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Update to cobol.html.markdown

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Fixed multiple errors in the COBOL tutorial.
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Hunter Coleman 2020-05-02 14:20:19 -05:00 committed by Andrew Ryan Davis
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@ -8,7 +8,7 @@ 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)
@ -22,164 +22,161 @@ organizations.
*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 DIVSION.
*ENVIRONMENT DIVISION.
*DATA DIVISION.
*PROCEDURE DIVISION.
*First, we must give our program ID.
*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.
*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.
*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
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?"
********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.
*> 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?"
IDENTIFICATION DIVISION.
PROGRAM-ID. HELLOCOBOL.
*> Let's input a number.
*> If input too long, EARLIER characters are trimmed.
accept age
PROCEDURE DIVISION.
FIRST-PARA.
DISPLAY 'THIS IS IN FIRST-PARA'.
PERFORM THIRD-PARA THRU FOURTH-PARA. *>skip over second-para and perfrom third and fourth
*> 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.
display age *> Left-padded to three chracaters with zeroes,
*> because of the defined PICTURE for age.
*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.
*> 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.
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.
*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.
*The above code will output:
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.
THE FULL NAME IS: BOB COBB
*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.
*Let’s examine it to see why.
display "Here are all the primes up to " maxvalue "."
*First, we declared all of our variables, including the one that we are creating by the string command, in the DATA DIVISISION.
perform varying sa from 1 by 1 until sa > maxvalue
move 1 to sieve (sa)
end-perform
*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
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.
```