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COBOL

COBOL . Arrays. Paragraphs. A Paragraph Name is a programmer defined name for a block of code. Must use the standard rules for programmer defined names (A-Z, 0-9, -). Must be terminated with a full-stop.

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COBOL

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  1. COBOL Arrays

  2. Paragraphs • A Paragraph Name is a programmer defined name for a block of code. • Must use the standard rules for programmer defined names (A-Z, 0-9, -). • Must be terminated with a full-stop. • Any number of statements and sentences may be included in a paragraph but the last one must be terminated with a full-stop. • The code for a Displaced Paragraph is after the STOP RUN but is called from within the main program.

  3. PERFORM • PERFORM is COBOL’s only iteration construct, and it comes in several flavours. • PERFORM … TIMES executes a block of code or a Paragraph a certain number of times. E.g. Perform 3 TIMES • PERFORM … UNTIL executes a block of code or a Paragraph until a certain condition is satisfied. • The WITH TEST BEFORE clause means that the UNTIL condition is tested before the loop body has been entered / executed. (DEFAULT) • The WITH TEST AFTER clause means that the UNTIL condition is tested after the loop body been entered / executed.

  4. PERFORM • PERFORM Print-Prime-Numbers VARYING Prime-Num FROM1 BY 1 UNTIL Prime-Num > 9999 • Out-of-Line • Performing a separate Paragraph • In-Line • Performing a chunk of code contained within the PERFORM .... END-PERFORM

  5. Single Dimensional (1-D Arrays) • Single row or column of pigeon holes or boxes used to hold pieces of information. • They provide storage of data and allow retrieval of data when required. •  To access a particular array location, you use an index value to say which pigeon hole or box you want to access.

  6. 1-D Arrays LetterBox • To deliver a letter to Apt. 15 need to walk along the row of letter boxes until they get to box number 15 before they can insert the mail into right letterbox. • To check mail, then need to walk along the row of letter boxes until get to box number 15 before can open it and check my mail. • Row of letter boxes forms a simple 1-D Array • Letter box number provides an index which can be used to locate and access data in a particular letter box. • The location (index) of my letter box is 15. • Normally each pigeon hole (box) in the Array, is called a cell.

  7. Defining arrays • Arrays (also known as Tables) provide a way of holding / manipulating multiple values for a field or a group of fields. • Providing storage for multiple pieces of the same information. • The various pieces of data are referenced by using a numeric index, so that particular entries in the array can be set, accessed, manipulated, or altered. • Array fields can be used exactly as you would any other data field in COBOL.

  8. Defining Arrays • An array is a group item, with each of its elements belonging to it • Each element has the same picture and the element occurs a number of times • Subscripting always starts at 1. • Arrays are fixed length. 01 Months-of-year. What picture? 03 Month-name pic aaa occurs 12 times. The items are month-name(1) to month-name(12)

  9. Defining Arrays • 01 <name of structure. • 02 <name of cells> occurs <no of cells> • Indexed By <name of index>

  10. Defining the index • Subscripting can be done by an independent data item or • A subscripting item can be declared with the array:- 01 Months-of-year. 03 Month-name pic aaa occurs 12 times indexed by MONTH-NO. • In this case, month-no is defined as only having a value between 1 and 12. • Month-no can be assigned a value using the SET command: Set Month-no to 1.

  11. Auto-increment loop • Equivalent to “For a:= 1 to 10 do” • The counter is given a start value, an end condition and an increment value: Perform <paragraph> varying Month-no from 1 by 1 until Month-no > 12 • Start value is 1, increment is 1, condition is Month-no > 12 • The paragraph is performed repeatedly • The condition can be tested before or after the paragraph (See “with test after” in last topic)

  12. Examples – Month Names • Often in Cobol, it is useful to convert the month number (such as 6) to the month name (such as "Jun"). • Can either do a whole series of IF tests or a 12 line EVALUATE statement. • Or we could define an array of month names and use the particular month number as an index to get the required month name from the array.

  13. Examples – Month Names • Need to define some array table fields in the WORKING-STORAGE SECTION. • Need to define a field containing the names of all 12 months • Need to create another field that references or REDEFINES this data into an array structure. • Note that we can only use the OCCURS clause on data in levels 02-49.

  14. Example – Month Names 01 W-Month-Data. 03 FILLER PIC X(36) VALUE "JanFebMarAprMayJunJulAugSepOctNovDec". 01 W-Month-Array-Table REDEFINES W-Month-Data. 03 W-Month-Array OCCURS 12 TIMES PIC X(3).

  15. 2-Dimensional Arrays • Grid or Matrix • i.e. rows and columns of boxes. Rainfall Data

  16. 2-Dimensional arrays • Each array element is a group, containing another array. 01 Box-of-chocolates. 05 Layer-of-chocolates occurs 4 times indexed by layer-no. 10 Chocolate occurs 20 times pic 99 indexed by choc-no. • An individual chocolate can be referenced as:- chocolate (layer-no, choc-no)

  17. Parallel 1-D arrays. • An array element can be a group, with individual group members being accessed separately:- 01 LAB-class. What pictures? 03 LAB-student occurs 20 times indexed by student-no. 05 Student-name pic x(20). 05 Student-machine-no pic AA99. • Student-name (1) to Student-name (20) • Student-machine-no (1) to Student-machine-no(20) • Which are the contents of • Lab-Student(1) to Lab-Student (20)

  18. Parallel 1-D Example • Suppose we have the following : • Job Codes PIC X(4) • Job Descriptions PIC X(20) • There are 1000 Job Codes and associated descriptions • How to we represent the data ? 01 W-Job-Array. 10 Job-Code-Array PIC X(4) OCCURS1000 TIMES. 10 Job-Desc-Array PIC X(20)OCCURS1000 TIMES. OR 01 W-Job-Array. 05 W-JobData OCCURS1000 TIMES. 10 Job-Code-Array PIC X(4). 10 Job-Desc-Array PIC X(20).

  19. Parallel 1-D Example Working Storage. 01 W-Count Pic 9(3). 01 W-Num-Rows Pic 9(3) value 1000. 01 W-Match-Found Pic x. MOVE "F" TO W-Match-Found PERFORM VARYING W-Count FROM 1 BY 1 UNTIL (W-Count > W-Num-Rows) OR (W-Match-Found = "T") IF Job-Code-Array (W-Count) = "X123" DISPLAY “Found “ Job-Code-Array (W-Count) “ “ Job-Desc-Array (W-Count) MOVE "T" TO W-Match-Found END-IF END-PERFORM

  20. 4 8 1 6 5 4 7 9 2 Putting values into arrays. • The value clause cannot be used with occurs • To put initial values into an array, the area needs to be redefined. • Values can be put into the redefined area • The values appear in the array 01 defined-area. 02 matrix. 03 matrix-row occurs 3 indexed by I-row. 04 matrix-element pic 9 occurs 3 indexed by I-col. 02 value-set redefines matrix pic x(9) value “481654792”.

  21. Arrays Identification Division. Program-Id. Array-handling. *Introducing 2 1-D arrays; one pre-defined *and the other to be filled. Environment Division. Configuration Section. Special-names. Currency sign is ӣ".

  22. Data Division. Data Division. Working-Storage Section. 01 Months-of-year. 03 Month-name pic aaa occurs 12 times indexed by MONTH-NO. 01 Month-names pic x(36) value "JanFebMarAprMayJunJulAugSepOctNovDec". 01 Months-expenditure. 03 Month-spending pic s9(9)v99 occurs 12 times indexed by Mon-no 01 Tot-exp pic s9(11)v99 value 0. 01 Display-y-exp pic £££,£££,£££,£££.99CR.

  23. Procedure Division Procedure Division. Move Month-names to Months-of-year. Perform varying Month-no from 1 by 1 until Month-no > 12 Display Month-name (month-no), ":" with no advancing Set Mon-no to Month-no Accept Month-spending (Mon-no) Add Month-spending (Mon-no) to Tot-exp End-Perform Move Tot-exp to Display-y-exp Display " ". Display "Total yearly expenditure is “ Display-y-exp. Stop run.

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