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Corrections and some added explanation.
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Mark Green
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@ -7,12 +7,13 @@ filename: learn.COB
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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
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organizations.
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```
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```cobol
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*COBOL. Coding like it's 1985.
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*Compiles with GnuCOBOL in OpenCobolIDE 4.7.6.
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*COBOL has significant differences between legacy (COBOL-85)
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*and modern (COBOL-2002 and COBOL-2014) versions.
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*Legacy versions require columns 1-6 to be blank (they are used
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*Legacy versions require columns 1-6 to be blank (they are used
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*to store the index number of the punched card..)
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*A * in column 7 means a comment.
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*In legacy COBOL, a comment can only be a full line.
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@ -21,9 +22,9 @@ organizations.
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*Legacy COBOL also imposes a limit on maximum line length.
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*Keywords have to be in capitals in legacy COBOL,
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*but are case insensitive in modern.
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*First, we must give our program ID.
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*Identification division can include other values too,
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*Identification division can include other values too,
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*but they are comments only. Program-id is mandatory.
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identification division.
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program-id. learn.
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@ -32,7 +33,7 @@ organizations.
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data division.
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working-storage section.
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*Variables are specified by a "picture" - how they should be
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*Variables are specified by a "picture" - how they should be
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*displayed, and variable type is inferred from this.
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*The "01" value is the level number which is used for building
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*data structures.
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@ -40,9 +41,9 @@ organizations.
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01 age picture 999. *> A number up to 3 digits.
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01 valx picture 999. *> Another number up to 3 digits.
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01 inyear picture s9(7). *> S makes number signed.
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*> Brackets indicate 6 repeats of 9,
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*> Brackets indicate 7 repeats of 9,
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*> ie a 6 digit number (not an array).
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*Now let's write some code.
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procedure division.
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@ -64,98 +65,104 @@ organizations.
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display age *> Left-padded to three chracaters with zeroes,
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*> because of the defined PICTURE for age.
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*> We have two ways of doing a FOR loop.
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*> Old style way: doesn't give an index.
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perform age times
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display "*" with no advancing *> Ie, no newline at end
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end-perform.
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end-perform
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display "." *> Output buffer isn't flushed until newline.
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*> New style way: with an index.
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perform varying valx from 1 by 1 until valx > age
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display valx "-" with no advancing
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end-perform.
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perform varying valx from 1 by 1 until valx > age
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display valx "-" with no advancing
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end-perform
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display "."
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*> If tests are still good old if tests.
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if myname = "Bob" then
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if myname = "Bob" then
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display "I don't like Bob."
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else
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display "I don't know you."
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end-if
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*> There are two ways of doing subprograms and calling
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else
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display "I don't know you."
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end-if
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*> There are two ways of doing subprograms and calling
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*> them.
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*> The simplest way: a paragraph.
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perform subparagraph
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*> The complex way, with parameters and stuff.
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call "eratosthenes" using age returning valx
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call "eratosthenes" using age returning valx
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display "There were " valx " primes."
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stop run.
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subparagraph. *> Marks the top of an internal subprogram.
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*> Shares variable score with its caller.
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*> Read year from system timer.
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*> Remember the whole "year 2000 crisis"? The yyyyddd
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*> option was added in response to that.
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accept inyear from day yyyyddd.
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*> We can do math step-by-step like this...
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divide 1000 into inyear.
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divide 1000 into inyear.
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subtract age from inyear.
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display "You were born in " inyear "."
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*> Or we can just use expressions.
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compute inyear = 1970 - inyear.
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*> Note: if inyear has gone negative, its negativity will
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*> not appear when printed, because we didn't include an
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*> S (sign character) in the PICTURE.
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if inyear >= 0 then
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if inyear >= 0 then
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display "When you were " inyear ", " with no advancing
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else
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display inyear " years before you were born, " with no
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advancing
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end-if
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display "COBOL was the most popular language in the world."
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.
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display "COBOL was the most popular language in the world."
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. *> You can put the final . on a new line if it's clearer.
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*If we want to use a subprogram, we use literally a subprogram.
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*This is the entire program layout, repeated for the
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*eratosthenes subroutine.
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identification division.
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program-id. eratosthenes.
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data division.
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working-storage section.
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*Declare an array.
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*We can declare a variable to use as an index for it at the
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*Declare an array.
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*We can declare a variable to use as an index for it at the
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*same time.
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01 sieve pic 9 occurs 999 times indexed by sa, sb.
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*> Standard cobol doesn't have a boolean type.
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01 pstart pic 999.
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01 counter pic 999.
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*Our parameters have to be declared in the linkage section.
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*Their pictures must match the values they're called with.
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linkage section.
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01 maxvalue picture 999.
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*"using" declares our actual parameter variables.
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*"using" declares our actual parameter variables.
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*"returning" declares the variable value returned at end.
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procedure division using maxvalue returning counter.
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main-procedure.
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display "Here are all the primes up to " maxvalue "."
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perform varying sa from 1 by 1 until sa > maxvalue
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move 1 to sieve (sa)
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end-perform
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end-perform
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perform varying sa from 2 by 1 until sa > maxvalue
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if sieve(sa) = 1 then
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if sieve(sa) = 1 then
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compute pstart = sa + sa
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perform varying sb from pstart by sa until sb >
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maxvalue
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perform varying sb from pstart by sa until sb >
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maxvalue
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move 0 to sieve(sb)
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end-perform
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end-if
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@ -163,17 +170,17 @@ organizations.
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initialise counter *> To zero by default for a number.
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perform varying sa from 2 by 1 until sa > maxvalue
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perform varying sa from 2 by 1 until sa > maxvalue
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if sieve(sa) = 1 THEN
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display sa
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add 1 to counter
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end-if
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end-if
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end-perform.
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end program eratosthenes.
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end program eratosthenes.
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end program learn.
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```
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##Ready For More?
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