What is FROM in COBOL programming?

FROM is a clause used in COBOL for variable control and range specification, primarily with PERFORM VARYING statements. It defines the initial value for a loop control variable, establishing the starting point for iteration and range processing operations.

How do I use FROM with PERFORM VARYING?

Use FROM with PERFORM VARYING by specifying 'PERFORM paragraph-name VARYING variable FROM initial-value BY increment UNTIL condition'. The FROM clause sets the starting value for the control variable before loop execution begins.

What's the difference between FROM and other initialization methods?

FROM provides automatic variable initialization within loop structures, while manual initialization requires separate MOVE statements. FROM ensures the control variable is properly set before loop execution and integrates seamlessly with VARYING clause operations.

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COBOL Tutorial

COBOL FROM Clause

The FROM clause represents a critical variable control and initialization mechanism within COBOL programming structures, serving as the primary specification for defining starting values in loop control variables, range operations, and iterative processing constructs. This clause embodies the principles of controlled variable initialization by providing automatic starting value assignment capabilities, enabling sophisticated range-based processing patterns, and supporting efficient iteration control while maintaining program clarity and ensuring predictable variable state management in enterprise applications that require precise loop control, array processing, and systematic data manipulation operations.

Syntax and Usage

FROM Clause Syntax

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PERFORM paragraph-name 
    VARYING identifier FROM initial-value 
    BY increment-value 
    UNTIL condition
 
PERFORM paragraph-name 
    VARYING identifier FROM literal
    BY literal
    UNTIL identifier > final-value

Variable Control

Initialization

Range Specification

Basic FROM Examples

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IDENTIFICATION DIVISION.
PROGRAM-ID. FROM-CLAUSE-EXAMPLES.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  LOOP-INDEX              PIC 9(3).
01  START-VALUE             PIC 9(3) VALUE 1.
01  END-VALUE               PIC 9(3) VALUE 10.
01  INCREMENT-VALUE         PIC 9(2) VALUE 2.
01  TOTAL-SUM               PIC 9(5) VALUE 0.
 
PROCEDURE DIVISION.
MAIN-PROCESSING.
    *> Basic FROM with literals
    PERFORM SIMPLE-LOOP
        VARYING LOOP-INDEX FROM 1 BY 1
        UNTIL LOOP-INDEX > 5
    
    *> FROM with variables
    PERFORM VARIABLE-LOOP
        VARYING LOOP-INDEX FROM START-VALUE BY INCREMENT-VALUE
        UNTIL LOOP-INDEX > END-VALUE
    
    *> FROM with computed values
    COMPUTE START-VALUE = 10
    COMPUTE END-VALUE = 50
    PERFORM COMPUTED-LOOP
        VARYING LOOP-INDEX FROM START-VALUE BY 5
        UNTIL LOOP-INDEX > END-VALUE
    
    STOP RUN.
 
SIMPLE-LOOP.
    DISPLAY 'Simple loop iteration: ' LOOP-INDEX.
 
VARIABLE-LOOP.
    ADD LOOP-INDEX TO TOTAL-SUM
    DISPLAY 'Variable loop - Index: ' LOOP-INDEX 
            ' Running total: ' TOTAL-SUM.
 
COMPUTED-LOOP.
    DISPLAY 'Computed loop iteration: ' LOOP-INDEX.

Key Features and Benefits

Automatic Initialization

• Sets variable starting value
• Eliminates manual initialization
• Ensures consistent loop setup
• Prevents uninitialized variable errors

Flexible Range Control

• Supports literal and variable values
• Enables dynamic range specification
• Allows computed starting points
• Integrates with increment control

Interactive Tutorial

Hands-On Exercise: Range Processing

Practice using FROM clause for various initialization scenarios

Exercise 1: Array Processing

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01 SALES-DATA OCCURS 12 TIMES.
   05 MONTH-SALES PIC 9(7)V99.
01 MONTH-INDEX PIC 9(2).
01 TOTAL-SALES PIC 9(9)V99 VALUE 0.
 
PROCEDURE DIVISION.
    *> Process all months
    PERFORM CALCULATE-MONTHLY-TOTAL
        VARYING MONTH-INDEX FROM 1 BY 1
        UNTIL MONTH-INDEX > 12.
 
CALCULATE-MONTHLY-TOTAL.
    ADD MONTH-SALES(MONTH-INDEX) TO TOTAL-SALES
    DISPLAY 'Month ' MONTH-INDEX ': $' MONTH-SALES(MONTH-INDEX).

Exercise 2: Range Validation

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01 INPUT-VALUE PIC 9(3).
01 VALID-RANGE-START PIC 9(3) VALUE 100.
01 VALID-RANGE-END PIC 9(3) VALUE 999.
01 CHECK-VALUE PIC 9(3).
 
PROCEDURE DIVISION.
    *> Validate input against range
    PERFORM CHECK-RANGE-VALUE
        VARYING CHECK-VALUE FROM VALID-RANGE-START BY 1
        UNTIL CHECK-VALUE > VALID-RANGE-END
           OR CHECK-VALUE = INPUT-VALUE.
 
CHECK-RANGE-VALUE.
    IF CHECK-VALUE = INPUT-VALUE
        DISPLAY 'Input value ' INPUT-VALUE ' is valid'
        EXIT PARAGRAPH
    END-IF.

Advanced FROM Patterns

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IDENTIFICATION DIVISION.
PROGRAM-ID. ADVANCED-FROM-PATTERNS.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  MATRIX-DIMENSIONS.
    05  ROWS                PIC 9(2) VALUE 10.
    05  COLS                PIC 9(2) VALUE 8.
01  ROW-INDEX               PIC 9(2).
01  COL-INDEX               PIC 9(2).
01  DATA-MATRIX OCCURS 10 TIMES.
    05  MATRIX-ROW OCCURS 8 TIMES.
        10  CELL-VALUE      PIC 9(5).
 
01  PROCESSING-RANGE.
    05  START-ROW           PIC 9(2) VALUE 3.
    05  END-ROW             PIC 9(2) VALUE 7.
    05  START-COL           PIC 9(2) VALUE 2.
    05  END-COL             PIC 9(2) VALUE 6.
 
PROCEDURE DIVISION.
MAIN-PROCESSING.
    *> Initialize entire matrix
    PERFORM INITIALIZE-MATRIX-ROW
        VARYING ROW-INDEX FROM 1 BY 1
        UNTIL ROW-INDEX > ROWS
    
    *> Process specific range
    PERFORM PROCESS-RANGE-ROW
        VARYING ROW-INDEX FROM START-ROW BY 1
        UNTIL ROW-INDEX > END-ROW
    
    STOP RUN.
 
INITIALIZE-MATRIX-ROW.
    PERFORM INITIALIZE-MATRIX-CELL
        VARYING COL-INDEX FROM 1 BY 1
        UNTIL COL-INDEX > COLS.
 
INITIALIZE-MATRIX-CELL.
    COMPUTE CELL-VALUE(ROW-INDEX, COL-INDEX) = 
        ROW-INDEX * 10 + COL-INDEX.
 
PROCESS-RANGE-ROW.
    DISPLAY 'Processing row ' ROW-INDEX
    PERFORM PROCESS-RANGE-CELL
        VARYING COL-INDEX FROM START-COL BY 1
        UNTIL COL-INDEX > END-COL.
 
PROCESS-RANGE-CELL.
    MULTIPLY CELL-VALUE(ROW-INDEX, COL-INDEX) BY 2
    DISPLAY 'Cell [' ROW-INDEX ',' COL-INDEX '] = ' 
            CELL-VALUE(ROW-INDEX, COL-INDEX).

Best Practices

Knowledge Check

Test Your Understanding

Question 1: Basic Syntax

What's the correct syntax to start a loop from value 5?

Answer: PERFORM paragraph-name VARYING variable FROM 5 BY increment UNTIL condition

Question 2: Variable Usage

Can you use a variable instead of a literal in the FROM clause?

Answer: Yes, you can use variables in FROM clauses: PERFORM paragraph VARYING counter FROM start-variable BY increment UNTIL condition.

Question 3: Initialization Timing

When is the FROM value assigned to the control variable?

Answer: The FROM value is assigned to the control variable before the first iteration of the loop begins, ensuring proper initialization.

Common Patterns

Sequential Processing

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01 RECORD-TABLE OCCURS 1000 TIMES.
   05 RECORD-DATA PIC X(80).
01 INDEX-VAR PIC 9(4).
 
PROCEDURE DIVISION.
    PERFORM PROCESS-RECORD
        VARYING INDEX-VAR FROM 1 BY 1
        UNTIL INDEX-VAR > 1000.
 
PROCESS-RECORD.
    *> Process RECORD-DATA(INDEX-VAR)
    CONTINUE.

Range Validation

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01 MIN-VALUE PIC 9(3) VALUE 100.
01 MAX-VALUE PIC 9(3) VALUE 999.
01 TEST-VALUE PIC 9(3).
01 VALID-FLAG PIC X VALUE 'N'.
 
PROCEDURE DIVISION.
    PERFORM CHECK-VALIDITY
        VARYING TEST-VALUE FROM MIN-VALUE BY 1
        UNTIL TEST-VALUE > MAX-VALUE
           OR VALID-FLAG = 'Y'.

COBOL Tutorial

COBOL FROM Clause

Syntax and Usage

Basic FROM Examples

Key Features and Benefits

Interactive Tutorial

Exercise 1: Array Processing

Exercise 2: Range Validation

Advanced FROM Patterns

Best Practices

Knowledge Check

Question 1: Basic Syntax

Question 2: Variable Usage

Question 3: Initialization Timing

Common Patterns

Frequently Asked Questions

Related Concepts

Variable Control

Loop Initialization

Range Processing

Related Pages

COBOL Tutorial

COBOL FROM Clause

Syntax and Usage

Basic FROM Examples

Key Features and Benefits

Interactive Tutorial

Exercise 1: Array Processing

Exercise 2: Range Validation

Advanced FROM Patterns

Best Practices

Proper Initialization

Range Design

Performance Optimization

Knowledge Check

Question 1: Basic Syntax

Question 2: Variable Usage

Question 3: Initialization Timing

Common Patterns

Frequently Asked Questions

Can I use negative values in FROM clauses?

What happens if the FROM value equals the UNTIL condition initially?

Can I modify the FROM variable during loop execution?

How does FROM work with nested loops?

Related Concepts

Variable Control

Loop Initialization

Range Processing

Related Pages