COBOL Reference Page

COBOL Reference Page
Programming Languages, Gordon College, Spring 2003

Program Organization

A COBOL program is coded in four divisions: IDENTIFICATION DIVISION. ENVIRONMENT DIVISION. DATA DIVSION. PROCEDURE DIVISION. within each division we find one or more sections. For example, the DATA DIVISION normally has a FILE SECTION and a WORKING-STORAGE SECTION. This subdivision continues: Program Division Sections One or more paragraphs One of more sentences. <-- terminated by period Statement (verb) Clause (modifiers) Words Characters The individual divisions will be described in more detail below.

Character set

The actual character set available to a COBOL programmer depends upon the implementation used; however, all versions of COBOL support the following characters, blank .<(+$*);-/,>=" ABCDEFGHIJKLMNOPQRSTUVWXYZ 0123456789

Identifiers

COBOL identifers are 1-30 alphanumeric characters, at least one of which must be non-numeric. In certain contexts it is permissible to use a totally numeric identifier; however, that usage is discouraged. Hyphens may be included in an identifier anywhere except the first of last character.

Reserved words

Our version of COBOL has more than 500 of reserved words which cannot be used for other purposes in a program. Click here for a list of all reserved words in Compaq COBOL. Reserved words may not be used for any purpose other than that proscribed by the language definition.

Data types and Variables

COBOL supports variables which are either alphabetic, numeric, or alphanumeric. Variable declaration Variables must be declared in a COBOL program prior to their use. Declarations occur in the DATA DIVISION. Data items are either "elementary data items" or "record description entries." Elementary items An elementary data item is a variable which contains a single value. For example, one might define a variable HOURS-WORKED to be an integer with up to 2 digits as follows: DATA DIVISION. WORKING-STORAGE SECTION. 77 HOURS-WORKED PICTURE 99 IS ZERO. The 77 above is referred to as a level number. Level 77 is specific level number used to describe elementary items in the working storage section of the data division. Note that this data item also has included an optional initialization value. Values may be either literal or figurative. Literal values are written as follows. Numeric 1-18 digits Option: may be preceeded by + or - sign Option: may include an embedded decimal point Alphabetic 0 or more characters enclosed in quotes ("). Option: to include a quote in a literal string, type two quotes. Figurative values are: ZERO ZEROES ZEROS SPACE SPACES ALL "string" the ALL modifier is used to fill an alphabetic variable with copies of the string. For example, 77 OUTPUT-STRING PICTURE X(21) IS ALL "+-". would be the same as 77 OUTPUT-STRING PICTURE X(21) IS "+-+-+-+-+-+-+-+-+-+-+". Group items A record is a group of items which contain related data values. For example, we might define a record as follows: DATA DIVISION. WORKING-STORAGE SECTION. 01 ALBUM. 05 TITLE PICTURE X(30). 05 GENRE PICTURE X(10). 05 ARTIST. 10 FIRST-NAME PICTURE X(20). 10 LAST-NAME PICTURE X(20). 10 BAND-NAME PICTURE X(20). 05 ID-NUMBER PICTURE X(10). 05 YEAR PICTURE 9999. The level numbers above are used to show subordination of groups of values. Level 01 is the uppermost level in the hierarchy. Other numbers can be chosen as the programmers preference in the range of 02-49. All items with the same level number are at the same hierarchical level in the record, referenced through the data name that subordinates them. In other words, this data description shows a group called ALBUM with the five subordinate items, TITLE, GENRE, ID-NUMBER and YEAR (all elementary) and another group called ARTIST with three elementary items, FIRST-NAME, LAST-NAME, and BAND-NAME. Note: all user-defined names at the 01-level must be unique; however, it is permissible to use the same subordinate names in other group variables. Group items can be referenced in a program as an entire unit, for example, ALBUM or by the items within the structure. For example, we may have, TITLE OF ALBUM or BAND-NAME OF ARTIST OF ALBUM to refer to specific data items. Boolean data items COBOL does not directly support logical/boolean variables; however, level-88 is used to define condition names which have the same effect. For example, suppose we have a variable called CLASS-YEAR which is a number in the range 0-5 with the following interpretation: 0 a student who has been accepted but has not yet registered for courses 1 a student in the freshman year 2 sophomore 3 junior 4 senior 5 graduate 77 CLASS-YEAR PIC 9. 88 NON-MATRICULATED VALUE 0. 88 FROSH VALUE 1. 88 SOPH VALUE 2. 88 JUNIOR VALUE 3. 88 SENIOR VALUE 4. 88 GRADUATE VALUE 5. 88 INVALID-CLASS VALUES 6,7,8,9. which would allow statements like IF GRADUATE ... whose result would be determined by the value currently stored in CLASS-YEAR when this statement is processed. Note that it is possible to have more than one value associated with a condition. For example, above, if any number outside 0 through 5 is stored in CLASS-YEAR the data name INVALID-CLASS will become true. PICTURE clause All elementary items havea PICTURE which defines the type of data which can be stored in the variable. PICTURE clauses are built from PICTURE characters whose function is shown below.

Numeric items

9    a single numeric digit
V    the virtual decimal point 
S    the number will be signed; note: if omitted the
     value is interpreted as positive regardless of
     the sign included
P    special topic


Alphabetic/Alphanumeric items

A    a character in the range "A" to "Z"
9    a single numeric digit interpreted as a character
X    any character:  A | 9

Numeric edited (output only)

9    same as above for numeric items
V    ditto
S    ditto
P    ditto
Z    if data in this position and all to the left are
     0, then print blank
B    a single blank
/    a single slash (useful in dates)
$    a single "$" prints as it stands, but this can 
     also "float"  for example,
     
         $$$$$99.99
         
     would print the "$" to the left of the most significant
     digit, preceeded by as many blanks as needed to fill
     the picture
*    Floating character but all columns to the left of the
     most significant digit will print with "*"
,    Insert a comma, suppresses if all leading characters
     are spaces, for example,
     
         Z,ZZZ,ZZ9.99
     
.    actual decimal point (corresponds to the virtual
     decimal point but it actually prints)
-    forces printing of space (for positive) or "-" (for
     negative).  Can be placed at either end of the
     clause.  Can float like "$".
+    forces printing of "+" (for positive) or "-" (for
     negative).  Can be placed at either end of the
     clause.  Can float like "$".
CR   print two spaces for positive or "CR" for negative
     number.  Can be used only at end of number.
DB   print two spaces for positive or "DB" for negative
     number.  Can be used only at end of number.
0    special topic related to P above.


Alphanumeric edited

9    Same as numeric edited
A    ditto
X    ditto
0    ditto
B    ditto
/    ditto

Note that data for a numeric item can only contain digits. The actual value in the data stream will not contain decimal point (the virtual decimal point implies its position) or a sign character. If the number is positive, this is not a problem; however, when entering a negative numeric datum one most use a very cryptic method. The original implementations of COBOL required a multipunched card where the last digit was overstruck with the punch for a "-" sign. Since we can't multipunch on the keyboard, we instead must replace the last digit of a negative number with a different symbol indicating the sign. On our implementation this is done as follows:

Actual last digit      Symbol entered

         0                   }
         1                   J
         2                   K
         3                   L
         4                   M
         5                   N
         6                   O  <-- letter "O"
         7                   P
         8                   Q
         9                   R

So to enter the value -2345 one would enter 234N into the input stream. The following summary is very useful.

Class	Data values may contain	Picture clause characters
Numeric	Only digits	9 V S P
Alphabetic	Only letters and spaces	A
Alphanumeric	Any characters	9 A X
Numeric edited	Digits and editing characters	+ $ Z 9 . CR - * B ) , / DB
Alphanumeric edited	Any COBOL character and editing characters B and 0	9 A X B 0 /
Reference: COBOL for Students: A Programming Primer, Robert G Finkenaur, Winthrop Publishers, Cambridge, MA, 1977, page 136

Assignment Statements

The MOVE verb is used for assignment in COBOL. It can be used in many ways, all of which follow the pattern, MOVE source TO destination for example, 77 FIRST-DATUM PIC 999. 77 SECOND-DATUM PIC 999. * IN PROCEDURE DIVISION MOVE 123 to FIRST-DATUM. MOVE ZERO TO SECOND-DATUM. MOVE ZERO TO FIRST-DATUM, SECOND-DATUM. MOVE FIRST-DATUM TO SECOND-DATUM. All of the above are valid syntax for the MOVE verb. An alternate form called MOVE CORRESPONDING is very useful when moving items from one group variable to another. For example, 01 ALBUM. 05 TITLE PIC X(30). 05 GENRE PIC X(10). 05 ARTIST. 10 FIRST-NAME PIC X(20). 10 LAST-NAME PIC X(20). 10 BAND-NAME PIC X(20). 05 ID-NUMBER PIC X(10). 05 YEAR PIC 9999. 01 MUSIC-VIDEO. 05 ARTIST. 10 FIRST-NAME PICTURE X(20). 10 LAST-NAME PICTURE X(20). 10 BAND-NAME PICTURE X(20). 05 FIRST-BROADCAST. 10 MONTH PIC 99. 10 DAY PIC 99. 10 YEAR PIC 999. * IN PROCEDURE DIVISION MOVE CORRESPONDING MUSIC-VIDEO TO ALBUM. This would result in the FIRST-NAME, LAST-NAME and BAND-NAME of MUSIC-VIDEO all being copied into the fields of the same name in ALBUM. IMPORTANT - the size of the destination field must be large enough to accomodate the data which will be copied or truncation errors will result. Truncation will occur at either end of a number. For example,

source value      destination's PIC clause      destination value
 (numeric)           (numeric edited)
 
  013_^52               9999.999                     0013.520
  252_^35                999.99                       252.35
  252_^35                 99.99                        52.35
  252_^35                 99.9                         52.3

Note that the data are lined up with respect to the virtual decimal point. When needed zeroes may be padded onto either end of the value or actual digits will be truncated. For alphabetic and alphanumeric items, the fields are left justified padded with spaces or truncated from the right. Assignment through computed results Unlike most procedural languages, COBOL does not use the form <variable> := <expression> to store results of a computation. Rather, the computation VERBS are used to give this functionality. For example, some of the forms allowed include, ADD item TO resultItem ADD item TO resultItem1, resultItem2, ... ADD item1 TO item2 GIVING result ADD item1, item2, ... GIVING result SUBTRACT item FROM resultItem SUBTRACT item FROM resultItem1, resultItem2, ... SUBTRACT item1 FROM item2 GIVING result SUBTRACT item1, item2, ... GIVING result MULTIPLY item BY resultItem MULTIPLY item BY resultItem1, resultItem2, ... MULTIPLY item1 BY item2 GIVING result DIVIDE denominator INTO resultNumerator DIVIDE denominator INTO resultNumerator1, resultNumerator2, ... DIVIDE denominator INTO numerator GIVING result DIVIDE numerator BY denominator GIVING result DIVIDE numerator BY denominator GIVING result REMAINDER remainderItem All of these forms can include the option ROUNDED, as in, DIVIDE denominator INTO resultNumerator ROUNDED as well as the optional clause, ON SIZE ERROR, such as, MULTIPLY item1 BY item2 GIVING result ROUNDED ON SIZE ERROR imperative-statement which can be used to trap results that overflow the PICTURE of the resulting variable. Otherwise, truncations simply occur. Note, also, division with the GIVING clause also allows the optional REMAINDER clause. Note that the remainder will be affected by the PICTURE of the quotient item as well as the remainder item.

Control Statements

COBOL programs begin execution with the first sentence of the first paragraph and continue in sequence until one of the following occurs: the last sentence of the last paragraph is executed, an explicit program termination statement is executed, or a control structure causes execution to continue in another place in the program. COBOL supports the standard control structures: subroutine call, selection, and repetition. COBOL supports nested control structures; however, the language does not support recursion. Branching Direct transfer to another paragraph can be accomplished using the GO TO paragraph statement; however, this statement is not used often in COBOL, compared to FORTRAN.

Selection COBOL uses the IF statement for selection. IF condition statement IF condition statement1 ELSE statement2

The conditions in COBOL either condition-items (level 88, described earlier), relational, class, sign or compound. Relational conditions For example, item1 LESS item2 item1 EQUAL item2 item1 GREATER item2 item1 NOT LESS item2 item1 NOT EQUAL item2 item1 NOT GREATER item2 Note: the symbols <, =, or > may be used instead of the words LESS, EQUAL or GREATER. Class conditions This is used for validating input. For example, one can enter non-digits into a numeric data item, but the value will be meaningless for later math (causing a run time error). To avoid this one can check to see that the data in the item is of the correct class, for example, IF dataItem IS NOT NUMERIC statement IF dataItem IS ALPHABETIC statement Sign conditions For example, dataItem IS POSITIVE statement dataItem IS NEGATIVE statement dataItem IS ZERO statement dataItem IS NOT POSITIVE statement dataItem IS NOT NEGATIVE statement dataItem IS NOT ZERO statement Note: an arithmetic expression may be used in place of the dataItem. Compound conditions COBOL includes the boolean operators AND, OR and NOT for building conditions such as IF MY-ITEM IS NUMERIC AND MY-ITEM GREATER 20 COBOL also allows some unusual syntax. For example, A < B OR A < C could be written A < B OR < C or, even, A < B OR C

COBOL allows nested-IF constructs such as IF condition1 IF condition2 statement which gives the possibility of the dangling-ELSE problem. Given, IF condition1 IF condition2 statement1 ELSE statement2 when will statement2 be executed? The rules of COBOL pair an ELSE with the nearest IF that has no ELSE clause. So, statement2 executes when condition1 is true and condition2 is false. If one wanted statement2 to execute when condition1 was false, then a dummy statement can be inserted as follows, IF condition1 IF condition2 statement1 ELSE NEXT SENTENCE ELSE statement2 As usual, typography improves readability: IF condition1 IF condition2 statement1 ELSE NEXT SENTENCE ELSE statement2 Note that the statements can be compound, terminated by a single period.

Repetition The PERFORM verb is used for repetition in COBOL. The PERFORM verb has several forms, such as, PERFORM sentence numericVal TIMES where the numericVal can be either literal values or data items. PERFORM sentence UNTIL condition Even though this looks like a post-test loop, it is not. The condition is tested before the first iteration is PERFORMed. The construct, PERFORM sentence VARYING numericItem FROM numericVal1 BY numericVal2 UNTIL condition implements a counter-controlled loop. Multiple counters can be nested, PERFORM sentence VARYING numericItem1 FROM numericVal1 BY numericVal2 UNTIL condition1 AFTER numericItem2 FROM numericVal3 BY numericVal4 UNTIL condition2

Termination of programs and paragraphs. A COBOL program terminates when the last paragraph in the code is executed, unless termination occurs earlier by the STOP RUN sentence. A COBOL paragraph may be prematurely terminated with the EXIT sentence.

Modularity

COBOL program modules are paragraphs. Each paragraph is executed in order unless that order is superceeded by another control construct. To call a paragraph from within another, PERFORM paragraphName PERFORM paragraphName1 THROUGH paragraphName2 with all of the normal options described above for PERFORM replacing "sentence" with "paragraphName". Note that COBOL does not allow recursion. COBOL also allows separate program files to be used as subprograms. The syntax and semantics of subprograms are not discussed in this handout. The interested reader will wish to use other sources to learn about the CALL verb and the LINKAGE SECTION of the DATA DIVISION in order to learn how several programs can be linked together under the control of one main program.

Input/Output Statements

In COBOL data is normally transferred to and from external files (not interactively). To use external files, several steps are necessary.

1. Create links between logical file names FILE CONTROL and physical files (ENVIRONMENT DIVISION) 2. Create a description of the file FD (DATA DIVISION) 3. Open the files for I/O OPEN (PROCEDURE DIVISION) 4. Use the opened files READ/WRITE (PROCEDURE DIVISION) 5. Close the files when finished CLOSE (PROCEDURE DIVISION)

File Control Each file to be accessed by the program must be declared in the FILE-CONTROL paragraph of the INPUT-OUTPUT SECTION of the ENVIRONMENT DIVISION. In specific, each external file must be declared using the form, ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT logicalFilename ASSIGN TO "systemFilename" For example, an actual select sentence might be, SELECT DATA-FILE ASSIGN TO "COBOL_PROJ.IN" to associate the local file COBOL_PROJ.IN with the program name DATA-FILE.

File Description The FILE SECTION of the DATA DIVISION lays out the format expected/desired for the input/output files in the program. These descriptions follow the same rules as the WORKING-STORAGE descriptions; however, each file must also declare its basic format using an FD description. In general, to read or write to a disk file, this section will be, FILE SECTION. FD logicalFilename LABEL RECORDS ARE STANDARD DATA RECORD IS dataFormat. 01 dataFormat * Normal data description as in previous examles An important addition is available for output files, the LINAGE clause allows one to define the way a page will be laid out. For example, FILE SECTION. FD MY-OUTPUT-FILE LABEL RECORDS ARE STANDARD DATA RECORD IS PRINT-LINE LINAGE IS 52 LINES LINES AT TOP 5 LINES AT BOTTOM 3. 01 PRINT-LINE PIC X(80). which would define output pages to be 60 lines, 5 unused at the top, 3 unused at the bottom and the remainder used for printing the individual lines of output.

Opening files for access The OPEN verb is used to actually activate the file which was previously declared and defined, OPEN INPUT logicalFilename or OPEN OUTPUT logicalFilename Using the files: READ a file, WRITE a record The READ verb is used to get data from the input files, READ logicalFilename AT END statement This causes one record to be read from the file into the dataItem defined in the FILE SECTION. The AT END clause defines the action to be taken if the file READ encounters the end-of-file. Without this clause, the end-of-file could cause a runtime crash. The WRITE verb is used to send data to the output files, WRITE dataItem Note an important difference between reading and writing. In COBOL you READ a file, but WRITE a record. There are some important clauses used with the WRITE verb that control the display of the output. For example, WRITE dataItem BEFORE ADVANCING numericItem LINES WRITE dataItem BEFORE ADVANCING PAGE WRITE dataItem AFTER ADVANCING numericItem LINES WRITE dataItem AFTER ADVANCING PAGE Note the general usage of WRITE involves first constructing the desired data items then placing them all into a generic string which can be printed. This is done by MOVEing various WORKING MEMORY structures into a single structure which is the generic record for all output, typically a single item with a PICTURE such as X(80). See the demo programs for more details.

Closing the files Easy... CLOSE logicalFilenames For example, CLOSE MY-INPUT-FILE, MY-OUTPUT-FILE. Miscellaneous When building print lines, it is often useful to have fields filled with spaces, but it is inconvenient to have to make up unique names for each of these little blocks of space. COBOL includes a RESERVED word FILLER which can be used as often as desired to handle this problem. For example, FILE SECTION. FD MY-OUTPUT-FILE LABEL RECORDS ARE STANDARD DATA RECORD IS PRINT-LINE. 01 PRINT-LINE PIC X(80). WORKING-MEMORY SECTION. 01 ONE-OUTPUT-STYLE. 05 FILLER X(20). 05 THE-DATA $$$$,$$9.99. 05 FILLER X(49). 01 OTHER-OUTPUT-STYLE. 05 FILLER X(30). 05 THE-DATA 999,999.99. 05 FILLER X(40). . . . MOVE 2233.44 TO THE-DATA OF ONE-OUTPUT-STYLE. MOVE ONE-OUTPUT-STYLE TO PRINT-LINE. WRITE PRINT-LINE. MOVE CORRESPONDNING ONE-OUTPUT-STYLE TO OTHER-OUTPUT-STYLE. MOVE OTHER-OUTPUT-STYLE TO PRINT-LINE. WRITE PRINT-LINE. . . . which would result in the output: $2,233.44 002,233.44 Using the two formats, 123456789|123456789|123456789|123456789|123456789|123456789|123456789|123456789| | | | | | | | | <---FILLER X(20)--->$$$$,$$9.99<----------------FILLER X(49)-------------------> <--------FILLER X(30)-------->999,999.99<------------FILLER X(40)-------------->

For further experimentation Several interactive I/O operations are possible. Try experimenting with, DISPLAY "string" [WITH NO ADVANCING] ACCEPT dataItem ACCEPT dataItem FROM DATE YYMMDD format ACCEPT dataItem FROM DAY YYDDD format ACCEPT dataItem FROM TIME HHMMSSVSS format

References

Program boilerplate
Compaq COBOL Reference Manual.
Programming Languages, 2nd ed., Allen B. Tucker, McGraw-Hill, 1986.
Sample programs:
AVERAGE.COB GRADES.COB Prof. Bjork's Demos