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Despite all the talk about reengineering business processes, it takes a long time and a lot of money to rewrite a program, especially one that works. The readability of the program will also be badly affected. But still GO TO can be used within the paragraphs being performed. It can be defined as elementary or group item. Initialization of large table occurrences with specific values are usually done using perform loops in procedure division.
Simple tables can be initialized in the following way. Dynamic array is the array whose size is decided during runtime just before the access of first element of the array. It can be used in any arithmetic operations or for display. It cannot be used for arithmetic operation or for display purpose. Subscripts can be modified by any arithmetic statement. Sometimes, you may face a question like how to randomly access the information in the sequential file of 50 records that contains all the designation and the respective lower and higher salary information.
Obviously, OS does not allow you to randomly access the sequence file. You have to do by yourself and the best way is, load the file into a working storage table in the first section of the program and then access as you wish. The table look-up can be done in two ways. If the condition is met, the table look-up is completed. If the condition is not met, then index or subscript is incremented by one and the next entry is searched and the process continues until a match is found or the table has been completely searched.
SET indexname-1 TO 1. Condition-1, Condition-2 compares an input field or search argument with a table argument.
What does a COBOL Programmer do?
Identifier-2 and identifier-3 are subscripted items and dataname-1 and dataname-2 are working storage items that are not subscripted. Compare the item to be searched with the item at the center. If it matches fine, else repeat the process with the left or right half depending on where the item lies. Table should be in sorted order of the searching argument. Only AND is possible in compound conditions.
Prefer when the table size is significantly large. Expanded nested perform is available for processing multi level tables. One program may contain other program s. The contained program s may themselves contain yet other program s. PGMB is nested a program in the example below:. If you want to manipulate the data before feeding to sort, prefer internal sort.
In all other cases, external sort is the good choice. Internal sort, in turn invokes the SORT product of your installation.
Programming in COBOL
In the run JCL, allocate at least three sort work files. It would significantly improve the performance. If the sort is successful, the value will be 0 else It should not be explicitly opened or closed. Sometimes it would be more efficient to process data before it is sorted, whereas other times it is more efficient to process after it is sorted. If we intend to eliminate more records, then it would be better preprocess them before feeding to SORT.
If we want to eliminate all the records having spaces in the key field then it would be efficient if we eliminate them after sorting. Because the records with blank key comes first after sorting. It is same as sort. USING is mandatory. A string refers to a sequence of characters. It is used to tally the occurrence of a single character or groups of characters in a data field. Main String is identifier-1 and count is stored in identifier Literal-1 or Identifier-3 is a character or group-of-characters you are looking in the main-string.
It is used to replace the occurrence of a single character or groups of characters in a data field. When it is used in array elements, the syntax is Array-element occurrence Starting-Position:Length. Common routines like error routine, date validation routine are coded in a library and bring into the program by COPY. Master files are used in multiple programs.
Their layout can be placed in one copybook and be placed wherever the files are used. It promotes program standardization since all the programs share the same layout and the same data names. This reduces coding and debugging time. Change in layout needs change in copybook only. It is enough if we just recompile the program for making the new copy effective. Copybooks can be used in the following paragraphs. If the same copybook is used more than once in the program, then there will be "duplicate data declaration" error during compilation, as all the fields are declared twice.
The replacing option does not alter the prewritten entries in the library; the changes are made to the user's source program only. When a specific functionality need to be performed in more than one program, it is best to write them separately and call them into each program. Sub Programs can be written in any programming language. They are typically written in a language best suited to the specific task required and thus provide greater flexibility.
CALL statement is used for executing the sub-program from the main program.
PGM2 is called here. WS-VAR1 is passed by reference. As we have already mentioned, the linkage section is used for accessing external elements. As these working storage items are owned by main program, to access them in the sub-program, we need to define them in the linkage section. In addition to define them in linkage section, the procedure division should be coded with these data items for address-ability. This returns the control back to main program. If the sub program is modified then it needs to be recompiled.
The need for main program recompilation is decided by the compiler option used for the main program.
The modified subroutine will be in effect during the run. Difference between Pass-by-reference and Pass-by-content. The sub-program modifications on the passed elements are visible in the main program. The sub-program modifications on the passed elements are local to that sub-program and not visible in the main program.
Difference between Static Call and Dynamic Call.
Identified by Call literal. Identified by Call variable and the variable should be populated at run time. By default, call variables and any un-resolved calls are considered as dynamic. If the subprogram undergoes change, sub program and main program need to be recompiled. If the subprogram undergoes change, recompilation of subprogram is enough. Sub modules are link edited with main module. Sub modules are picked up during run time from the load library. Program will be in initial state every time it is called. Returns the length of the PIC clause. Used for finding length of group item that spanned across multiple levels.
Returns the content of the argument that contains the maximum value. Returns the content of the argument that contains the minimum value. Returns the numeric value represented by an alphanumeric character string specified in the argument. Returns Gregorian date for the integer passed. A data file is collection of relevant records and a record is collection of relevant fields. The file is allocated to your program by this statement. The mode of OPEN decides the operation allowed and the initial pointer in the dataset.
Close: After the processing, close the file to disconnect it from the program. This can be coded only for input files. If not, an execution error will occur. The file can also be dynamically allocated instead of static allocation in JCL. Default is Sequential. It is default access mode and it is used to access the records ONLY in sequential order. To read th record, first 99 records need to be read and skipped. It is mixed access mode where the file can be accessed in random as well as sequential mode in the program. Example: Reading the details of all the employees between First randomly access th employee record, then read sequentially till th employee record.
It should be unique and part of indexed record structure. After every file operation, the file status should be checked for allowable values.
This is a 6- byte field in working storage. The number of buffers to be allocated for the file is coded here. By default two buffers will be allocated if the clause is not coded. Since similar option is available in JCL, this is not coded in program. It specifies the length of the record in terms of bytes.
It specifies the physical record size. It can be mentioned as number of logical records OR number of characters, that is multiple of logical record length. I-O time is reduced as n numbers of records are read into main memory buffer during an I-O. Inter record gap is removed and the gap exist only between blocks. So memory wastage due to IRG is avoided. If there is an OCCURS depending on clause or there are multiple 01 levels and every 01 level is of different size, then the file would be of variable length. Multiple 01 level in File section is an example for implicit redefinition.
It is used to name the data record s of the file. More than one record can be coded here. If you don't close the files, the completion of the program closes all the files used in the program. If more than one file is stored in a reel of tape, it is called as multi-file volume. When one file is stored in more than one reel of tape, it is called as multi-volume label. One reel is known as one volume. When the end of one volume is reached, automatically the next volume opens. So there is no special control is needed for multi volume files.
After opening a TAPE file, the file is positioned at its beginning. Provided hardware supports this feature When you close the file, the tape is normally rewound. This will be useful when you want skip all the records in the first reel after n number of records processing. At any point of time, you can have only one file is active in the program. READ statement is used to read the record from the file. If INTO clause is coded, then the file is directly read into working storage section record.
It is preferred as it avoids another move of file-section-record to working-storage-record followed by simple READ. Before accessing the file randomly, the key field should have a value before READ. Write statement is used to write a new record in the file. To update a record in a file, the file should be opened in I-O mode. START is used with dynamic access mode of indexed files.
START itself does not retrieve any record. To delete a record, the file should be opened in I-O mode. There are chances for failure of any file I-O processing. The failure of an I-O operation can be accepted or cannot be tolerated. The severity of failure has to be defined in the program design stage. Let us assume that we don't have any error handling in our program.
In this case, for example, if you don't have a specific record in the file, the random read of that record would immediately terminate the program with error 'record not found'. Based on the importance of the record and business rule, we can continue our program with next record or terminate the program properly.
But there is no way to handle all such errors in this way. The second method is, assigning file-status to the file in the SELECT clause and checks the file status after each and every I-O and ensures that the value of status code is one of the allowable values. If it is not an allowable return code, then abnormally end the program with error statements that would be easier to debug. But we have to do this checking after each and every I-O operation. COBOL provides an option to group all the possible errors of specific operation s in a place and that will be automatically invoked during the respective operation s of any file.
This avoids redundant code. Check the file-status code for validity. The validity of error should be checked in this paragraph and allow or restrict the process down, based on severity of error code. If file name file-1 is coded in the USE statement, then all the input-output operation of that specific file will be checked. This will be very useful when the program must work with a limited memory space.
So more than one file can be in open state. We should be careful while filling in the record area of the output file. By mid, they had increased to 11— statements per minute. This was then replaced by the COBOL Extended specifications in , which introduced the sort and report writer facilities.
They described new versions in , , and , including changes such as new inter-program communication, debugging and file merging facilities as well as improved string-handling and library inclusion features. The Programming Language Committee was not well-known, however. It was also poor, lacking the funds to make public documents, such as minutes of meetings and change proposals, freely available.
These made up 44 changes, which rendered existing statements incompatible with the new standard. The proposed standard commonly called COBOL differed significantly from the previous one, causing concerns about incompatibility and conversion costs. In January , Joseph T. Brophy described previous conversions of their million-line code base as "non-productive" and a "complete waste of our programmer resources". During the first public review period, the committee received 2, responses, of which 1, were negative form letters. Fewer than a dozen of the responses were in favor of the proposed standard.
In , the DPMA withdrew its opposition to the standard, citing the responsiveness of the committee to public concerns. In the same year, a National Bureau of Standards study concluded that the proposed standard would present few problems. The second public review drew another 1, mainly negative responses, while the last drew just 25, by which time many concerns had been addressed. It was published in late Sixty features were changed or deprecated and many [ quantify ] were added, such as:  .
The new standard was adopted by all national standard bodies, including ANSI. Two amendments followed in and , the first introducing intrinsic functions and the other providing corrections. Some vendors including Micro Focus , Fujitsu , and IBM introduced object-oriented syntax based on drafts of the full revision. The final approved ISO standard was approved and published in late NET Framework. Three corrigenda were published for the standard: two in and one in COBOL suffered from poor support: no compilers completely supported the standard. Micro Focus found that it was due to a lack of user demand for the new features and due to the abolition of the NIST test suite, which had been used to test compiler conformance.
COBOL Programming: No Punch Cards Needed - kysucihequku.ga
The standardization process was also found to be slow and under-resourced. COBOL includes the following changes: . Near the end of the 20th century, the year problem Y2K was the focus of significant COBOL programming effort, sometimes by the same programmers who had designed the systems decades before. After the clean-up effort put into these programs for Y2K, a survey found that many remained in use.
Instead, some businesses have migrated their systems from expensive mainframes to cheaper, more modern systems, while maintaining their COBOL programs. More complex conditions can be "abbreviated" by removing repeated conditions and variables. Words include reserved words and user-defined identifiers. They are up to 31 characters long and may include letters, digits, hyphens and underscores. Literals include numerals e. A COBOL program is split into four divisions: the identification division, the environment division, the data division and the procedure division. The identification division specifies the name and type of the source element and is where classes and interfaces are specified.
The environment division specifies any program features that depend on the system running it, such as files and character sets. The data division is used to declare variables and parameters. The procedure division contains the program's statements. Each division is sub-divided into sections, which are made up of paragraphs.
COBOL's syntax is usually described with a unique metalanguage using braces, brackets, bars and underlining. Although Backus—Naur form did exist at the time, the committee had not heard of it. COBOL can be written in two formats: fixed the default or free. In fixed-format, code must be aligned to fit in certain areas a hold-over from using punched cards. COBOL also introduced free-format code. Free-format code can be placed in any column of the file, as in newer programming languages. The identification division identifies the following code entity and contains the definition of a class or interface.
Classes have factory objects, containing class methods and variables, and instance objects, containing instance methods and variables. Support for generic programming is provided through parameterized classes, which can be instantiated to use any class or interface. Objects are stored as references which may be restricted to a certain type.
COBOL does not provide a way to hide methods. The environment division contains the configuration section and the input-output section. The configuration section is used to specify variable features such as currency signs, locales and character sets. The input-output section contains file-related information. COBOL supports three file formats, or organizations : sequential, indexed and relative. In sequential files, records are contiguous and must be traversed sequentially , similarly to a linked list. Indexed files have one or more indexes which allow records to be randomly accessed and which can be sorted on them.
Each record must have a unique key , but other, alternate , record keys need not be unique. Relative files, like indexed files, have a unique record key, but they do not have alternate keys. A relative record's key is its ordinal position; for example, the 10th record has a key of This means that creating a record with a key of 5 may require the creation of empty preceding records.
Relative files also allow for both sequential and random access. A common non-standard extension is the line sequential organization, used to process text files. Records in a file are terminated by a newline and may be of varying length. The data division is split into six sections which declare different items: the file section, for file records; the working-storage section, for static variables ; the local-storage section, for automatic variables ; the linkage section, for parameters and the return value; the report section and the screen section, for text-based user interfaces. Data items in COBOL are declared hierarchically through the use of level-numbers which indicate if a data item is part of another.
An item with a higher level-number is subordinate to an item with a lower one. Top-level data items, with a level-number of 1, are called records. Items that have subordinate aggregate data are called group items ; those that do not are called elementary items.
Level-numbers used to describe standard data items are between 1 and In the above example, elementary item num and group item the-date are subordinate to the record some-record , while elementary items the-year , the-month , and the-day are part of the group item the-date. Subordinate items can be disambiguated with the IN or OF keyword. For example, consider the example code above along with the following example:.
The names the-year , the-month , and the-day are ambiguous by themselves, since more than one data item is defined with those names. To specify a particular data item, for instance one of the items contained within the sale-date group, the programmer would use the-year IN sale-date or the equivalent the-year OF sale-date. This syntax is similar to the "dot notation" supported by most contemporary languages. A level-number of 66 is used to declare a re-grouping of previously defined items, irrespective of how those items are structured.
This data level, also referred to by the associated RENAMES clause , is rarely used  and, circa , was usually found in old programs. Its ability to ignore the hierarchical and logical structure data meant its use was not recommended and many installations forbade its use. A 77 level-number indicates the item is stand-alone, and in such situations is equivalent to the level-number For example, the following code declares two level data items, property-name and sales-region , which are non-group data items that are independent of not subordinate to any other data items:.
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An 88 level-number declares a condition name a so-called level which is true when its parent data item contains one of the values specified in its VALUE clause. When the data item contains a value of 'H' , the condition-name wage-is-hourly is true, whereas when it contains a value of 'S' or 'Y' , the condition-name wage-is-yearly is true. If the data item contains some other value, both of the condition-names are false.
Numeric data is converted between different representations and sizes silently and alphanumeric data can be placed in any data item that can be stored as a string, including numeric and group data. Some picture characters specify the type of the item and how many characters or digits it occupies in memory.
For example, a 9 indicates a decimal digit, and an S indicates that the item is signed. Other picture characters called insertion and editing characters specify how an item should be formatted. Repeated characters can be specified more concisely by specifying a number in parentheses after a picture character; for example, 9 7 is equivalent to Picture specifications containing only digit 9 and sign S characters define purely numeric data items, while picture specifications containing alphabetic A or alphanumeric X characters define alphanumeric data items.
The presence of other formatting characters define edited numeric or edited alphanumeric data items. While it can be used to declare pointers and object references, it is mostly geared towards specifying numeric types. These numeric formats are: . The report writer is a declarative facility for creating reports. The programmer need only specify the report layout and the data required to produce it, freeing them from having to write code to handle things like page breaks, data formatting, and headings and footings.
Reports are associated with report files, which are files which may only be written to through report writer statements. Each report is defined in the report section of the data division. A report is split into report groups which define the report's headings, footings and details.
Reports work around hierarchical control breaks. Control breaks occur when a key variable changes it value; for example, when creating a report detailing customers' orders, a control break could occur when the program reaches a different customer's orders. Here is an example report description for a report which gives a salesperson's sales and which warns of any invalid records:. For the above sales report example, the procedure division might look like this:. Use of the Report Writer facility tended to vary considerably; some organizations used it extensively and some not at all.
The sections and paragraphs in the procedure division collectively called procedures can be used as labels and as simple subroutines.
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Unlike in other divisions, paragraphs do not need to be in sections. A PERFORM statement somewhat resembles a procedure call in a modern language in the sense that execution returns to the code following the PERFORM statement at the end of the called code; however, it does not provide any mechanism for parameter passing or for returning a result value.
PERFORM also differs from conventional procedure calls in that there is, at least traditionally, no notion of a call stack. The problem arises when the code in the inner invocation reaches the exit point of the outer invocation. The reason is that COBOL, rather than a "return address", operates with what may be called a continuation address. When control flow reaches the end of any procedure, the continuation address is looked up and control is transferred to that address.
Before the program runs, the continuation address for every procedure is initialised to the start address of the procedure that comes next in the program text so that, if no PERFORM statements happen, control flows from top to bottom through the program. The original value is saved and is restored afterwards, but there is only one storage position. If two nested invocations operate on overlapping code, they may interfere which each other's management of the continuation address in several ways.
One might expect that the output of this program would be "1 2 3 4 3": After displaying "2", the second PERFORM causes "3" and "4" to be displayed, and then the first invocation continues on with "3". Therefore the behaviour in such cases is not only perhaps surprising, it is also not portable. Since there is limited space to store backup continuation addresses, the backups get overwritten in the course of recursive invocations, and all that can be restored is the jump back to DISPLAY 'END'. The report writer statements are covered in the report writer section. This can be used to implement decision tables.
For example, the following might be used to control a CNC lathe :. The PERFORM statement is used to define loops which are executed until a condition is true not while true, which is more common in other languages. It is also used to call procedures or ranges of procedures see the procedures section for more details. GO TO causes the program to jump to a specified procedure. The EXIT statement has six different formats: it can be used as a return statement, a break statement , a continue statement , an end marker or to leave a procedure.