Merge pull request #3900 from hyphz/master

[en-en/cobol] Added COBOL. With all the current press, I think this is inevitable.. I'm not an expert, but it's a start.

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+---
+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. Coding like it's 1985.
+       
+      *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 6 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.
+           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.
+           
+           *> Note: if inyear has gone negative, its negativity will
+           *> not appear when printed, because we didn't include an 
+           *> S (sign character) in the PICTURE.
+           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."         
+           .
+           
+           
+       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.
+       01  pstart pic 999.
+       01  counter pic 999.
+            
+      *Our parameters have to be declared in the linkage section.
+       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/)
+