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diff --git a/cobol.html.markdown b/cobol.html.markdown new file mode 100644 index 00000000..4452bd95 --- /dev/null +++ b/cobol.html.markdown @@ -0,0 +1,189 @@ +--- +language: COBOL +contributors: + - ["Hyphz", "http://github.com/hyphz/"] +filename: 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 + *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. + + *First, we must give our program ID. + *Identification division can include other values too, + *but they are comments only. Program-id is mandatory. + identification division. + program-id. learn. + + *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. + *> 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. + +``` + +##Ready For More? + +* [GnuCOBOL](https://sourceforge.net/projects/open-cobol/) + |