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diff --git a/cobol.html.markdown b/cobol.html.markdown index 4452bd95..7d94d8c9 100644 --- a/cobol.html.markdown +++ b/cobol.html.markdown @@ -8,178 +8,187 @@ COBOL is a business-oriented language revised multiple times since its original organizations. ```cobol - *COBOL. Coding like it's 1985. + *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. + *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. - - *First, we must give our program ID. + *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 DIVSION. + *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 mandatory. - identification division. - program-id. learn. + *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. - data division. - working-storage section. - - *Variables are specified by a "picture" - how they should be - *displayed, and variable type is inferred from this. - *The "01" value is the level number which is used for building - *data structures. - 01 myname picture xxxxxxxxxx. *> A 10 character string. - 01 age picture 999. *> A number up to 3 digits. - 01 valx picture 999. *> Another number up to 3 digits. - 01 inyear picture s9(7). *> S makes number signed. + *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. - procedure division. - - main-procedure. - *> COBOL is the language that uses DISPLAY instead of PRINT. - *> Note: no full stops after commands. Only after the LAST - *> command. - display "Hello. What's your name?" - - *> Let's input a string. - *> If input too long, later characters are trimmed. - accept myname - display "Hello " myname *> We can display several things. - display "How old are you?" - - *> Let's input a number. - *> If input too long, EARLIER characters are trimmed. - accept age - - display age *> Left-padded to three chracaters with zeroes, - *> because of the defined PICTURE for age. - - *> We have two ways of doing a FOR loop. - *> Old style way: doesn't give an index. - perform age times - display "*" with no advancing *> Ie, no newline at end - end-perform - display "." *> Output buffer isn't flushed until newline. - - *> New style way: with an index. - perform varying valx from 1 by 1 until valx > age - display valx "-" with no advancing - end-perform - display "." - - *> If tests are still good old if tests. - if myname = "Bob" then - display "I don't like Bob." - else - display "I don't know you." - end-if - - *> There are two ways of doing subprograms and calling - *> them. - *> The simplest way: a paragraph. - perform subparagraph - - *> The complex way, with parameters and stuff. - call "eratosthenes" using age returning valx - - display "There were " valx " primes." - - stop run. - - subparagraph. *> Marks the top of an internal subprogram. - *> Shares variable score with its caller. - - *> Read year from system timer. - *> Remember the whole "year 2000 crisis"? The yyyyddd - *> option was added in response to that. - accept inyear from day yyyyddd. - - *> We can do math step-by-step like this... - divide 1000 into inyear. - subtract age from inyear. - - display "You were born in " inyear "." - - *> Or we can just use expressions. - compute inyear = 1970 - inyear. - - if inyear >= 0 then - display "When you were " inyear ", " with no advancing - else - display inyear " years before you were born, " with no - advancing - end-if - - display "COBOL was the most popular language in the world." - . *> You can put the final . on a new line if it's clearer. - - - *If we want to use a subprogram, we use literally a subprogram. - *This is the entire program layout, repeated for the - *eratosthenes subroutine. - identification division. - program-id. eratosthenes. - - data division. - working-storage section. - *Declare an array. - *We can declare a variable to use as an index for it at the - *same time. - 01 sieve pic 9 occurs 999 times indexed by sa, sb. - *> Standard cobol doesn't have a boolean type. - 01 pstart pic 999. - 01 counter pic 999. - - *Our parameters have to be declared in the linkage section. - *Their pictures must match the values they're called with. - linkage section. - 01 maxvalue picture 999. - - *"using" declares our actual parameter variables. - *"returning" declares the variable value returned at end. - procedure division using maxvalue returning counter. - main-procedure. - - display "Here are all the primes up to " maxvalue "." - - perform varying sa from 1 by 1 until sa > maxvalue - move 1 to sieve (sa) - end-perform - - perform varying sa from 2 by 1 until sa > maxvalue - if sieve(sa) = 1 then - compute pstart = sa + sa - perform varying sb from pstart by sa until sb > - maxvalue - move 0 to sieve(sb) - end-perform - end-if - end-perform - - initialise counter *> To zero by default for a number. - - perform varying sa from 2 by 1 until sa > maxvalue - if sieve(sa) = 1 THEN - display sa - add 1 to counter - end-if - end-perform. - - end program eratosthenes. - - end program learn. + *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 DIVSION. + 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 + + + + + ``` |