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| language | contributors | filename | |||
|---|---|---|---|---|---|
| COBOL |
|
learn.COB |
COBOL is a business-oriented language revised multiple times since its original design in 1960. It is claimed to still be used in over 80% of organizations.
*COBOL. Coding like it's 1985.
*Compiles with GnuCOBOL in OpenCobolIDE 4.7.6.
*COBOL has significant differences between legacy (COBOL-85)
*and modern (COBOL-2002 and COBOL-2014) versions.
*Legacy versions require columns 1-6 to be blank (they are used
*to store the index number of the punched card..)
*A '*' in column 7 means a comment.
*In legacy COBOL, a comment can only be a full line.
*Modern COBOL doesn't require fixed columns and uses *> for
*a comment, which can appear in the middle of a line.
*Legacy COBOL also imposes a limit on maximum line length.
*Keywords have to be in capitals in legacy COBOL,
*but are case insensitive in modern.
*Although modern COBOL allows you to use mixed-case characters
*it is still common to use all caps when writing COBOL code.
*This is what most professional COBOL developers do.
*COBOL statements end with a period.
*COBOL code is broken up into 4 divisions.
*Those divisions, in order, are:
*IDENTIFICATION DIVISION.
*ENVIRONMENT DIVISION.
*DATA DIVISION.
*PROCEDURE DIVISION.
*First, we must give our program an ID.
*Identification division can include other values too,
*but they are comments only. Program-id is the only one that is mandatory.
IDENTIFICATION DIVISION.
PROGRAM-ID. LEARN.
AUTHOR. JOHN DOE.
DATE-WRITTEN. 05/02/2020.
*Let's declare some variables.
*We do this in the WORKING-STORAGE section within the DATA DIVISION.
*Each data item (aka variable) with start with a level number,
*then the name of the item, followed by a picture clause
*describing the type of data that the variable will contain.
*Almost every COBOL programmer will abbreviate PICTURE as PIC.
*A is for alphabetic, X is for alphanumeric, and 9 is for numeric.
*example:
01 MYNAME PIC xxxxxxxxxx. *> A 10 character string.
*But counting all those x's can lead to errors,
*so the above code can, and should
*be re-written as:
01 MYNAME PIC X(10).
*Here are some more examples:
01 AGE PIC 9(3). *> A number up to 3 digits.
01 LAST_NAME PIC X(10). *> A string up to 10 characters.
*In COBOL, multiple spaces are the same as a single space, so it is common
*to use multiple spaces to line up your code so that it is easier for other
*coders to read.
01 inyear picture s9(7). *> S makes number signed.
*> Brackets indicate 7 repeats of 9,
*> ie a 6 digit number (not an array).
*Now let's write some code. Here is a simple, Hello World program.
IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 THE-MESSAGE PIC X(20).
PROCEDURE DIVISION.
DISPLAY "STARTING PROGRAM".
MOVE "HELLO WORLD" TO THE-MESSAGE.
DISPLAY THE-MESSAGE.
STOP RUN.
*The above code will output:
*STARTING PROGRAM
*HELLO WORLD
********COBOL can perform math***************
ADD 1 TO AGE GIVING NEW-AGE.
SUBTRACT 1 FROM COUNT.
DIVIDE VAR-1 INTO VAR-2 GIVING VAR-3.
COMPUTE TOTAL-COUNT = COUNT1 PLUS COUNT2.
*********PERFORM********************
*The PERFORM keyword allows you to jump to another specified section of the code,
*and then to return to the next executable
*statement once the specified section of code is completed.
*You must write the full word, PERFORM, you cannot abbreviate it.
IDENTIFICATION DIVISION.
PROGRAM-ID. HELLOCOBOL.
PROCEDURE DIVISION.
FIRST-PARA.
DISPLAY 'THIS IS IN FIRST-PARA'.
PERFORM THIRD-PARA THRU FOURTH-PARA. *>skip second-para and perfrom 3rd & 4th
*> then after performing third and fourth,
*> return here and continue the program until STOP RUN.
SECOND-PARA.
DISPLAY 'THIS IS IN SECOND-PARA'.
STOP RUN.
THIRD-PARA.
DISPLAY 'THIS IS IN THIRD-PARA'.
FOURTH-PARA.
DISPLAY 'THIS IS IN FOURTH-PARA'.
*When you compile and execute the above program, it produces the following result:
THIS IS IN FIRST-PARA
THIS IS IN THIRD-PARA
THIS IS IN FOURTH-PARA
THIS IS IN SECOND-PARA
**********Combining variables together using STRING ***********
*Now it is time to learn about two related COBOL verbs: string and unstring.
*The string verb is used to concatenate, or put together, two or more stings.
*Unstring is used, not surprisingly, to separate a
*string into two or more smaller strings.
*It is important that you remember to use ‘delimited by’ when you
*are using string or unstring in your program.
IDENTIFICATION DIVISION.
PROGRAM-ID. LEARNING.
ENVIRONMENT DIVISION.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 FULL-NAME PIC X(20).
01 FIRST-NAME PIC X(13) VALUE "BOB GIBBERISH".
01 LAST-NAME PIC X(5) VALUE "COBB".
PROCEDURE DIVISION.
STRING FIRST-NAME DELIMITED BY SPACE
" "
LAST-NAME DELIMITED BY SIZE
INTO FULL-NAME
END-STRING.
DISPLAY "THE FULL NAME IS: "FULL-NAME.
STOP RUN.
*The above code will output:
THE FULL NAME IS: BOB COBB
*Let’s examine it to see why.
*First, we declared all of our variables, including the one that we are creating
*by the string command, in the DATA DIVISION.
*The action takes place down in the PROCEDURE DIVISION.
*We start with the STRING keyword and end with END-STRING. In between we
*list what we want to combine together into the larger, master variable.
*Here, we are combining FIRST-NAME, a space, and LAST-NAME.
*The DELIMITED BY phrase that follows FIRST-NAME and
*LAST-NAME tells the program how much of each variable we want to capture.
*DELIMITED BY SPACE tells the program to start at the beginning,
*and capture the variable until it runs into a space.
*DELIMITED BY SIZE tells the program to capture the full size of the variable.
*Since we have DELIMITED BY SPACE after FIRST-NAME, the GIBBERISH part is ignored.
*To make this clearer, change line 10 in the above code to:
STRING FIRST-NAME DELIMITED BY SIZE
*and then re-run the program. This time the output is:
THE FULL NAME IS: BOB GIBBERISH COBB
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