diff --git a/cobol.html.markdown b/cobol.html.markdown
index b0ab5b6d..4452bd95 100644
--- a/cobol.html.markdown
+++ b/cobol.html.markdown
@@ -7,12 +7,13 @@ 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
+ *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.
@@ -21,9 +22,9 @@ 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.
-
+
*First, we must give our program ID.
- *Identification division can include other values too,
+ *Identification division can include other values too,
*but they are comments only. Program-id is mandatory.
identification division.
program-id. learn.
@@ -32,7 +33,7 @@ organizations.
data division.
working-storage section.
- *Variables are specified by a "picture" - how they should be
+ *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.
@@ -40,9 +41,9 @@ organizations.
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,
+ *> Brackets indicate 7 repeats of 9,
*> ie a 6 digit number (not an array).
-
+
*Now let's write some code.
procedure division.
@@ -64,98 +65,104 @@ organizations.
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.
+ 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.
+ 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
+ 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
+ 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
-
+ 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.
+ 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
+
+ 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."
- .
-
-
+
+ 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
+ *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.
+
+ *"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
-
+ end-perform
+
perform varying sa from 2 by 1 until sa > maxvalue
- if sieve(sa) = 1 then
+ if sieve(sa) = 1 then
compute pstart = sa + sa
- perform varying sb from pstart by sa until sb >
- maxvalue
+ perform varying sb from pstart by sa until sb >
+ maxvalue
move 0 to sieve(sb)
end-perform
end-if
@@ -163,17 +170,17 @@ organizations.
initialise counter *> To zero by default for a number.
- perform varying sa from 2 by 1 until sa > maxvalue
+ perform varying sa from 2 by 1 until sa > maxvalue
if sieve(sa) = 1 THEN
display sa
add 1 to counter
- end-if
+ end-if
end-perform.
-
- end program eratosthenes.
-
+
+ end program eratosthenes.
+
end program learn.
-
+
```
##Ready For More?