Add comments to CBL0001.cobol

Signed-off-by: klausmelcher <[email protected]>

Author: klausmelcher

Labs/cbl/CBL0001.cobol

@@ -10,6 +10,13 @@
        FILE-CONTROL.
            SELECT PRINT-LINE ASSIGN TO PRTLINE.
            SELECT ACCT-REC   ASSIGN TO ACCTREC.
+      *SELECT clause creates an internal file name
+      *ASSIGN clause creates a name for an external data source,
+      *which is associated with the JCL DDNAME used by the z/OS
+      *e.g. ACCTREC is linked in JCL file CBL0001J to &SYSUID..DATA 
+      *where &SYSUID. stands for Your z/OS user id
+      *e.g. if Your user id is Z54321,
+      *the data set used for ACCTREC is Z54321.DATA	
       *-------------
        DATA DIVISION.
       *-------------
@@ -19,15 +26,22 @@
            05  ACCT-NO-O      PIC X(8).
            05  ACCT-LIMIT-O   PIC $$,$$$,$$9.99.
            05  ACCT-BALANCE-O PIC $$,$$$,$$9.99.
+      * PIC $$,$$$,$$9.99 -- Alternative for PIC on chapter 7.2.3,
+      * using $ to allow values of different amounts of digits
+      * and .99 instead of v99 to allow period display on output 
            05  LAST-NAME-O    PIC X(20).
            05  FIRST-NAME-O   PIC X(15).
            05  COMMENTS-O     PIC X(50).
+      * since the level 05 is higher than level 01, 
+      * all variables belong to PRINT-REC (see chapter 7.3.3)
       *
        FD  ACCT-REC RECORDING MODE F.
        01  ACCT-FIELDS.
            05  ACCT-NO            PIC X(8).
            05  ACCT-LIMIT         PIC S9(7)V99 COMP-3.
            05  ACCT-BALANCE       PIC S9(7)V99 COMP-3.
+      * PIC S9(7)v99 -- seven-digit plus a sign digit value
+      * COMP-3 -- packed BCD (binary coded decimal) representation
            05  LAST-NAME          PIC X(20).
            05  FIRST-NAME         PIC X(15).
            05  CLIENT-ADDR.
@@ -49,6 +63,11 @@
       *
        READ-NEXT-RECORD.
            PERFORM READ-RECORD
+      *     The previous statement is needed before entering the loop.
+      *     Both the loop condition LASTREC = 'Y'
+      *     and the call to WRITE-RECORD depend on READ-RECORD having
+      *     been executed before.
+      *     The loop starts at the next line with PERFORM UNTIL
             PERFORM UNTIL LASTREC = 'Y'
             PERFORM WRITE-RECORD
             PERFORM READ-RECORD