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COBOL
learn.cob

COBOL is a business-oriented language revised multiple times since its original design in 1960.

      *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.
      *The 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) starts 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 Xs can lead to errors,
      *so the above code can be re-written as
       01  MYNAME PIC X(10).

      *Here are some more examples:
       01  AGE             PICTURE  9(3).   *> A number up to 3 digits.
       01  BIRTH_YEAR      PIC      S9(7).  *> A signed number up to 7 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.


      *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'.
      *skip SECOND-PARA and perform 3rd & 4th
      *then after performing THIRD-PARA and FOURTH-PARA,
      *return here and continue the program until STOP RUN.
           PERFORM THIRD-PARA THRU FOURTH-PARA.

           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 (note the order):
      *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 strings.
      *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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