAMIC-PROGRAM-NAME
           END-EVALUATE.

Nested CALL Statements

CALL statements can be nested, allowing subprograms to call other subprograms, creating a hierarchy of program calls.

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       PROCEDURE DIVISION.
       NESTED-CALL-EXAMPLE.
           CALL 'VALIDATE-INPUT' USING INPUT-DATA VALIDATION-RESULT
           
           IF VALIDATION-SUCCESSFUL
               CALL 'PROCESS-DATA' USING INPUT-DATA PROCESSING-RESULT
               
               IF PROCESSING-SUCCESSFUL
                   CALL 'GENERATE-OUTPUT' USING PROCESSING-RESULT OUTPUT-DATA
               END-IF
           END-IF.

Best Practices for CALL Statements

Parameter Validation: Validate parameters before calling subprograms
Error Handling: Always implement proper error handling
Return Codes: Use consistent return code conventions
Documentation: Document parameter requirements and return values
Testing: Test all parameter combinations and error conditions
Performance: Consider performance implications of frequent calls

Common CALL Statement Patterns

Utility Functions: Common calculations and data processing
Validation Routines: Data validation and error checking
File Operations: File processing and I/O operations
Report Generation: Report formatting and output
Database Operations: Database access and manipulation
Business Logic: Complex business rule implementation

COBOL Call Statement

Understanding the CALL Statement

Basic CALL Statement Syntax

Simple CALL Statement Example

Subprogram Structure

Parameter Passing Methods

1. By Reference (Default)

2. By Content

3. Mixed Parameter Passing

Error Handling in CALL Statements

Dynamic CALL Statements

Nested CALL Statements

Best Practices for CALL Statements

Common CALL Statement Patterns

Subprograms

Linkage Section

Parameter Passing

Modular Programming

Program Communication

Return Codes