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Chapter 11

Avoiding Logic Errors by Validating Input What to Do If Input Errors Occur Global Considerations in COBOL When Data Should Be Validated Understanding Program Interrupts Other Methods for Improving Program

Performance

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Use DISPLAY statements during test runs to isolate logic errors

Include test data that produces size errors if ON SIZE ERROR routines are used

For every IF statement, use test data that satisfies and does not satisfy condition

Compile often

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Risk of data entry errors is high◦ Large volume of data entered◦ Human error keying in data

Invalid input leads to inaccurate output◦ For example, salary reported incorrectly if entered

as 23000 instead of 32000 Input error can cause program interrupt

◦ For example, spaces entered for numeric field used in arithmetic operation

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Use NUMERIC class test to ensure field used in arithmetic operation has numeric value

If Amt-In Is Not NumericPerform 500-Err-Rtn

ElseAdd Amt-In To WS-Total

End-If

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Example

Use ALPHABETIC class test if field must be alphabetic

COBOL has built in functions for the following: ◦ Values greater than zero (POSITIVE)◦ Values less than zero (NEGATIVE)◦ Value equal to zero (ZERO)

S must be included in PIC to store a negative number NOT POSITIVE is not same as NEGATIVE

◦ IF X IS POSITIVE THEN …

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Check key fields if they must contain data

If Soc-Sec-No = SpacesPerform 900-Err-Rtn

End-If

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Example

Useful for validity checking as well as other purposes

Two main functions◦ To count number of occurrences of given

character in field◦ To replace specific occurrences of given character

with another character

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To count number of times a given character occurs

INSPECT identifier-1 TALLYINGALL identifier-3

identifier-2 FOR LEADING literal-1 CHARACTERS

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Format

identifier-1◦ Field to be "inspected"

identifier-2◦ Field where count stored◦ Not automatically set to zero by INSPECT

identifier-3 or literal-1◦ Character to be counted◦ ZERO, SPACE, 8, 'S' are valid entries for literal-1

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ALL - every occurrence of specified character in field counted

LEADING - all occurrences of specified character preceding any other character tallied

CHARACTERS - all characters within field tallied◦ Used to determine size of field

Example next slide

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Move Zeros To Ct1, Ct2, Ct3Inspect X1 Tallying Ct1 For All SpacesInspect X2 Tallying Ct2 For CharactersInspect X3 Tallying Ct3 For Leading Zeros

Fields Results X1 = bb82b Ct1 = 3X2 = AB32C Ct2 = 5X3 = 00060 Ct3 = 3

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Examples

Optional clause after FOR options to count only characters before or after some initial value

BEFORE INITIAL identifier-4AFTER literal-2

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Format

Move Zeros To Ct4, Ct5Inspect X4 Tallying Ct4 For All Zeros Before Initial 9Inspect X5 Tallying Ct5 For Characters After Initial 6

Items Results X4 = 05090 Ct4 = 2X5 = 06762 Ct5 = 3

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Examples

To replace specified occurrences of a given character with another

INSPECT identifier-1 REPLACINGCHARACTERS ALL identifier-2 BY identifier-3 LEADING literal-1 literal-2 ... FIRST

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Format

Literals must be single characters or figurative constants consistent with type of field being inspected

ALL, LEADING, CHARACTERS have same meaning as previously noted

FIRST means first occurrence of literal-1 will be replaced by literal-2

BEFORE/AFTER clause can be used

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Inspect Date-In Replacing All '-' By '/'Inspect SSNo Replacing All Spaces By '-'

Field Before AfterDate-In 10-17-02 10/17/02SSNo 123 45 6789 123-45-6789

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Examples

Inspect X1 Replacing Leading 'A' By 'Z'Inspect X2 Replacing First 'R' By 'Q'

Field Before AfterX1 AAABBA ZZZBBAX2 RRSST QRSST

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Examples

Code often stored in field to shorten record and minimize typing by using the 88 numbered field

For example, 'H' or 'S' may represent pay type of 'Hourly' or 'Salaried'

Use condition names to check validity of coded fields

(covered this a few chapters ago)

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05 Pay-Code Pic X.88 Hourly Value 'H'.88 Salaried Value 'S'.

If Hourly Or Salaried ThenPerform Pay-Calc-Rtn

ElsePerform Pay-Code-Err-Rtn

End-If

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Example

Data Division entries

Procedure Division statements

Class test - determine if field contains appropriate type of data (NUMERIC, ALPHABETIC)

Determine if data is missing by comparing field to SPACES

Replace spaces in numeric fields with ZEROS using INSPECT statement

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Range test - determine if field in established range

Limit test - determine if field exceeds established limit

Determine if field contains valid codes or values using condition-names to document and test fields

Can we use the inspect to solve our data entry problem of the lack of leading zeros and decimal spaces?

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Perform class tests first to ensure field is proper type

Use EVALUATE for further validation tests Three common forms

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EVALUATE identifierWHEN value(s) PERFORM …

…

Evaluate Pay-CodeWhen 'H' Perform 300-Hourly-RtnWhen 'S' Perform 400-Salaried-Rtn

End-Evaluate

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Example

May also use THRU clause to check range of values

Evaluate AgeWhen 0 Thru 19

Perform 400-Minor-RtnWhen 20 Thru 99

Perform 500-Adult-RtnEnd-Evaluate

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Example

EVALUATE TRUEWHEN condition PERFORM …

…

Evaluate TrueWhen Age >= 0 And <= 19

Perform 400-Minor-RtnWhen Age >= 20 And <= 99

Perform 500-Adult-RtnEnd-Evaluate

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Example

Can also use with condition-names

Assume these condition names defined for Age field

05 Age Pic 99.88 Minor Values 0 Thru 19.88 Adult Values 20 Thru

99.

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Example

Evaluate TrueWhen Minor

Perform 400-Minor-RtnWhen Adult

Perform 500-Adult-RtnEnd-Evaluate

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EVALUATE conditionWHEN TRUE PERFORM …WHEN FALSE PERFORM …

Evaluate Age <= 19When True Perform 400-Minor-RtnWhen False Perform 500-Adult-Rtn

End-Evaluate

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Example

1. Print error record displaying key field, field in error and error message

2. Stop the run to preserve data integrity3. Partially process or bypass erroneous

records4. Stop the run if number of errors exceeds

predetermined limit

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5. Use switch/If or 88 field to indicate when record contains error

◦ Initialize field to 'N' for no errors◦ Set field to 'Y' anytime an error occurs◦ Process record as valid only if switch field still

'N' after all validation checks

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6. Print count totals and compare to manual counts

◦ Print count of all records processed◦ Print count of all errors encountered◦ Print batch totals or count of all records within

specific groups or batches

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Meaning of comma and decimal point in numbers in United States is reversed in some other nations

4,123.45 in United States represented as 4.123,45 in other nations

To change representation of numbers in COBOL use SPECIAL-NAMES paragraph

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** If you wanted to switch the , and . aroundEnvironment Division.Configuration Section.Special-Names.Decimal-Point is Comma.

Number 4123,45 stored in field with PIC 9999V99

When moved to report-item with PIC 9.999,99 is displayed as 4.123,45

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Data Exception◦ Performing operations on field containing

blanks or other nonnumeric characters Arithmetic operation Comparison

◦ Failing to initialize subscript or index Divide Exception - Attempting to divide by zero Addressing Error

◦ Referring to array or table entry with value in subscript or index that exceeds number of entries in table

◦ Improperly coding nested PERFORMs or exiting from paragraph being performed

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Operation Error◦ Attempting to access file with READ or WRITE

before opening it or after closing it Specification Error

◦ Attempting to access input area after AT END condition

Illegal Character in Numeric Field◦ May be caused by type mismatch between actual

data and PIC clause◦ Field size specified in PIC clause may not match

actual size of field in record, leading to invalid (nonnumeric) characters from another field being treated as part of numeric field

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Two types of program errors◦ Syntax errors◦ Logic errors

Error control procedures can minimize errors but not eliminate them entirely

Page 456 – way to input data file name from users instead of always hard-coding it.

READ…INTO Statement page 456 INITIALIZE statement

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Types of error control procedures◦ Range tests◦ Limit tests◦ Format tests◦ Tests for missing data◦ Sequence checks

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Other methods to validate data◦ INSPECT statement◦ Condition-names◦ EVALUATE verb◦ Verifying input data

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Handling input errors◦ Stop the run◦ Fill erroneous fields with spaces or zeros◦ Stop the run if number of errors excessive◦ Print control listings or audit trails to be checked

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