COBOL Tutorial

COBOL BLANK Clause

The BLANK clause in COBOL is a powerful screen formatting and data manipulation feature used primarily in screen handling, report generation, and interactive applications to control field clearing, screen presentation, and data initialization. This clause provides essential functionality for creating professional user interfaces, managing screen real estate efficiently, controlling field visibility, and ensuring clean data presentation in both batch and interactive COBOL applications where screen formatting and field management are critical for user experience and data integrity.

Understanding BLANK Clause

The BLANK clause is used in screen section definitions and display operations to control how fields appear on the screen. It can clear existing field contents, provide visual separation, or initialize fields to a blank state for data entry operations.

Key Uses:

BLANK WHEN ZERO - Hide zero values in numeric displays
BLANK SCREEN - Clear entire screen for new displays
BLANK LINE - Clear specific screen lines
Field initialization and clearing operations
Professional screen formatting and presentation

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SCREEN SECTION.
01  MAIN-SCREEN.
    05  BLANK SCREEN.
    05  LINE 1 COL 20 VALUE "CUSTOMER INFORMATION SYSTEM".
    05  LINE 3 COL 10 VALUE "Customer ID:".
    05  LINE 3 COL 23 PIC 9(6) TO CUSTOMER-ID.
    05  LINE 4 COL 10 VALUE "Name:".
    05  LINE 4 COL 23 PIC X(30) TO CUSTOMER-NAME.
    05  LINE 5 COL 10 VALUE "Balance:".
    05  LINE 5 COL 23 PIC Z(8).99 BLANK WHEN ZERO TO BALANCE-AMT.
 
PROCEDURE DIVISION.
DISPLAY-CUSTOMER-SCREEN.
    DISPLAY MAIN-SCREEN.
    ACCEPT MAIN-SCREEN.

BLANK WHEN ZERO Implementation

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*> Professional numeric field formatting
DATA DIVISION.
WORKING-STORAGE SECTION.
01  FINANCIAL-REPORT.
    05  ACCOUNT-BALANCE    PIC S9(8)V99 COMP-3.
    05  INTEREST-EARNED    PIC S9(6)V99 COMP-3.
    05  FEES-CHARGED       PIC S9(5)V99 COMP-3.
    05  NET-AMOUNT         PIC S9(8)V99 COMP-3.
 
01  REPORT-DISPLAY-FIELDS.
    05  DISP-BALANCE       PIC Z(8).99 BLANK WHEN ZERO.
    05  DISP-INTEREST      PIC Z(6).99 BLANK WHEN ZERO.
    05  DISP-FEES          PIC Z(5).99 BLANK WHEN ZERO.
    05  DISP-NET           PIC Z(8).99 BLANK WHEN ZERO.
 
SCREEN SECTION.
01  FINANCIAL-SCREEN.
    05  BLANK SCREEN.
    05  LINE 2 COL 25 VALUE "FINANCIAL SUMMARY REPORT".
    05  LINE 4 COL 10 VALUE "Account Balance:".
    05  LINE 4 COL 30 FROM DISP-BALANCE.
    05  LINE 5 COL 10 VALUE "Interest Earned:".
    05  LINE 5 COL 30 FROM DISP-INTEREST.
    05  LINE 6 COL 10 VALUE "Fees Charged:".
    05  LINE 6 COL 30 FROM DISP-FEES.
    05  LINE 8 COL 10 VALUE "Net Amount:".
    05  LINE 8 COL 30 FROM DISP-NET HIGHLIGHT.
 
PROCEDURE DIVISION.
DISPLAY-FINANCIAL-REPORT.
    *> Move data to display fields
    MOVE ACCOUNT-BALANCE TO DISP-BALANCE.
    MOVE INTEREST-EARNED TO DISP-INTEREST.
    MOVE FEES-CHARGED TO DISP-FEES.
    MOVE NET-AMOUNT TO DISP-NET.
    
    *> Display formatted screen
    DISPLAY FINANCIAL-SCREEN.
    
    *> Example output - zero values don't display
    *> Account Balance:    1,234.56
    *> Interest Earned:              (blank if zero)
    *> Fees Charged:         25.00
    *> Net Amount:       1,209.56

Screen Management and Clearing

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*> Advanced screen management techniques
SCREEN SECTION.
01  MENU-SCREEN.
    05  BLANK SCREEN.
    05  LINE 1 COL 30 VALUE "MAIN MENU" HIGHLIGHT.
    05  LINE 3 COL 20 VALUE "1. Customer Management".
    05  LINE 4 COL 20 VALUE "2. Order Processing".
    05  LINE 5 COL 20 VALUE "3. Reports".
    05  LINE 6 COL 20 VALUE "4. System Administration".
    05  LINE 8 COL 20 VALUE "Enter choice (1-4):".
    05  LINE 8 COL 40 PIC 9 TO MENU-CHOICE.
 
01  ERROR-MESSAGE-SCREEN.
    05  LINE 20 COL 10 VALUE "ERROR: Invalid selection!".
    05  LINE 21 COL 10 VALUE "Press any key to continue...".
 
01  CONFIRMATION-SCREEN.
    05  LINE 15 COL 20 VALUE "Are you sure? (Y/N):".
    05  LINE 15 COL 42 PIC X TO CONFIRM-FLAG.
 
PROCEDURE DIVISION.
MAIN-MENU-LOOP.
    PERFORM UNTIL MENU-CHOICE = 4
        DISPLAY MENU-SCREEN
        ACCEPT MENU-CHOICE
        
        EVALUATE MENU-CHOICE
            WHEN 1
                PERFORM CUSTOMER-MANAGEMENT
            WHEN 2
                PERFORM ORDER-PROCESSING
            WHEN 3
                PERFORM REPORTS-MENU
            WHEN 4
                PERFORM EXIT-CONFIRMATION
            WHEN OTHER
                PERFORM DISPLAY-ERROR-MESSAGE
        END-EVALUATE
    END-PERFORM.
 
DISPLAY-ERROR-MESSAGE.
    DISPLAY ERROR-MESSAGE-SCREEN.
    ACCEPT DUMMY-FIELD.
    *> Screen automatically blanks on next DISPLAY.
 
CLEAR-SPECIFIC-LINES.
    *> Clear lines 15-20 for new messages
    PERFORM VARYING LINE-NUM FROM 15 BY 1 UNTIL LINE-NUM > 20
        DISPLAY SPACES AT LINE LINE-NUM COL 1
    END-PERFORM.
 
EXIT-CONFIRMATION.
    DISPLAY CONFIRMATION-SCREEN.
    ACCEPT CONFIRM-FLAG.
    
    IF CONFIRM-FLAG = 'Y' OR 'y'
        MOVE 4 TO MENU-CHOICE
    ELSE
        *> Clear confirmation message
        DISPLAY SPACES AT LINE 15 COL 1
    END-IF.

Data Entry Form with Field Clearing

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*> Professional data entry form with field management
DATA DIVISION.
WORKING-STORAGE SECTION.
01  CUSTOMER-RECORD.
    05  CUST-ID            PIC 9(6).
    05  CUST-NAME          PIC X(30).
    05  CUST-ADDRESS       PIC X(40).
    05  CUST-PHONE         PIC X(12).
    05  CREDIT-LIMIT       PIC 9(7)V99.
    05  CURRENT-BALANCE    PIC S9(7)V99.
 
01  DISPLAY-FIELDS.
    05  DISP-CREDIT-LIMIT  PIC Z(7).99 BLANK WHEN ZERO.
    05  DISP-BALANCE       PIC Z(7).99- BLANK WHEN ZERO.
 
01  VALIDATION-FLAGS.
    05  VALID-ID           PIC X VALUE 'N'.
    05  VALID-NAME         PIC X VALUE 'N'.
    05  VALID-PHONE        PIC X VALUE 'N'.
 
SCREEN SECTION.
01  CUSTOMER-ENTRY-SCREEN.
    05  BLANK SCREEN.
    05  LINE 2 COL 25 VALUE "CUSTOMER DATA ENTRY".
    05  LINE 4 COL 5  VALUE "Customer ID:".
    05  LINE 4 COL 18 PIC 9(6) TO CUST-ID REQUIRED.
    05  LINE 5 COL 5  VALUE "Name:".
    05  LINE 5 COL 18 PIC X(30) TO CUST-NAME REQUIRED.
    05  LINE 6 COL 5  VALUE "Address:".
    05  LINE 6 COL 18 PIC X(40) TO CUST-ADDRESS.
    05  LINE 7 COL 5  VALUE "Phone:".
    05  LINE 7 COL 18 PIC X(12) TO CUST-PHONE.
    05  LINE 8 COL 5  VALUE "Credit Limit:".
    05  LINE 8 COL 18 PIC Z(7).99 TO CREDIT-LIMIT.
    05  LINE 9 COL 5  VALUE "Current Balance:".
    05  LINE 9 COL 22 FROM DISP-BALANCE.
 
01  VALIDATION-MESSAGES.
    05  LINE 15 COL 5 VALUE "Validation Messages:" FOREGROUND-COLOR 4.
    05  LINE 16 COL 5 PIC X(60) FROM ERROR-MESSAGE FOREGROUND-COLOR 4.
 
PROCEDURE DIVISION.
CUSTOMER-DATA-ENTRY.
    PERFORM UNTIL ALL-DATA-VALID
        PERFORM CLEAR-ENTRY-FIELDS
        PERFORM DISPLAY-ENTRY-FORM
        PERFORM VALIDATE-CUSTOMER-DATA
        
        IF NOT ALL-DATA-VALID
            PERFORM DISPLAY-VALIDATION-ERRORS
            DISPLAY "Press Enter to continue..." AT LINE 20 COL 5
            ACCEPT DUMMY-FIELD
        END-IF
    END-PERFORM.
 
CLEAR-ENTRY-FIELDS.
    MOVE ZEROS TO CUST-ID.
    MOVE SPACES TO CUST-NAME.
    MOVE SPACES TO CUST-ADDRESS.
    MOVE SPACES TO CUST-PHONE.
    MOVE ZEROS TO CREDIT-LIMIT.
    MOVE ZEROS TO CURRENT-BALANCE.
    MOVE SPACES TO ERROR-MESSAGE.
 
DISPLAY-ENTRY-FORM.
    MOVE CREDIT-LIMIT TO DISP-CREDIT-LIMIT.
    MOVE CURRENT-BALANCE TO DISP-BALANCE.
    DISPLAY CUSTOMER-ENTRY-SCREEN.
    ACCEPT CUSTOMER-ENTRY-SCREEN.
 
VALIDATE-CUSTOMER-DATA.
    MOVE 'Y' TO VALID-ID VALID-NAME VALID-PHONE.
    
    IF CUST-ID = ZEROS
        MOVE 'N' TO VALID-ID
        STRING "Customer ID required. " DELIMITED BY SIZE
               INTO ERROR-MESSAGE
        END-STRING
    END-IF.
    
    IF CUST-NAME = SPACES
        MOVE 'N' TO VALID-NAME
        STRING ERROR-MESSAGE DELIMITED BY "  "
               "Customer name required. " DELIMITED BY SIZE
               INTO ERROR-MESSAGE
        END-STRING
    END-IF.
 
DISPLAY-VALIDATION-ERRORS.
    IF ERROR-MESSAGE NOT = SPACES
        DISPLAY VALIDATION-MESSAGES
    END-IF.

Best Practices

Use BLANK WHEN ZERO for professional numeric display formatting
Always clear screens before displaying new content
Provide visual feedback for data entry validation
Use consistent screen layouts across your application
Clear error messages after user acknowledgment
Consider user experience when designing screen flows

Common BLANK Applications

Financial Reports: Hide zero balances and amounts for cleaner presentation
Data Entry Forms: Clear fields between entries for fresh data input
Menu Systems: Clear screens for navigation and user guidance
Error Handling: Clear previous error messages before showing new ones
Status Displays: Show only relevant non-zero status indicators

Frequently Asked Questions

Q: What's the difference between BLANK SCREEN and BLANK LINE?

BLANK SCREEN clears the entire screen before displaying new content, while BLANK LINE clears only a specific line or range of lines. Use BLANK SCREEN for complete screen refreshes and BLANK LINE for selective clearing of specific areas.

Q: How does BLANK WHEN ZERO affect data storage?

BLANK WHEN ZERO only affects display formatting, not data storage. The actual numeric value remains unchanged in memory; only the screen presentation shows blanks instead of zeros. This is purely a visual formatting feature.

Q: Can I use BLANK with all data types?

BLANK WHEN ZERO works with numeric fields only. For character fields, you can move SPACES to clear them, or use screen positioning to display spaces over existing content. The BLANK SCREEN clause works regardless of data types.