1. PowerPoint Presentation: Richard H. Baum, Ph.D. DeVry Institute of Technology 9th Edition Structured COBOL Programming Nancy Stern Hofstra University Robert A. Stern Nassau Community College “Copyright @ 2000 John Wiley & Sons, In. All rights reserved. Reproduction or translation of this work beyond that permitted in Section 117 of the 1976 United States Copyright Act without the express permission of the copyright owner is unlawful. Request for further information should be addressed to the permissions Department, John Wily & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages, caused by the use of these programs or from the use of the information contained herein.”

2. Structured COBOL Programming, Stern & Stern, 9th Edition CHAPTER 12 Array Processing and Table Handling

3. Structured COBOL Programming, Stern & Stern, 9th Edition OBJECTIVES To familiarize you with: 1. How to establish a series of items using an OCCURS clause. 2. How to access and manipulate data stored in an array or table. 3. The rules for using an OCCURS clause in the DATA DIVISION. 4. The use of a SEARCH or SEARCH ALL for a table look- up.

4. Structured COBOL Programming, Stern & Stern, 9th Edition CONTENTS An Introduction to Single-Level OCCURS Clauses –Why OCCURS Clauses Are Used –Rules for Use of the OCCURS Clause Processing Data Stored in an Array –Using OCCURS with VALUE and REDEFINES Clauses –Printing Data Stored in an Array

5. Structured COBOL Programming, Stern & Stern, 9th Edition CONTENTS Using an OCCURS Clause for Table Handling –Defining a Table –Storing the Table in WORKING-STORAGE –Looking Up Data in a Table: Finding a Match Use of the SEARCH Statement for Table and Array Processing –Format of the SEARCH Statement –The INDEXED BY Clause and the SEARCH Statement –Modifying the Contents of an Index

6. Structured COBOL Programming, Stern & Stern, 9th Edition CONTENTS –Using Two WHEN Clauses for an Early Exit from a SEARCH –Searching for Multiple Matches –Internal vs... External Tables Looking up Table Data for Accumulating Totals The SEARCH... VARYING Option for Processing Parallel Tables

7. Structured COBOL Programming, Stern & Stern, 9th Edition CONTENTS The SEARCH ALL Statement –Definition of a Serial Search –Definition of a Binary Search –Format of the SEARCH ALL Statement –ASCENDING or DESCENDING KEY with the SEARCH ALL Statement

8. Structured COBOL Programming, Stern & Stern, 9th Edition CONTENTS Multiple-Level OCCURS Clause –Accessing a Double-Level or Two-Dimensional Array –Defining a Double-Level or Two-Dimensional Array –Using PERFORM... VARYING... AFTER –Using a Double-Level or Two-Dimensional Array for Accumulating Totals –Performing a Look-Up Using a Double-Level OCCURS

9. Structured COBOL Programming, Stern & Stern, 9th Edition An Introduction to Single-Level OCCURS Clauses

10. Structured COBOL Programming, Stern & Stern, 9th Edition Why OCCURS Clauses Are Used SOME USES OF OCCURS 1. Defining a series of input or output fields, each with the same format. 2. Defining a series of totals in WORKING- STORAGE to which amounts are added; after all data is accumulated. 3. Defining a table in WORKING-STORAGE to be accessed by each input record. With a table, we use the contents of some input filed to "look up" the required data in the table.

11. Structured COBOL Programming, Stern & Stern, 9th Edition Defining Fields with an Occurs Clause With an occurs clause, we specify the number of items being defined in the array and the PIC clause of each as follows: 01 TEMP-REC. 05 TEMPERATURE OCCURS 24 TIMES PIC X9(3) This OCCURS clause defines 24 three- position numeric fields. –Thus, TEMPERATURE is an array that refers to 72 positions or bytes of storage.

12. Structured COBOL Programming, Stern & Stern, 9th Edition Defining a Subscript Collectively, these 24 fields within the array are called TEMPERATURE, which is the identifier used to access them in the the PROCEDURE DIVISION. We use the identifier TEMPERATURE along with a subscript that indicates which of the 24 fields we wish to access: DISPLAY TEMPERATURE (23)

13. Structured COBOL Programming, Stern & Stern, 9th Edition SUMMARY OF OCCURS AND SUBSCRIPTS 1. An OCCURS clause is defined in the DATA DIVISION to indicate the repeated occurrence of items in an array that have the same format. 2. A subscript is used in the PROCEDURE DIVISION to indicate which specific item within the array we wish to access.

14. Structured COBOL Programming, Stern & Stern, 9th Edition QUESTIONS?

15. Structured COBOL Programming, Stern & Stern, 9th Edition SELF-TEST Consider the following for Questions 1 through 5: 01 IN-REC. 05 AMT1 PIC 9(5). 05 AMT2 PIC 9(5). 05 AMT3 PIC 9(5). 05 AMT4 PIC 9(5). 05 AMT5 PIC 9(5).

16. Structured COBOL Programming, Stern & Stern, 9th Edition SELF-TEST 1. An OCCURS clause could be used in place of defining each AMT field separately because ____. SOLUTION: all AMTs have the same format or PIC clause

17. Structured COBOL Programming, Stern & Stern, 9th Edition SELF-TEST 2. (T or F) Suppose AMT2 and AMT4 had PIC 9(3). An OCCURS clause could not be used to define all the AMT fields. SOLUTION: T

18. Structured COBOL Programming, Stern & Stern, 9th Edition SELF-TEST 3. Recode the fields within IN-REC using an OCCURS clause. SOLUTION: 01 IN-REC. 05 AMT OCCURS 5 TIMES PIC 9(5).

19. Structured COBOL Programming, Stern & Stern, 9th Edition SELF-TEST 4. To access any of the five items defined with the OCCURS clause, we must use a ____ in the PROCEDURE DIVISION. SOLUTION: subscript

20. Structured COBOL Programming, Stern & Stern, 9th Edition SELF-TEST 5. Code a routine to determine the total of all five AMT fields. Assume that a field called SUB has been defined in WORKING- STORAGE to serve as a subscript. SOLUTION: COBOL 85 (With an In-line PERFORM) MOVE ZEROS TO TOTAL PERFORM VARYING SUB FROM 1 BY 1 UNTIL SUB > 5 ADD AMT (SUB) TO TOTAL END-PERFORM...

21. Structured COBOL Programming, Stern & Stern, 9th Edition Using an OCCURS in WORKING- STORAGE for Storing Totals We have seen that an OCCURS clause may be used as part of an input record to indicate the repeated occurrence of incoming fields. Similarly, an OCCURS may be used as part of an output record to define a series of fields. An OCCURS clause may be used to define fields either in the FILE SECTION or in WORKING-STORAGE.

22. Structured COBOL Programming, Stern & Stern, 9th Edition Rules for Use of the OCCURS Clause Levels 02--49 –An OCCURS clause may be used on levels 02-- 49 only. –That is, the OCCURS is not valid for the 01 level since it must be used for defining fields, not records. Elementary or Group Items may also be defined with an OCCURS Clause.

23. Structured COBOL Programming, Stern & Stern, 9th Edition Processing Data Stored in an Array

24. Structured COBOL Programming, Stern & Stern, 9th Edition Using OCCURS with VALUE and REDEFINES Clauses Sometimes we want to initialize elements in a table or an array with specific values. We have seen that with COBOL 85 you can use a VALUE clause to set an entire array to zero: 01 ARRAY-1 VALUE ZERO. 05 TOTALS OCCURS 50 TIMES PIC 9(5).

25. Structured COBOL Programming, Stern & Stern, 9th Edition Using an OCCURS Clause for Table Handling

26. Structured COBOL Programming, Stern & Stern, 9th Edition Defining a Table A table is a list of stored fields that are looked up or referenced by the program. Tables are used in conjunction with table look-ups, where a table look-up is a procedure that finds a specific entry in the table. Thus, an array stores data or totals to be outputted, whereas a table is used for looking up or referencing data.

27. Structured COBOL Programming, Stern & Stern, 9th Edition Storing the Table in WORKING-STORAGE Storing data in a table file rather than in each transaction record is more efficient because it minimizes data entry operations. –It is also more efficient because the data can be more easily maintained, or updated, in a separate table, as needed. Any time input records need to be saved for future processing, use a READ…INTO to store the data in WORKING-STORAGE.

28. Structured COBOL Programming, Stern & Stern, 9th Edition Use of the SEARCH Statement for Table and Array Processing

29. Structured COBOL Programming, Stern & Stern, 9th Edition Format of the SEARCH Statement SEARCH identifier-1 [AT END imperative-statement-1] WHEN condition-1{imperative- statement-2} {NEXT SENTENCE}... [END-SEARCH]* *COBOL 85 only. If END-SEARCH is used, NEXT SENTENCE must be replaced with CONTINUE unless your COBOL 85 compiler has an enhancement that permits it.

30. Structured COBOL Programming, Stern & Stern, 9th Edition Using the SEARCH... AT END for Data Validation With the SEARCH statement, the AT END clause specifies what should be done if the table has been completely searched and no match is found. Since it is possible for input errors to occur, we strongly recommend that you always use this optional clause. –Without it, the ``no match'' condition would simply cause the program to continue with the next sentence; thus producing incorrect results or even a program interrupt.

31. Structured COBOL Programming, Stern & Stern, 9th Edition The INDEXED BY Clause and the SEARCH Statement When using a SEARCH statement, table entries must be specified with an index rather than a subscript. An index is similar to a subscript, but it is defined along with the table entries as part of the OCCURS description: 01 SALES-TAX-TABLE. 05 TABLE-ENTRIES OCCURS 1000 TIMES INDEXED BY X1. 10 WS-ZIPCODE PIC 9(5). 10 WS-TAX-RATE PIC V999.

32. Structured COBOL Programming, Stern & Stern, 9th Edition How an Index Differs From a Subscript Indexes are processed differently and more efficiently than subscripts. When you define an index, the computer sets up an internal storage area called an index register. Registers use the displacement values determined by the index to access table addresses. –This is faster than working with subscripts. –We recommend that you use indexes and SEARCH statements for table look-ups.

33. Structured COBOL Programming, Stern & Stern, 9th Edition How an Index Differs From a Subscript Because an index refers to a displacement and not just an occurrence value, its contents cannot be modified with a MOVE, ADD, or SUBTRACT like a subscript can. To change the contents of an index, then, we use either: (1) a PERFORM... VARYING, which can vary the values in either subscripts or indexes. (2) a SET statement, which can move, add, or subtract values in an index.

34. Structured COBOL Programming, Stern & Stern, 9th Edition Modifying the Contents of an Index: The SET Statement Basic Format: SET index-name-1 {TO} {UP BY} {DOWN BY} integer-1 EXAMPLES: Statement Meaning 1. SET X1 TO 1 Move 1 to the X1 index. 2. SET X1 UP BY 1 Add 1 to the X1 index. 3. SET X1 DOWN BY 1 Subtract 1 from the X1 index.

35. Structured COBOL Programming, Stern & Stern, 9th Edition Initializing an Index Before Using the SEARCH A SEARCH statement does not automatically initialize the index at 1 because sometimes we may want to begin searching a table at some point other than the beginning. Initializing an index at 1 must be performed by a SET statement prior to the SEARCH if we want to begin each table look-up with the first entry; for example: SET X1 TO 1

36. Structured COBOL Programming, Stern & Stern, 9th Edition DIFFERENCES BETWEEN SUBSCRIPTS AND INDEXES Subscript represents an occurrence of an array or table element. –Defined in a separate WORKING-STORAGE entry. To change a subscript's value, use a PERFORM... VARYING or any of the following: MOVE 1 TO SUB ADD 1 TO SUB SUBTRACT 1 FROM SUB

37. Structured COBOL Programming, Stern & Stern, 9th Edition DIFFERENCES BETWEEN SUBSCRIPTS AND INDEXES Index represents a displacement from the first address in the array or table. –Defined along with the OCCURS for the array or table To change an index value, use a PERFORM... VARYING or any of the following: SET X1 TO 1 SET X1 UP BY 1 SET X1 DOWN BY 1

38. Structured COBOL Programming, Stern & Stern, 9th Edition THE SEARCH... VARYING OPTION FOR PROCESSING PARALLEL TABLES Format: SEARCH identifier-1 VARYING {identifier-2} {index-name-1} [AT END imperative-statement-1] {WHEN condition-1 {imperative- statement-2}{NEXT SENTENCE} [END-SEARCH]* *COBOL 85 only. The NEXT SENTENCE clause is not permitted with the END-SEARCH unless your compiler has an enhancement that allows it.

39. Structured COBOL Programming, Stern & Stern, 9th Edition The SEARCH ALL Statement

40. Structured COBOL Programming, Stern & Stern, 9th Edition Definition of a Serial Search 1. The first entry in the table is searched. 2. If the condition is met, the table look-up is completed. 3. If the condition is not met, the index or subscript is incremented by one, and the next entry is searched. 4. This procedure is continued until a match is found or the table has been completely searched.

41. Structured COBOL Programming, Stern & Stern, 9th Edition Definition of a Serial Search A sequential or serial search, as described here, is best used when either: 1. The entries in a table are not in either ascending or descending sequence; that is, they are arranged randomly; or, 2. Table entries are organized so that the first values are the ones encountered most frequently; in this way, access time is minimized because you are apt to end the search after the first few comparisons.

42. Structured COBOL Programming, Stern & Stern, 9th Edition Definition of a Binary Search When table entries are arranged in sequence by some field, such as T- CUSTOMER-NO, the most efficient type of look-up is a binary search. The following is the way the computer performs a binary search:

43. Structured COBOL Programming, Stern & Stern, 9th Edition Definition of a Binary Search 1. Begin by comparing CUST-NO of the input customer record to the middle table argument for T-CUSTOMER-NO. –For example, this might be the twenty-fifth entry in the table. 2. Since T-CUSTOMER-NOs are in sequence, if CUST-NO-IN > T- CUSTOMER-NO (25) - which is the middle entry in our table - this eliminates the need for searching the first half of the table. –In such a case, we compare CUST-NO-IN to T- CUSTOMER-NO (37), the middle table argument of the second half of the table (rounding down), and continue our comparison in this way.

44. Structured COBOL Programming, Stern & Stern, 9th Edition Definition of a Binary Search 3. If CUST-NO-IN < T-CUSTOMER-NO (25), we compare CUST-NO-IN to T-CUSTOMER-NO (12); –that is, we divide the top half of the table into two segments and continue our comparison. 4. The binary search is complete either (a) when a match has been found, that is, CUST-NO-IN = T-CUSTOMER-NO (X1), or (b) when the table has been completely searched.

45. Structured COBOL Programming, Stern & Stern, 9th Edition Uses of a Binary Search 1. When table entries are arranged in some sequence - either ascending or descending. 2. When tables with a large number of sequential entries (e.g., 50 or more) are to be looked up or searched. For small tables or those in which entries are not arranged in a sequence, the standard serial search look-up method previously described is used.

46. Structured COBOL Programming, Stern & Stern, 9th Edition Format for SEARCH ALL SEARCH ALL identifier-1 [AT END imperative-statement-1] WHEN {data-name-1 { IS EQUAL TO} {IS =} {identifier-2} {literal-1} {arithmetic-expression-1}} {condition-name-1 [AND {data-name-2 {IS EQUAL TO} {IS =} {identifier-3}{literal-2}{arithmetic-expression-2}}] {condition-name-2}... {imperative-statement-2} {NEXT SENTENCE} [END-SEARCH]* Cobol 85 only. NEXT SENTENCE cannot typically be used with END-SEARCH.

47. Structured COBOL Programming, Stern & Stern, 9th Edition Limitations of the SEARCH ALL Statement 1. The condition following the word WHEN can test only for equality: Valid: WHEN T-CUSTOMER-NO (X1) = CUST-NO-IN Invalid: WHEN T-WEIGHT-MAX (X1) < WEIGHT-MAILED

48. Structured COBOL Programming, Stern & Stern, 9th Edition Limitations of the SEARCH ALL Statement 2. If the condition following the word WHEN is a compound conditional: a. Each part of the conditional can only consist of a relational test that involves an equal condition. b. The only compound condition permitted is with ANDs, not ORs. –Valid: WHEN S-AMT (X1) = AMT1 AND TAX- AMT (X1) = AMT2 –Invalid: WHEN SALES-AMT (X1) = AMT3 OR AMT4 = AMT5

49. Structured COBOL Programming, Stern & Stern, 9th Edition Limitations of the SEARCH ALL Statement 3. Only one WHEN clause can be used with a SEARCH ALL. 4. The VARYING option may not be used with the SEARCH ALL. 5. The OCCURS item and its index, which define the table argument, must appear to the left of the equal sign. Valid: WHEN S-AMT (X1) = AMT1... Invalid: WHEN AMT1 = S-AMT (X1)...

50. Structured COBOL Programming, Stern & Stern, 9th Edition ASCENDING or DESCENDING KEY with the SEARCH ALL Statement 1. To use the SEARCH ALL statement, we must indicate which table entry will serve as the key field. 2. That is, we specify the table entry that will be in sequence so that the binary search can be used to compare against that field. 3. We must indicate whether that KEY is ASCENDING or DESCENDING.

51. Structured COBOL Programming, Stern & Stern, 9th Edition ASCENDING or DESCENDING KEY with the SEARCH ALL Statement ASCENDING KEY - Entries are in sequence and increasing in value. DESCENDING KEY - Entries are in sequence and decreasing in value. Format: (level-number 02--49) identifier-1 OCCURS integer-1 TIMES {ASCENDING} {DESCENDING} KEY IS data-name-2 INDEXED BY index-name-1

52. Structured COBOL Programming, Stern & Stern, 9th Edition Differences Between the SEARCH and the SEARCH ALL SEARCH –Performs a serial search –Table entries need not be in any sequence –Requires a SET statement prior to the SEARCH to specify the starting point for the look-up –Can include any relational test with the WHEN clause (, =, =) or any compound conditional –May include multiple WHEN clauses

53. Structured COBOL Programming, Stern & Stern, 9th Edition Differences Between the SEARCH and the SEARCH ALL SEARCH ALL –Performs a binary search –Tables entries must be in sequence by the table argument or even the table function. The field that is in sequence is specified in an ASCENDING or DESCENDING KEY clause as part of the OCCURS entry –Does not need a SET prior to the SEARCH ALL –Can only have a single = condition tested with the WHEN clause –May only have one WHEN clause

54. Structured COBOL Programming, Stern & Stern, 9th Edition MULTIPLE-LEVEL OCCURS CLAUSE When describing an area of storage, more than one level of OCCURS may be used. As many as seven levels of OCCURS are permitted with COBOL 85, and as many as three levels are permitted with COBOL 74. Like a single-level OCCURS, multiple levels of OCCURS may be used for: (1) accumulating totals in an array. (2) storing a table for ``look-up'' purposes.

55. Structured COBOL Programming, Stern & Stern, 9th Edition RULES FOR USING A DOUBLE- LEVEL OCCURS 1. If an item is defined by a double-level OCCURS clause, it must be accessed by two subscripts. 2. The first subscript refers to the higher- level OCCURS; the second subscript refers to the lower-level OCCURS. 3. The subscripts must be enclosed in parentheses.

56. Structured COBOL Programming, Stern & Stern, 9th Edition RULES FOR USING A DOUBLE- LEVEL OCCURS 4. Subscripts may consist of positive integers or data-names with positive integer contents. 5. On most systems, the left parenthesis must be preceded by at least one space; similarly, the right parenthesis must be followed by a period, if it is the end of a sentence, or at least one space. – The first subscript within parentheses is followed by a comma and a space.

57. Structured COBOL Programming, Stern & Stern, 9th Edition Expanded Format for Accessing a Double-Level or Two-Dimensional Array PERFORM [procedure-name-1 [{THROUGH} {THRU} procedure-name-2] [WITH TEST {BEFORE} {AFTER}] VARYING {identifier-2} {index-name-1} FROM {identifier-3}{index-name-2} {literal-1} BY {identifier-4} {literal-2} UNTIL condition-1 [AFTER{identifier-5}{index-name-3} FROM {identifier-6}{index-name-4} {literal-3} BY {identifier-7} {literal-4} UNTIL condition-2] [END-PERFORM]*

58. Structured COBOL Programming, Stern & Stern, 9th Edition THE NET:Stern COBOL Web Site To access the Stern COBOL home page, go to: http://www.wiley.com/cobol/ One of the supplements includes more information on multiple-level arrays that you may download

59. Structured COBOL Programming, Stern & Stern, 9th Edition CHAPTER SLIDES END HERE CHAPTER SUMMARY COMES NEXT

60. Structured COBOL Programming, Stern & Stern, 9th Edition CHAPTER SUMMARY A. OCCURS clauses are used in the DATA DIVISION to specify the repeated occurrence of items with the same format. 1. OCCURS clauses may be written on levels 02- -49. 2. An OCCURS clause may specify an elementary or group item. B. Use an OCCURS clause to define arrays and tables. 1. Array: An area used for storing data or totals. 2. Table: A set of fields used in a table look-up.

61. Structured COBOL Programming, Stern & Stern, 9th Edition CHAPTER SUMMARY C. Use of the SEARCH statement for table handling: 1. The identifier used with the SEARCH verb is the one specified on the OCCURS level. 2. The AT END clause specifies what is to be done if the table has been searched and the required condition has not been met. 3. The WHEN clause indicates what to do when the condition is met.

62. Structured COBOL Programming, Stern & Stern, 9th Edition CHAPTER SUMMARY 4. When using a SEARCH statement, table entries are specified with the use of an index, rather than a subscript. a. The index is defined along with the OCCURS. For example: 01 UNIT-PRICE-TABLE. 05 STORED-ENTRIES OCCURS 500 TIMES INDEXED BY X1. b. An index cannot be modified with a MOVE, ADD, or SUBTRACT statement. Use a SET statement when altering the contents of an index, or use the PERFORM... VARYING. c. SET the index to 1 before using a SEARCH. d. Use a PERFORM... VARYING to load the table.

63. Structured COBOL Programming, Stern & Stern, 9th Edition CHAPTER SUMMARY D. The SEARCH ALL statement - uses and limitations. 1. Used to perform a binary search. 2. Can test only an equal condition. 3. If using a compound condition: (a) each part can only test an equal condition and (b) only ANDs are permitted. 4. Only one WHEN clause can be used. 5. The ASCENDING or DESCENDING KEY is specified along with the OCCURS and INDEXED BY clauses of a table entry.

64. Structured COBOL Programming, Stern & Stern, 9th Edition CHAPTER SUMMARY E. Multiple-level OCCURS 1. May be used for an array or a table. 2. The lowest-level OCCURS data-name or an item subordinate to it is used to access an entry in the array or the table. 3. If we use a SEARCH for accessing a multiple- level table, INDEXED BY must be used on all OCCURS levels. 4. The identifier used with the SEARCH statement should typically be the one on the lowest OCCURS level. Only the index on the same level as the OCCURS level will be incremented by the SEARCH.

65. Structured COBOL Programming, Stern & Stern, 9th Edition CHAPTER SUMMARY F. COBOL 85 permits seven levels of OCCURS; COBOL 74 permits three levels.