CICS Program Logic

Program logic in CICS refers to the structure, patterns, and conventions used when coding CICS applications. Understanding CICS-specific programming patterns is essential for creating robust, efficient, and maintainable mainframe applications.

Core CICS Programming Concepts

Transaction-Based Programming

CICS programs are invoked as transactions, which means they start from a known state and execute until completion:

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PROGRAM-ID. ORDER-PROCESSOR IS PROCESSING PROGRAM.
WORKING-STORAGE SECTION.
01 WS-CURRENT-DATE PIC X(10).
01 WS-TRANSACTION-ID PIC X(4) VALUE 'ORD1'.
 
PROCEDURE DIVISION.
0000-MAIN-LOGIC.
    PERFORM INITIALIZE-PROGRAM
    PERFORM READ-TERMINAL-INPUT
    PERFORM VALIDATE-INPUT-DATA
    PERFORM PROCESS-BUSINESS-LOGIC
    PERFORM WRITE-TERMINAL-OUTPUT
    PERFORM TERMINATE-PROGRAM
    
0000-EXIT.
    EXEC CICS RETURN END-EXEC.

State Management

CICS programs typically maintain state through working storage variables and external data storage:

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WORKING-STORAGE SECTION.
01 WS-PROGRAM-STATE.
    10 WS-INITIALIZATION-COMPLETE PIC X(1) VALUE 'N'.
    10 WS-DATA-VALIDATION-STATUS PIC X(1) VALUE 'N'.
    10 WS-PROCESSING-STATUS PIC X(1) VALUE 'N'.
    10 WS-OUTPUT-GENERATED PIC X(1) VALUE 'N'.
 
01 WS-CURRENT-TIME.
    10 WS-HOURS PIC 99.
    10 WS-MINUTES PIC 99.
    10 WS-SECONDS PIC 99.

Initialize program state at startup:

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INITIALIZE-PROGRAM.
    MOVE 'N' TO WS-INITIALIZATION-COMPLETE
    MOVE 'N' TO WS-DATA-VALIDATION-STATUS
    MOVE 'N' TO WS-PROCESSING-STATUS
    MOVE 'N' TO WS-OUTPUT-GENERATED
    
    EXEC CICS ASKTIME
        ABSTIME(WS-ABSOLUTE-TIME)
        RESP(WS-RESPONSE)
    END-EXEC.
    
    EXEC CICS FORMATTIME
        ABSTIME(WS-ABSOLUTE-TIME)
        TIME(WS-CURRENT-TIME)
        RESP(WS-RESPONSE)
    END-EXEC.
    
    MOVE 'Y' TO WS-INITIALIZATION-COMPLETE.

Program Flow Patterns

Linear Processing Pattern

Simple sequential processing from input to output:

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SEQUENTIAL-PROCESSING.
    PERFORM READ-INPUT-DATA
    PERFORM PROCESS-BUSINESS-RULES
    PERFORM UPDATE-DATABASE
    PERFORM SEND-OUTPUT-DATA
    PERFORM CLEANUP-RESOURCES.

Menu-Driven Pattern

Interactive programs presenting multiple options:

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MENU-DRIVEN-PATTERN.
    PERFORM DISPLAY-MENU-OPTIONS
    
    PERFORM UNTIL WS-EXIT-SELECTED
        PERFORM READ-USER-SELECTION
        
        EVALUATE WS-USER-SELECTION
            WHEN '1'
                PERFORM OPTION-CREATE-ACCOUNT
            WHEN '2'
                PERFORM OPTION-INQUIRE-ACCOUNT
            WHEN '3'
                PERFORM OPTION-UPDATE-ACCOUNT
            WHEN 'D'
                PERFORM OPTION-DELETE-ACCOUNT
            WHEN 'X'
                SET WS-EXIT-SELECTED TO TRUE
            WHEN OTHER
                PERFORM DISPLAY-INVALID-SELECTION
        END-EVALUATE
    END-PERFORM.

Validation-Driven Pattern

Programs that validate input before processing:

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VALIDATION-DRIVEN-PATTERN.
    PERFORM READ-INPUT-DATA
    
    PERFORM UNTIL WS-VALIDATION-SUCCESSFUL
        PERFORM VALIDATE-DATA-FORMAT
        PERFORM VALIDATE-DATA-CONTENT
        PERFORM VALIDATE-BUSINESS-RULES
        
        IF WS-VALIDATION-SUCCESSFUL
            PERFORM PROCESS-VALIDATED-DATA
        ELSE
            PERFORM DISPLAY-VALIDATION-ERRORS
            PERFORM READ-INPUT-DATA-AGAIN
        END-IF
    END-PERFORM.

Error Handling Logic

Response Code Checking

Always check CICS response codes for successful completion:

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WORKING-STORAGE SECTION.
01 WS-RESPONSE-CODES.
    02 WS-RESPONSE PIC S9(8) COMP.
    02 WS-RESPONSE2 PIC S9(8) COMP.
 
PROCEDURE DIVISION.
STANDARD-CICS-CALL.
    EXEC CICS READ FILE('CUSTOMER')
        INTO(WS-CUSTOMER-RECORD)
        RIDFLD(WS-CUSTOMER-ID)
        RESP(WS-RESPONSE)
    END-EXEC.
    
    EVALUATE WS-RESPONSE
        WHEN DFHRESP(NORMAL)
            PERFORM PROCESS-CUSTOMER-RECORD
        WHEN DFHRESP(NOTFND)
            PERFORM HANDLE-CUSTOMER-NOT-FOUND
        WHEN DFHRESP(FILEERR)
        WHEN DFHRESP(IOERR)
            PERFORM HANDLE-FILE-ERROR
        WHEN OTHER
            PERFORM HANDLE-UNEXPECTED-ERROR
    END-EVALUATE.

Graceful Degradation

Implement fallback logic when primary operations fail:

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GRACEFUL-DEGRADATION.
    PERFORM ATTEMPT-PRIMARY-PROCESSING
P    
    
    IF WS-PRIMARY-SUCCESSFUL
        PERFORM PRIMARY-PROCESSING-COMPLETION
    ELSE
        DISPLAY 'WARNING: Primary processing failed'
        PERFORM ATTEMPT-SECONDARY-PROCESSING
        
        IF WS-SECONDARY-SUCCESSFUL
            DISPLAY 'Secondary processing successful'
        ELSE
            PERFORM HANDLE-COMPLETE-FAILURE
        END-IF
    END-IF.

Data Access Patterns

Database Access Pattern

Standard pattern for database operations:

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DATABASE-ACCESS-PATTERN.
    * Open transaction context
    PERFORM BEGIN-TRANSACTION
    
    PERFORM VARYING WS-RECORD-COUNT FROM 1 BY 1
        UNTIL WS-RECORD-COUNT > WS-TOTAL-RECORDS
        
        PERFORM READ-DATABASE-RECORD
        
        IF WS-RESPONSE = DFHRESP(NORMAL)
            PERFORM UPDATE-RECORD-FIELDS
            PERFORM WRITE-DATABASE-RECORD
        ELSE
            PERFORM HANDLE-DATABASE-ERROR
        END-IF
    END-PERFORM.
    
    * Commit transaction
    PERFORM COMMIT-TRANSACTION.
 
BEGIN-TRANSACTION.
    EXEC CICS START TRANSID('SQ02')
        RESP(WS-RESPONSE)
    END-EXEC.

File Access Pattern

Sequential file processing:

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SEQUENTIAL-FILE-PATTERN.
    EXEC CICS STARTBR FILE('ORDER-FILE')
        GTEQ KEY(WS-START-KEY)
        RESP(WS-RESPONSE)
    END-EXEC.
    
    IF WS-RESPONSE = DFHRESP(NORMAL)
        PERFORM UNTIL WS-END-OF-FILE
            EXEC CICS READNEXT FILE('ORDER-FILE')
                INTO(WS-ORDER-RECORD)
                RESP(WS-RESPONSE)
            END-EXEC
            
            EVALUATE WS-RESPONSE
                WHEN DFHRESP(NORMAL)
                    PERFORM PROCESS-ORDER-RECORD
                WHEN DFHRESP(END)
                    SET WS-END-OF-FILE TO TRUE
                WHEN OTHER
                    PERFORM HANDLE-FILE-ERROR
                    SET WS-END-OF-FILE TO TRUE
            END-EVALUATE
        END-PERFORM
        
        EXEC CICS ENDBR FILE('ORDER-FILE')
            RESP(WS-RESPONSE)
        END-EXEC
    END-IF.

Transaction Control Logic

The READ/MODIFY/WRITE Pattern

Standard pattern for update operations:

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READ-MODIFY-WRITE-PATTERN.
    PERFORM READ-DATABASE-RECORD
    
    IF WS-RESPONSE = DFHRESP(NORMAL)
        PERFORM UPDATE-RECORD-FIELDS
        
        * Check if modification is needed
        IF WS-DATA-CHANGED
            PERFORM WRITE-DATABASE-RECORD
            
            IF WS-RESPONSE NOT = DFHRESP(NORMAL)
                PERFORM HANDLE-WRITE-ERROR
            END-IF
        END-IF
    ELSE
        PERFORM HANDLE-READ-ERROR
    END-IF.

Abend Handling Pattern

Handle abend conditions gracefully:

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WORKING-STORAGE SECTION.
01 WS-ABEND-HANDLER.
    02 WS-ABEND-AVAILABLE PIC X(1).
    02 WS-ABEND-TIME PIC X(26).
 
HANDLE-ABEND-LOGIC.
    PERFORM RESET-RESPONSE-AREA
    
    * Start abend monitoring
    EXEC CICS HANDLE ABEND LABEL(ABEND-EXIT-ONLY)
        RESP(WS-RESPONSE)
    END-EXEC.
    
    * Perform potentially problematic operation
    PERFORM HIGH-RISK-OPERATION
    
    * Normal completion
    EXEC CICS RETURN END-EXEC.
    
ABEND-EXIT-ONLY.
    EXEC CICS ASSIGN ABEND-INFO(WS-ABEND-TIME)
        RESP(WS-RESPONSE)
    END-EXEC.

Modular Design Patterns

Screen Processing Module

Dedicated module for handling screen I/O:

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SCREEN-PROCESSING-MODULE.
    PERFORM MAP-NAME-RETRIEVEBUSINESS
    
    EVALUATE WS-RESPONSE
        WHEN DFHRESP(NORMAL)
            MOVE EIBAID TO WS-PF-KEY
            EVALUATE WS-PF-KEY
                WHEN DFHPF1
                    PERFORM PROCESS-FUNCTION-1
                WHEN DFHPF2
                    PERFORM PROCESS-FUNCTION-2
                WHEN DFHENTER
                    PERFORM PROCESS-ENTER-KEY
                WHEN OTHER
                    PERFORM DISPLAY-INVALID-KEY
            END-EVALUATE
            
        WHEN DFHRESP(MAPERROR)
            PERFORM HANDLE-MAP-ERROR
    END-EVALUATE.

Business Logic Module

Separate business logic from I/O operations:

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BUSINESS-LOGIC-MODULE.
    * Validate business rules
    PERFORM VALIDATE-CUSTOMER-CREDIT
    PERFORM VALIDATE-PRODUCT-AVAILABILITY
    PERFORM CALCULATE-ORDER-TOTAL
    PERFORM APPLY-DISCOUNTS
    PERFORM CALCULATE-TAX
    PERFORM COMPUTE-FINAL-COST
    PERFORM UPDATE-INVENTORY-LEVELS.

Performance Considerations

Efficient Data Structures

Design efficient data structures for performance:

Operation	Best Practice	Avoid
File Access	Use exact keys	Full table scans
Memory Usage	Reuse storage areas	Frequent GETMAIN/FREEMAIN
Resource Acquisition	Acquire once, use multiple	Multiple allocate/deallocate
Error Handling	Check after operations	Ignore response codes

Resource Optimization

Optimize resource usage in programs:

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RESOURCE-OPTIMIZATION.
    * Allocate resources at initialization
    EXEC CICS GETMAIN SET(WS-BUFFER-PTR) LENGTH(WS-BUFFER-LENGTH)
        INITIMG(SPACES)
        RESP(WS-RESPONSE)
    END-EXEC.
    
    IF WS-RESPONSE = DFHRESP(NORMAL)
        SET ADDRESS OF WS-BUFFER TO WS-BUFFER-PTR
        * Use buffer for multiple operations...
    END-IF.
    
    * Free resources at termination
FINALE-CLEANUP.
    IF WS-BUFFER-PTR NOT = NULL
        EXEC CICS FREEMAIN DATA(WS-BUFFER-PTR) RESP(WS-RESPONSE) END-EXEC
    END-IF.

Testing Strategies

Unit Testing Patterns

Structure programs for easy testing:

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TESTABLE-PROGRAM-STRUCTURE.
    * Main entry point
PROCEDURE DIVISION USING WS-TEST-PARMS.
    PERFORM INITIALIZE-PROGRAM
    PERFORM MAIN-LOGIC
    PERFORM TERMINATE-PROGRAM.
    
MAIN-LOGIC.
    IF WS-TEST-MODE = 'Y'
        PERFORM DUMMY-PROGRAM-ACTION
    ELSE
        PERFORM REAL-PROGRAM-ACTION
    END-IF.

Integration Testing

Design for integration testing:

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INTEGRATION-TESTING-LOGIC.
    * Check if running in test environment
    PERFORM GET-CURRENT-RESTART-TICKET
    PERFORM CHECK-RESTART-TICKET
    
    IF WS-RECOVERY-SUCCESSFUL = 'Y'
        PERFORM LOG-TEST-COMPLETION
        PERFORM MARK-TICKET-COMPLETE
    END-IF.
    
    PERFORM TICKET-TRACKING-FUNCTION.

Best Practices Summary

Program Organization

Always include proper initialization logic
Separate I/O logic from business logic
Use meaningful paragraph names
Implement comprehensive error handling
Clean up resources before termination

Error Handling

Check all CICS response codes
Log errors for debugging
Provide meaningful error messages
Implement graceful degradation
Never ignore unexpected conditions

Performance

Avoid unnecessary CICS commands
Use efficient data structures
Minimize resource allocation/deallocation
Optimize file access patterns
Monitor resource usage

CICS Program Logic

Core CICS Programming Concepts

Transaction-Based Programming

State Management

Program Flow Patterns

Linear Processing Pattern

Menu-Driven Pattern

Validation-Driven Pattern

Error Handling Logic

Response Code Checking

Graceful Degradation

Data Access Patterns

Database Access Pattern

File Access Pattern

Transaction Control Logic

The READ/MODIFY/WRITE Pattern

Abend Handling Pattern

Modular Design Patterns

Screen Processing Module

Business Logic Module

Performance Considerations

Efficient Data Structures

Resource Optimization

Testing Strategies

Unit Testing Patterns

Integration Testing

Best Practices Summary

Program Organization

Error Handling

Performance

CICS Error Handling

CICS Programs

PERFORM Command

RETURN Command