What are class conditions in COBOL?

Class conditions in COBOL are tests that check whether a data item contains characters of a specific class (type). The main class conditions are IS NUMERIC (checks if all characters are digits), IS ALPHABETIC (checks if all characters are letters), and IS ALPHANUMERIC (checks if all characters are letters or digits). Class conditions are used for data validation, input verification, and ensuring data meets expected format requirements before processing.

What does IS NUMERIC check in COBOL?

IS NUMERIC checks if all characters in a data item are numeric digits (0-9). It returns true if every character in the field is a digit, and false if any character is not a digit (including spaces, letters, or special characters). IS NUMERIC is useful for validating that input data contains only numbers, checking if a field can be used in numeric operations, and ensuring data format correctness before numeric processing.

What does IS ALPHABETIC check in COBOL?

IS ALPHABETIC checks if all characters in a data item are alphabetic letters (A-Z, a-z, and sometimes space depending on implementation). It returns true if every character is a letter (and possibly spaces), and false if any character is a digit or special character. IS ALPHABETIC is useful for validating names, text fields, and ensuring data contains only letters before alphabetic processing.

What does IS ALPHANUMERIC check in COBOL?

IS ALPHANUMERIC checks if all characters in a data item are alphanumeric (letters A-Z, a-z, or digits 0-9). It returns true if every character is either a letter or a digit, and false if any character is a special character or space (depending on implementation). IS ALPHANUMERIC is useful for validating identifiers, codes, and fields that should contain only letters and numbers.

How do you use class conditions in IF statements?

You use class conditions in IF statements like: IF data-item IS NUMERIC, IF data-item IS ALPHABETIC, or IF data-item IS ALPHANUMERIC. You can also use NOT: IF data-item IS NOT NUMERIC. Class conditions return true or false, allowing you to branch based on the data type. Example: IF ZIP-CODE IS NUMERIC, then process as numeric, ELSE display error message.

What is the difference between IS NUMERIC and checking for digits?

IS NUMERIC is a built-in class condition that efficiently checks if all characters are digits. It's more efficient and clearer than manually checking each character. IS NUMERIC handles the entire field at once and is optimized by the compiler. Manual checking would require looping through each character, which is slower and more error-prone. IS NUMERIC is the standard, recommended way to validate numeric data.

Can you use class conditions with NOT?

Yes, you can use NOT with class conditions: IS NOT NUMERIC, IS NOT ALPHABETIC, IS NOT ALPHANUMERIC. NOT inverts the condition, so IS NOT NUMERIC returns true if the field contains any non-numeric characters. This is useful for error checking: IF INPUT-FIELD IS NOT NUMERIC, then display error message.

How do class conditions handle spaces?

Class condition behavior with spaces varies by implementation. Generally, IS NUMERIC returns false if spaces are present (spaces are not numeric). IS ALPHABETIC may treat spaces as valid (depending on compiler), allowing fields with letters and spaces. IS ALPHANUMERIC typically returns false if spaces are present. Always test with your specific compiler to understand exact behavior. For strict validation, you may need to trim spaces first or use additional checks.

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COBOL Class Conditions

Class conditions in COBOL are tests that check whether a data item contains characters of a specific class (type). The main class conditions are IS NUMERIC (checks for digits), IS ALPHABETIC (checks for letters), and IS ALPHANUMERIC (checks for letters or digits). Class conditions are essential for data validation, input verification, and ensuring data meets expected format requirements before processing in mainframe COBOL programs.

What are Class Conditions?

Class conditions test the character class (type) of data:

IS NUMERIC: Checks if all characters are digits (0-9)
IS ALPHABETIC: Checks if all characters are letters (A-Z, a-z)
IS ALPHANUMERIC: Checks if all characters are letters or digits
IS NOT: Inverts any class condition

Class conditions return true or false, allowing conditional processing based on data type.

IS NUMERIC Condition

IS NUMERIC checks if all characters in a field are numeric digits:

IS NUMERIC Syntax

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       IF data-item IS NUMERIC
           imperative-statement
       END-IF
       
       *> Or with NOT
       IF data-item IS NOT NUMERIC
           imperative-statement
       END-IF

Example: Validating Numeric Input

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       WORKING-STORAGE SECTION.
       01  ZIP-CODE        PIC X(10).
       01  PHONE-NUMBER    PIC X(14).
       01  AMOUNT-INPUT    PIC X(15).
       
       PROCEDURE DIVISION.
       MAIN-PARA.
           *> Validate ZIP code
           ACCEPT ZIP-CODE
           IF ZIP-CODE IS NUMERIC
               DISPLAY "Valid ZIP code: " ZIP-CODE
               *> Process as numeric
           ELSE
               DISPLAY "ERROR: ZIP code must be numeric"
               DISPLAY "Invalid value: " ZIP-CODE
           END-IF
           
           *> Validate phone number (digits only, no formatting)
           ACCEPT PHONE-NUMBER
           IF PHONE-NUMBER IS NUMERIC
               DISPLAY "Valid phone number: " PHONE-NUMBER
           ELSE
               DISPLAY "ERROR: Phone number contains non-numeric characters"
           END-IF
           
           *> Validate amount
           ACCEPT AMOUNT-INPUT
           IF AMOUNT-INPUT IS NOT NUMERIC
               DISPLAY "ERROR: Amount must be numeric"
               DISPLAY "Invalid amount: " AMOUNT-INPUT
           END-IF
           
           STOP RUN.

IS NUMERIC returns true only if every character is a digit (0-9). Spaces, letters, or special characters cause it to return false.

Important Notes about IS NUMERIC

All characters must be digits: Even one non-digit character makes IS NUMERIC false
Spaces are not numeric: Fields with spaces return false
Leading zeros are valid: "000123" is numeric
No decimal points: "123.45" is NOT numeric (contains a period)
No signs: "+123" or "-123" are NOT numeric (contains + or -)

IS ALPHABETIC Condition

IS ALPHABETIC checks if all characters are letters:

IS ALPHABETIC Syntax

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       IF data-item IS ALPHABETIC
           imperative-statement
       END-IF
       
       *> Or with NOT
       IF data-item IS NOT ALPHABETIC
           imperative-statement
       END-IF

Example: Validating Names

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       WORKING-STORAGE SECTION.
       01  FIRST-NAME      PIC X(30).
       01  LAST-NAME       PIC X(30).
       01  STATE-CODE      PIC X(2).
       
       PROCEDURE DIVISION.
       MAIN-PARA.
           *> Validate first name
           ACCEPT FIRST-NAME
           IF FIRST-NAME IS ALPHABETIC
               DISPLAY "Valid first name: " FIRST-NAME
           ELSE
               DISPLAY "ERROR: First name must contain only letters"
               DISPLAY "Invalid name: " FIRST-NAME
           END-IF
           
           *> Validate last name
           ACCEPT LAST-NAME
           IF LAST-NAME IS NOT ALPHABETIC
               DISPLAY "ERROR: Last name contains invalid characters"
           END-IF
           
           *> Validate state code (letters only)
           ACCEPT STATE-CODE
           IF STATE-CODE IS ALPHABETIC
               DISPLAY "Valid state code: " STATE-CODE
           ELSE
               DISPLAY "ERROR: State code must be letters only"
           END-IF
           
           STOP RUN.

IS ALPHABETIC returns true if all characters are letters (A-Z, a-z). Behavior with spaces may vary by compiler - some treat spaces as valid, others do not.

IS ALPHANUMERIC Condition

IS ALPHANUMERIC checks if all characters are letters or digits:

IS ALPHANUMERIC Syntax

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       IF data-item IS ALPHANUMERIC
           imperative-statement
       END-IF
       
       *> Or with NOT
       IF data-item IS NOT ALPHANUMERIC
           imperative-statement
       END-IF

Example: Validating Codes and IDs

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       WORKING-STORAGE SECTION.
       01  CUSTOMER-ID     PIC X(10).
       01  PRODUCT-CODE    PIC X(8).
       01  ACCOUNT-NUMBER  PIC X(12).
       
       PROCEDURE DIVISION.
       MAIN-PARA.
           *> Validate customer ID (letters and numbers only)
           ACCEPT CUSTOMER-ID
           IF CUSTOMER-ID IS ALPHANUMERIC
               DISPLAY "Valid customer ID: " CUSTOMER-ID
           ELSE
               DISPLAY "ERROR: Customer ID must be alphanumeric"
               DISPLAY "No special characters allowed"
           END-IF
           
           *> Validate product code
           ACCEPT PRODUCT-CODE
           IF PRODUCT-CODE IS NOT ALPHANUMERIC
               DISPLAY "ERROR: Product code contains invalid characters"
           END-IF
           
           *> Validate account number
           ACCEPT ACCOUNT-NUMBER
           IF ACCOUNT-NUMBER IS ALPHANUMERIC
               DISPLAY "Valid account number: " ACCOUNT-NUMBER
           ELSE
               DISPLAY "ERROR: Account number must be alphanumeric"
           END-IF
           
           STOP RUN.

IS ALPHANUMERIC returns true if all characters are either letters (A-Z, a-z) or digits (0-9). Special characters, spaces, or punctuation cause it to return false.

Using Class Conditions in Conditional Statements

Class conditions can be used in various conditional statements:

With IF Statements

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       IF INPUT-FIELD IS NUMERIC
           *> Process as numeric
           MOVE INPUT-FIELD TO NUMERIC-FIELD
           PERFORM NUMERIC-PROCESSING
       ELSE
           *> Handle non-numeric input
           DISPLAY "ERROR: Expected numeric value"
           PERFORM ERROR-HANDLING
       END-IF

With EVALUATE Statements

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       EVALUATE TRUE
           WHEN INPUT-FIELD IS NUMERIC
               PERFORM PROCESS-NUMERIC
           WHEN INPUT-FIELD IS ALPHABETIC
               PERFORM PROCESS-TEXT
           WHEN INPUT-FIELD IS ALPHANUMERIC
               PERFORM PROCESS-CODE
           WHEN OTHER
               DISPLAY "ERROR: Invalid character type"
               PERFORM ERROR-HANDLING
       END-EVALUATE

With Logical Operators

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       *> Multiple conditions
       IF ZIP-CODE IS NUMERIC
          AND LENGTH OF ZIP-CODE = 5
           DISPLAY "Valid 5-digit ZIP code"
       END-IF
       
       *> Complex validation
       IF CUSTOMER-ID IS ALPHANUMERIC
          AND CUSTOMER-ID NOT = SPACES
          AND LENGTH OF CUSTOMER-ID >= 5
           PERFORM PROCESS-CUSTOMER
       ELSE
           DISPLAY "Invalid customer ID format"
       END-IF

Data Validation Patterns

Common patterns for using class conditions in validation:

Pattern 1: Input Validation

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       ACCEPT USER-INPUT
       IF USER-INPUT IS NUMERIC
           MOVE USER-INPUT TO NUMERIC-FIELD
           PERFORM PROCESS-NUMERIC
       ELSE
           DISPLAY "ERROR: Numeric input required"
           DISPLAY "You entered: " USER-INPUT
           PERFORM REQUEST-INPUT-AGAIN
       END-IF

Pattern 2: Format Validation

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       *> Validate format before processing
       IF ACCOUNT-CODE IS ALPHANUMERIC
          AND LENGTH OF ACCOUNT-CODE = 8
           PERFORM PROCESS-ACCOUNT
       ELSE
           DISPLAY "ERROR: Account code must be 8 alphanumeric characters"
       END-IF

Pattern 3: Type-Specific Processing

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       *> Route to appropriate processor based on type
       IF DATA-FIELD IS NUMERIC
           PERFORM NUMERIC-PROCESSOR
       ELSE IF DATA-FIELD IS ALPHABETIC
           PERFORM TEXT-PROCESSOR
       ELSE IF DATA-FIELD IS ALPHANUMERIC
           PERFORM CODE-PROCESSOR
       ELSE
           DISPLAY "ERROR: Invalid data type"
           PERFORM ERROR-HANDLER
       END-IF

Class Condition Behavior with Spaces

Understanding how class conditions handle spaces:

Class Condition Behavior with Spaces
Condition	Field with Spaces	Description
IS NUMERIC	Returns FALSE	Spaces are not numeric digits, so fields with spaces fail the numeric test
IS ALPHABETIC	Varies by compiler	Some compilers allow spaces in alphabetic fields, others do not
IS ALPHANUMERIC	Returns FALSE	Spaces are not letters or digits, so fields with spaces fail the test

For strict validation, consider trimming spaces before testing, or use additional validation logic.

Best Practices for Class Conditions

Follow these best practices:

Validate before processing: Use class conditions to validate input before performing operations
Provide clear error messages: When validation fails, explain what was expected
Test edge cases: Test with empty fields, spaces, special characters, and boundary values
Combine with length checks: Often combine class conditions with length validation
Understand compiler behavior: Test space handling with your specific compiler
Use appropriate condition: Choose the right class condition for your validation needs
Handle NOT conditions: Use IS NOT for error checking and validation
Document expectations: Comment code to explain what format is expected
Validate early: Check class conditions as soon as data is received
Consider trimming: Trim spaces before validation if needed for your requirements

Common Mistakes with Class Conditions

Avoid these common mistakes:

Mistake 1: Assuming Spaces are Valid

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       *> WRONG: May fail if field has spaces
       IF ZIP-CODE IS NUMERIC
           *> Process ZIP code
       END-IF
       
       *> CORRECT: Trim or handle spaces
       IF FUNCTION TRIM(ZIP-CODE) IS NUMERIC
           *> Process ZIP code
       END-IF

Mistake 2: Not Validating Before Use

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       *> WRONG: No validation
       MOVE INPUT-FIELD TO NUMERIC-FIELD
       COMPUTE RESULT = NUMERIC-FIELD * 2
       
       *> CORRECT: Validate first
       IF INPUT-FIELD IS NUMERIC
           MOVE INPUT-FIELD TO NUMERIC-FIELD
           COMPUTE RESULT = NUMERIC-FIELD * 2
       ELSE
           DISPLAY "ERROR: Invalid numeric input"
       END-IF

Mistake 3: Confusing Class and Type

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       *> Class condition checks CHARACTERS, not data type
       *> A PIC X field can be numeric if it contains digits
       01  NUMERIC-STRING   PIC X(10) VALUE '12345'.
       
       *> This is TRUE even though field is PIC X
       IF NUMERIC-STRING IS NUMERIC
           DISPLAY "Field contains numeric characters"
       END-IF

Explain Like I'm 5: Class Conditions

Think of class conditions like sorting toys:

IS NUMERIC is like checking if a box contains only number blocks - if there's even one letter block, it's not all numbers
IS ALPHABETIC is like checking if a box contains only letter blocks - if there's even one number block, it's not all letters
IS ALPHANUMERIC is like checking if a box contains only letter and number blocks - if there's a special shape block, it's not alphanumeric
Validation is like checking your toy box before playing - you make sure you have the right kind of toys before you start

So class conditions are like checking what kind of characters are in your data - all numbers, all letters, or letters and numbers - before you use them!

Practice Exercises

Complete these exercises to reinforce your understanding:

Exercise 1: Numeric Validation

Create a program that accepts user input and validates it is numeric. If valid, display the number; if invalid, display an error message with the invalid input.

Exercise 2: Name Validation

Create a program that accepts a first name and last name, validates both are alphabetic, and displays appropriate error messages if validation fails.

Exercise 3: Code Validation

Create a program that accepts a product code, validates it is alphanumeric and exactly 8 characters, and processes it only if valid.

Exercise 4: Type Routing

Create a program that accepts input and routes to different processors based on whether the input is numeric, alphabetic, or alphanumeric. Use EVALUATE with class conditions.

Exercise 5: Comprehensive Validation

Create a program that validates multiple fields: a numeric account number, an alphabetic state code, and an alphanumeric customer ID. Display specific error messages for each validation failure.

Test Your Knowledge

1. What does IS NUMERIC check?

If a field contains any numbers
If all characters are digits (0-9)
If a field is a numeric data type
If a field can be converted to a number

2. What does IS ALPHABETIC check?

If a field contains any letters
If all characters are letters (A-Z, a-z)
If a field is uppercase
If a field is lowercase

3. What does IS ALPHANUMERIC check?

If a field contains letters or numbers
If all characters are letters or digits
If a field is mixed case
If a field has special characters

4. How do you check if a field is NOT numeric?

IF field NOT NUMERIC
IF field IS NOT NUMERIC
IF NOT field NUMERIC
IF field <> NUMERIC

5. What happens if a field with spaces is tested with IS NUMERIC?

Returns true
Returns false (spaces are not numeric)
Depends on the compiler
Causes an error

6. What is a primary use of class conditions?

Performance optimization
Data validation and input verification
Memory management
File operations

COBOL Tutorial

COBOL Class Conditions

What are Class Conditions?

IS NUMERIC Condition

IS NUMERIC Syntax

Example: Validating Numeric Input

Important Notes about IS NUMERIC

IS ALPHABETIC Condition

IS ALPHABETIC Syntax

Example: Validating Names

IS ALPHANUMERIC Condition

IS ALPHANUMERIC Syntax

Example: Validating Codes and IDs

Using Class Conditions in Conditional Statements

With IF Statements

With EVALUATE Statements

With Logical Operators

Data Validation Patterns

Pattern 1: Input Validation

Pattern 2: Format Validation

Pattern 3: Type-Specific Processing

Class Condition Behavior with Spaces

Best Practices for Class Conditions

Common Mistakes with Class Conditions

Mistake 1: Assuming Spaces are Valid

Mistake 2: Not Validating Before Use

Mistake 3: Confusing Class and Type

Explain Like I'm 5: Class Conditions

Practice Exercises

Exercise 1: Numeric Validation

Exercise 2: Name Validation

Exercise 3: Code Validation

Exercise 4: Type Routing

Exercise 5: Comprehensive Validation

Test Your Knowledge

Related Concepts

Related Concepts

Conditional Statements

Data Validation

Data Types

Input Processing

Related Pages