COBOL DOWN Keyword

Master screen positioning and cursor movement with the DOWN keyword for effective terminal-based user interface development in COBOL applications.

Overview

The DOWN keyword in COBOL is used for screen positioning and cursor movement in terminal-based applications. It provides precise control over vertical positioning, allowing programs to move the cursor or screen position downward by a specified number of lines. This functionality is essential for creating interactive user interfaces, forms, and screen-based applications in mainframe environments.

DOWN is particularly valuable in environments like CICS (Customer Information Control System), IMS (Information Management System), and other transaction processing systems where screen control is crucial for user interaction. It enables developers to create sophisticated terminal interfaces with precise positioning control.

Understanding DOWN and its applications is fundamental for developing professional mainframe applications that require user-friendly interfaces, data entry forms, and interactive menus. It works in conjunction with other positioning keywords to provide comprehensive screen control capabilities.

Basic DOWN Syntax and Usage

Simple DOWN Movement

The basic syntax for DOWN involves specifying the number of lines to move:

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       DISPLAY "Current Position" AT LINE 10 COL 20
       DISPLAY "Moved Down" DOWN 3 LINES
       DISPLAY "Further Down" DOWN 2

This example demonstrates moving the cursor down from its current position. The first DISPLAY establishes a starting position, then subsequent displays move progressively downward.

DOWN with Numeric Variables

DOWN can use variables to specify dynamic positioning:

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       WORKING-STORAGE SECTION.
       01  WS-LINE-OFFSET      PIC 9(2) VALUE 5.
       01  WS-MENU-SPACING     PIC 9(1) VALUE 2.
       
       PROCEDURE DIVISION.
       DISPLAY-MENU.
           DISPLAY "MAIN MENU" AT LINE 5 COL 30
           DISPLAY "1. Customer Entry" DOWN WS-MENU-SPACING
           DISPLAY "2. Order Processing" DOWN WS-MENU-SPACING
           DISPLAY "3. Reports" DOWN WS-MENU-SPACING.

Using variables with DOWN provides flexibility for adjusting screen layouts dynamically based on program logic or user preferences.

Screen Positioning Applications

Menu Creation

DOWN is commonly used to create well-formatted menus:

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       DISPLAY-MAIN-MENU.
           DISPLAY SPACES WITH BLANK SCREEN
           DISPLAY "╔══════════════════════════════════╗" 
                   AT LINE 5 COL 25
           DISPLAY "║        CUSTOMER SYSTEM           ║" 
                   DOWN 1
           DISPLAY "║                                  ║" 
                   DOWN 1
           DISPLAY "║  1. Add New Customer             ║" 
                   DOWN 1
           DISPLAY "║  2. Update Customer              ║" 
                   DOWN 1
           DISPLAY "║  3. Delete Customer              ║" 
                   DOWN 1
           DISPLAY "║  4. Customer Reports             ║" 
                   DOWN 1
           DISPLAY "║  5. Exit System                  ║" 
                   DOWN 1
           DISPLAY "║                                  ║" 
                   DOWN 1
           DISPLAY "╚══════════════════════════════════╝" 
                   DOWN 1.

This creates a professional-looking menu with consistent spacing using DOWN for vertical positioning.

Form Layout Design

DOWN helps create organized data entry forms:

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       DISPLAY-CUSTOMER-FORM.
           DISPLAY SPACES WITH BLANK SCREEN
           DISPLAY "CUSTOMER INFORMATION ENTRY" 
                   AT LINE 3 COL 25
           
           DISPLAY "Customer ID     : " 
                   AT LINE 6 COL 10
           DISPLAY "Customer Name   : " 
                   DOWN 2
           DISPLAY "Address Line 1  : " 
                   DOWN 2
           DISPLAY "Address Line 2  : " 
                   DOWN 2
           DISPLAY "City            : " 
                   DOWN 2
           DISPLAY "State           : " 
                   DOWN 2
           DISPLAY "ZIP Code        : " 
                   DOWN 2
           DISPLAY "Phone Number    : " 
                   DOWN 2.

This form uses DOWN to create consistent spacing between input fields, making the form easy to read and navigate.

Advanced DOWN Techniques

Conditional Positioning

DOWN can be used conditionally based on program logic:

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       WORKING-STORAGE SECTION.
       01  WS-ERROR-FLAG       PIC X(1) VALUE "N".
       01  WS-ERROR-COUNT      PIC 9(2) VALUE ZERO.
       01  WS-CURRENT-LINE     PIC 9(2) VALUE 10.
       
       PROCEDURE DIVISION.
       DISPLAY-MESSAGES.
           DISPLAY "Processing Status:" AT LINE WS-CURRENT-LINE COL 10
           
           IF WS-ERROR-FLAG = "Y"
               ADD 2 TO WS-CURRENT-LINE
               DISPLAY "ERROR: Invalid input detected" 
                       DOWN 2 WITH FOREGROUND-COLOR RED
               ADD 1 TO WS-ERROR-COUNT
           ELSE
               DISPLAY "Processing completed successfully" 
                       DOWN 2 WITH FOREGROUND-COLOR GREEN
           END-IF.

This example shows conditional use of DOWN based on error conditions, creating dynamic screen layouts.

Scrolling and Pagination

DOWN can be used to implement scrolling functionality:

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       WORKING-STORAGE SECTION.
       01  WS-PAGE-SIZE        PIC 9(2) VALUE 15.
       01  WS-CURRENT-ROW      PIC 9(2) VALUE 1.
       01  WS-RECORDS-SHOWN    PIC 9(2) VALUE ZERO.
       01  WS-START-LINE       PIC 9(2) VALUE 5.
       
       PROCEDURE DIVISION.
       DISPLAY-PAGE.
           MOVE WS-START-LINE TO WS-CURRENT-ROW
           MOVE ZERO TO WS-RECORDS-SHOWN
           
           PERFORM UNTIL WS-RECORDS-SHOWN >= WS-PAGE-SIZE
               OR END-OF-FILE
               
               PERFORM READ-NEXT-RECORD
               IF NOT END-OF-FILE
                   DISPLAY CUSTOMER-RECORD 
                           AT LINE WS-CURRENT-ROW COL 5
                   ADD 1 TO WS-CURRENT-ROW
                   ADD 1 TO WS-RECORDS-SHOWN
               END-IF
           END-PERFORM
           
           DISPLAY "Press ENTER for next page..." 
                   DOWN 2 WITH HIGHLIGHT.

This creates a pagination system using DOWN for consistent record positioning and page navigation.

CICS Integration with DOWN

CICS Screen Handling

In CICS environments, DOWN works with map definitions and screen control:

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       WORKING-STORAGE SECTION.
       01  WS-MAP-FIELDS.
           05  WS-CURSOR-POS.
               10  WS-CURSOR-LINE  PIC 9(2) VALUE 10.
               10  WS-CURSOR-COL   PIC 9(2) VALUE 20.
       
       PROCEDURE DIVISION.
       SEND-CUSTOMER-MAP.
           EXEC CICS SEND MAP('CUSTMAP')
                MAPSET('CUSTSET')
                CURSOR(WS-CURSOR-POS)
                ERASE
           END-EXEC
           
           * Position for error messages
           IF EIBRESP = DFHRESP(NORMAL)
               DISPLAY "Customer data sent successfully"
                       AT LINE 20 COL 10
           ELSE
               DISPLAY "Error sending customer map"
                       DOWN 2 WITH FOREGROUND-COLOR RED
               DISPLAY "Please contact system administrator"
                       DOWN 1
           END-IF.

This example shows how DOWN can be used in conjunction with CICS commands for screen positioning.

Interactive Field Navigation

DOWN helps create logical field navigation patterns:

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       FIELD-NAVIGATION.
           EVALUATE WS-CURRENT-FIELD
               WHEN "CUSTID"
                   MOVE "CUSTNAME" TO WS-CURRENT-FIELD
                   DISPLAY CURSOR AT LINE 8 COL 25
               WHEN "CUSTNAME"
                   MOVE "ADDRESS1" TO WS-CURRENT-FIELD
                   DISPLAY CURSOR DOWN 2
               WHEN "ADDRESS1"
                   MOVE "ADDRESS2" TO WS-CURRENT-FIELD
                   DISPLAY CURSOR DOWN 2
               WHEN "ADDRESS2"
                   MOVE "CITY" TO WS-CURRENT-FIELD
                   DISPLAY CURSOR DOWN 2
               WHEN OTHER
                   MOVE "CUSTID" TO WS-CURRENT-FIELD
                   DISPLAY CURSOR AT LINE 6 COL 25
           END-EVALUATE.

This creates a logical tab order using DOWN to move between form fields in a predictable pattern.

Error Handling and Validation

Error Message Positioning

DOWN is useful for positioning error messages consistently:

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       WORKING-STORAGE SECTION.
       01  WS-ERROR-LINE       PIC 9(2) VALUE 22.
       01  WS-ERROR-MESSAGES.
           05  WS-ERR-REQUIRED PIC X(30) VALUE
               "* Required field missing".
           05  WS-ERR-INVALID  PIC X(30) VALUE
               "* Invalid data format".
           05  WS-ERR-DUPLICATE PIC X(30) VALUE
               "* Duplicate entry found".
       
       PROCEDURE DIVISION.
       VALIDATE-INPUT.
           * Clear error area first
           DISPLAY SPACES AT LINE WS-ERROR-LINE COL 1
           
           IF CUST-ID = SPACES
               DISPLAY WS-ERR-REQUIRED 
                       AT LINE WS-ERROR-LINE COL 10
                       WITH FOREGROUND-COLOR RED
               ADD 1 TO WS-ERROR-LINE
           END-IF
           
           IF CUST-NAME = SPACES
               DISPLAY WS-ERR-REQUIRED 
                       DOWN 1 WITH FOREGROUND-COLOR RED
               ADD 1 TO WS-ERROR-LINE
           END-IF
           
           IF NOT VALID-ZIP-CODE
               DISPLAY WS-ERR-INVALID 
                       DOWN 1 WITH FOREGROUND-COLOR RED
           END-IF.

This approach uses DOWN to stack error messages vertically, creating a clear error display area.

Validation Feedback

DOWN can provide immediate validation feedback:

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       REAL-TIME-VALIDATION.
           PERFORM VALIDATE-CUSTOMER-ID
           IF VALIDATION-ERROR
               DISPLAY "✗ Invalid Customer ID format" 
                       DOWN 1 WITH FOREGROUND-COLOR RED
               DISPLAY "  Use format: CUST-99999" 
                       DOWN 1
           ELSE
               DISPLAY "✓ Customer ID valid" 
                       DOWN 1 WITH FOREGROUND-COLOR GREEN
           END-IF
           
           PERFORM VALIDATE-PHONE-NUMBER
           IF VALIDATION-ERROR
               DISPLAY "✗ Invalid phone number" 
                       DOWN 1 WITH FOREGROUND-COLOR RED
               DISPLAY "  Use format: (999) 999-9999" 
                       DOWN 1
           ELSE
               DISPLAY "✓ Phone number valid" 
                       DOWN 1 WITH FOREGROUND-COLOR GREEN
           END-IF.

This provides immediate visual feedback using DOWN to position validation messages next to input fields.

Performance and Best Practices

Efficient Screen Updates

Optimize screen updates when using DOWN extensively:

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       WORKING-STORAGE SECTION.
       01  WS-SCREEN-BUFFER.
           05  WS-BUFFER-LINES OCCURS 24 TIMES.
               10  WS-LINE-DATA    PIC X(80).
       01  WS-CURRENT-LINE     PIC 9(2) VALUE 1.
       
       PROCEDURE DIVISION.
       BUILD-SCREEN-BUFFER.
           * Build entire screen in memory first
           MOVE "CUSTOMER REPORT" TO WS-LINE-DATA(5)
           MOVE ALL "-" TO WS-LINE-DATA(6)
           
           PERFORM VARYING WS-RECORD-COUNT FROM 1 BY 1
               UNTIL WS-RECORD-COUNT > 15
               
               ADD 2 TO WS-CURRENT-LINE
               STRING CUST-ID(WS-RECORD-COUNT) " "
                      CUST-NAME(WS-RECORD-COUNT) " "
                      CUST-BALANCE(WS-RECORD-COUNT)
                      INTO WS-LINE-DATA(WS-CURRENT-LINE)
           END-PERFORM
           
           * Display entire screen at once
           PERFORM DISPLAY-SCREEN-BUFFER.
           
       DISPLAY-SCREEN-BUFFER.
           DISPLAY SPACES WITH BLANK SCREEN
           PERFORM VARYING WS-CURRENT-LINE FROM 1 BY 1
               UNTIL WS-CURRENT-LINE > 24
               
               IF WS-LINE-DATA(WS-CURRENT-LINE) NOT = SPACES
                   DISPLAY WS-LINE-DATA(WS-CURRENT-LINE)
                           AT LINE WS-CURRENT-LINE COL 1
               END-IF
           END-PERFORM.

This approach builds the entire screen in memory before displaying, reducing screen flicker and improving performance.

Memory Management

Manage screen positioning variables efficiently:

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       WORKING-STORAGE SECTION.
       01  WS-SCREEN-CONTROL.
           05  WS-SCREEN-LIMITS.
               10  WS-MAX-LINES    PIC 9(2) VALUE 24.
               10  WS-MAX-COLS     PIC 9(2) VALUE 80.
               10  WS-MIN-LINE     PIC 9(2) VALUE 1.
               10  WS-MIN-COL      PIC 9(2) VALUE 1.
           05  WS-CURRENT-POS.
               10  WS-CURR-LINE    PIC 9(2) VALUE 1.
               10  WS-CURR-COL     PIC 9(2) VALUE 1.
       
       PROCEDURE DIVISION.
       SAFE-DOWN-MOVEMENT.
           IF WS-CURR-LINE + WS-DOWN-AMOUNT <= WS-MAX-LINES
               ADD WS-DOWN-AMOUNT TO WS-CURR-LINE
               DISPLAY WS-MESSAGE AT LINE WS-CURR-LINE COL WS-CURR-COL
           ELSE
               PERFORM SCROLL-SCREEN-UP
               DISPLAY WS-MESSAGE AT LINE WS-MAX-LINES COL WS-CURR-COL
           END-IF.

This ensures safe cursor movement that respects screen boundaries and handles overflow conditions.

Hands-on Exercise

Exercise: Interactive Menu System

Create an interactive menu system using DOWN for positioning that includes error handling and user navigation.

Requirements:

Create a main menu with at least 5 options using DOWN for spacing
Implement error messages positioned with DOWN
Include input validation with positioned feedback
Use DOWN for creating consistent screen layouts
Handle screen boundary conditions safely

View Solution

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       WORKING-STORAGE SECTION.
       01  WS-MENU-CONTROL.
           05  WS-USER-CHOICE      PIC X(1).
           05  WS-VALID-CHOICE     PIC X(1) VALUE "N".
           05  WS-EXIT-FLAG        PIC X(1) VALUE "N".
           
       01  WS-SCREEN-POSITIONS.
           05  WS-TITLE-LINE       PIC 9(2) VALUE 3.
           05  WS-MENU-START       PIC 9(2) VALUE 7.
           05  WS-PROMPT-LINE      PIC 9(2) VALUE 15.
           05  WS-ERROR-LINE       PIC 9(2) VALUE 17.
           
       PROCEDURE DIVISION.
       MAIN-MENU-LOOP.
           PERFORM UNTIL WS-EXIT-FLAG = "Y"
               PERFORM DISPLAY-MAIN-MENU
               PERFORM GET-USER-CHOICE
               PERFORM VALIDATE-CHOICE
               IF WS-VALID-CHOICE = "Y"
                   PERFORM PROCESS-MENU-CHOICE
               ELSE
                   PERFORM DISPLAY-ERROR-MESSAGE
               END-IF
           END-PERFORM
           GOBACK.
           
       DISPLAY-MAIN-MENU.
           DISPLAY SPACES WITH BLANK SCREEN
           DISPLAY "═══════════════════════════════════" 
                   AT LINE WS-TITLE-LINE COL 25
           DISPLAY "        INVENTORY SYSTEM          " 
                   DOWN 1
           DISPLAY "═══════════════════════════════════" 
                   DOWN 1
           
           DISPLAY "1. Add New Item" 
                   AT LINE WS-MENU-START COL 30
           DISPLAY "2. Update Item" 
                   DOWN 2
           DISPLAY "3. Delete Item" 
                   DOWN 2
           DISPLAY "4. Search Items" 
                   DOWN 2
           DISPLAY "5. Generate Reports" 
                   DOWN 2
           DISPLAY "6. Exit System" 
                   DOWN 2
           
           DISPLAY "Enter your choice (1-6): " 
                   AT LINE WS-PROMPT-LINE COL 25 
                   WITH NO ADVANCING.
                   
       GET-USER-CHOICE.
           ACCEPT WS-USER-CHOICE
           DISPLAY SPACES AT LINE WS-ERROR-LINE COL 1.
           
       VALIDATE-CHOICE.
           IF WS-USER-CHOICE >= "1" AND WS-USER-CHOICE <= "6"
               MOVE "Y" TO WS-VALID-CHOICE
           ELSE
               MOVE "N" TO WS-VALID-CHOICE
           END-IF.
           
       DISPLAY-ERROR-MESSAGE.
           DISPLAY "✗ Invalid choice. Please enter 1-6." 
                   AT LINE WS-ERROR-LINE COL 25
                   WITH FOREGROUND-COLOR RED
           DISPLAY "Press ENTER to continue..." 
                   DOWN 1 WITH HIGHLIGHT
           ACCEPT WS-USER-CHOICE.
           
       PROCESS-MENU-CHOICE.
           EVALUATE WS-USER-CHOICE
               WHEN "1"
                   PERFORM ADD-NEW-ITEM
               WHEN "2"
                   PERFORM UPDATE-ITEM
               WHEN "3"
                   PERFORM DELETE-ITEM
               WHEN "4"
                   PERFORM SEARCH-ITEMS
               WHEN "5"
                   PERFORM GENERATE-REPORTS
               WHEN "6"
                   MOVE "Y" TO WS-EXIT-FLAG
                   DISPLAY "Thank you for using Inventory System" 
                           AT LINE 20 COL 25
                           WITH FOREGROUND-COLOR GREEN
                   DISPLAY "System shutting down..." 
                           DOWN 2
           END-EVALUATE.
           
       ADD-NEW-ITEM.
           DISPLAY SPACES WITH BLANK SCREEN
           DISPLAY "ADD NEW INVENTORY ITEM" 
                   AT LINE 3 COL 30
           DISPLAY "Item Code    : " 
                   AT LINE 6 COL 20
           DISPLAY "Description  : " 
                   DOWN 2
           DISPLAY "Quantity     : " 
                   DOWN 2
           DISPLAY "Unit Price   : " 
                   DOWN 2
           DISPLAY "Category     : " 
                   DOWN 2
           
           DISPLAY "Press ENTER when complete..." 
                   DOWN 3 WITH HIGHLIGHT
           ACCEPT WS-USER-CHOICE.

COBOL DOWN Keyword

Overview

Basic DOWN Syntax and Usage

Simple DOWN Movement

DOWN with Numeric Variables

Screen Positioning Applications

Menu Creation

Form Layout Design

Advanced DOWN Techniques

Conditional Positioning

Scrolling and Pagination

CICS Integration with DOWN

CICS Screen Handling

Interactive Field Navigation

Error Handling and Validation

Error Message Positioning

Validation Feedback

Performance and Best Practices

Efficient Screen Updates

Memory Management

Hands-on Exercise

Exercise: Interactive Menu System

Requirements:

Quiz

Test Your Knowledge

Frequently Asked Questions

Related Pages

Related Concepts

Screen Handling

CICS Programming

Terminal Operations

User Interface Design