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RPG IV

RPG IV. Top-Down, Structured Program Design - Chapter 5. Objectives :. Determine how to design and write structured RPG programs Use structured RPG operations that perform sequence, selection, and iteration Use subroutines Design a control break program. Structured Design.

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RPG IV

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  1. RPG IV Top-Down, Structured Program Design - Chapter 5

  2. Objectives: • Determine how to design and write structured RPG programs • Use structured RPG operations that perform sequence, selection, and iteration • Use subroutines • Design a control break program

  3. Structured Design • A methodology that limits its control to 3 basic structures: • Sequence • Selection • Iteration • Each of these control structures has a single entry point and a single exit point

  4. Sequence Control Structure

  5. Selection Control Structure

  6. Iteration Control Structure

  7. Relational Codes Symbol Code Meaning > GT Greater than < LT Less than = EQ Equal to <> NE Not equal to <= LE Less than or equal to >= GE Greater than or equal to

  8. Collating sequence • Character by character comparison • EBCDIC • Digits are compared based on algebraic value • Letters are smaller than digits • Lowercase letters are smaller then uppercase letters • A blank is smaller than any other displayable character

  9. Selection Operations • IF Conditional expression - ENDIF • IF Conditional expression - ELSE - ENDIF • AND - OR • Nested Ifs (Case logic) • SELECT - ENDSL • CASxx - ENDCS

  10. IF - ENDIF • If the comparison is true all statements between the IF and ENDIF are performed • If the comparison is false the statements are bypassed

  11. IF - ELSE - ENDIF • If the comparison is true all statements between the IF and ELSE are performed • If the comparison is false all the statements between the ELSE and the ENDIF are performed

  12. AND - OR • AND, both relationships must be true • OR, one or the other or both relationships must be true

  13. Nested IFs • Build IFs within Ifs

  14. IF and Page Overflow • Built in indicators called overflow indicators • OA thru OG and OV • Use the Keyword OFLIND in the File Specification to make the association between the indicator and report file • The indicator will automatically come on when the printer reaches the overflow line at the bottom of the page

  15. SELECT • Appears on a line alone to identify the start of a case construct • The SELECT is followed by one or more WHEN, each of which specifies a conditions to be tested • Each WHEN is followed by one or more statements to be performed • WHEN conditions can be coupled with AND and/or OR operations

  16. SELECT cont • OTHER means ‘in all other cases’ • OTHER should be the final catch all • As soon as it encounters a true condition, the computer executes the operation(s) following a WHEN • Control is then sent to the end of SELECT, signaled by an ENDSL

  17. CASxx • Nearly identical to SELEC • CASxx operation sends control to subroutines • Use ENDCS to signal end of CASxx

  18. Iteration Operations • DOW Conditional expression - ENDDO • DOU Conditional expression - ENDDO • DO - ENDDO • FOR - ENDFOR

  19. Do While Loop

  20. DOW • This operation establishes a loop, based on a comparison • Test is made at the beginning of loop • All operations coded between this operator and ENDDO are repeated as long as the condition specified in the relational comparison remains true • The DOW allows you to use AND and OR to form compound conditions

  21. Do Until Loop

  22. DOU • The DOU is a structure iteration operation very similar to DOW • The DOW repeats while the specified conditions remains true • The DOU repeats until the condition becomes true • DOU the comparison is made after the instructions in the loop have been executed

  23. DO • Designed specifically for count-controlled loops • Specify four things: • starting value of counter • limit value of counter • counter • increment value to be added to counter • You can omit any of the four, default value is 1

  24. DO cont • Factor 1 on the DO is the starting value of counter • Factor 2 on the DO is the limit value of counter • Result on the DO is the counter • Factor 2 on the ENDDO is the increment value to be added to counter

  25. FOR • FOR is a free-form replacement for the DO operation • Like DO, FOR is a count-controlled loop instruction

  26. Early Exits from Loops • ITER • When ITER is encountered within a loop, control skips past the remaining instructions in the loop and causes the next repetition to begin • LEAVE • Terminates the looping process and sends the control to the statements following the ENDDO

  27. Subroutines • BEGSR/ENDSR • EXSR

  28. BEGSR/ENDSR • Block of code with an identifiable beginning and end • Subroutines are identified by the (optional) letters SR in positions 7-8 of a line, • The name of the subroutine in factor 1 and the operation BEGSR • The last line of a subroutine is a line containing ENDSR in the operation

  29. BEGSR/ENDSR cont • Subroutines must have a unique name formed with the same rules that apply to fields • Subroutines may execute other subroutines, but a subroutine should never execute itself • Subroutines cannot contain other subroutines

  30. EXSR • Execute subroutine • Enter the name of the subroutine to be performed in factor 2

  31. Control Break IPO

  32. Control Break Hierarchy 0000-Mainline 1000-Initial 3000-SlspBreak 5000-Detail 7000-Terminate 3000-SlspBreak

  33. Control Break Logic:0000-MainLine Do Initialization Routine WHILE not end-of file IF change in salesperson Do SlspBreak Routine ENDIF Do Detail Process Routine Read next record ENDWHILE Do Termination Routine END Program

  34. Control Break Logic: 1000-Initial Read first record Set up hold area Print Headings END routine

  35. Control Break Logic:3000-Slspbreak Print salesperson line Add salesperson’s total to grand total Zero out salesperson’s total Move new value to hold area END routine

  36. Control Break Logic:5000-Detail IF page overflow Print headings ENDIF Print detail line Accumulate sales in salesperson’s total END routine

  37. Control Break Logic: 7000-Terminate Do Slspbreak Routine Print grand total END Routine

  38. Sample Program - F Specs *..1....+....2....+....3....+....4....+....5....+....6....+....7....+....8 F************************************************************************** F* Program :R0400HOK * F* Name :Yeager, Meyers & Kronholm * F* Description :This program produces a Sales Report Listing subtotal * F* for each salesman * F* Indicators :OF - Overflow * F* LR - Last Record * F* * F************************************************************************** *..1....+....2....+....3....+....4....+....5....+....6....+....7....+....8 F*ilename++IP FRlen+ Device * FSalesFile IF F 19 DISK FQPRINT O F 132 PRINTER OFLIND(*INOF)

  39. Sample Program - D & I Specs D************************************************************************** D* Definition of all work fields used in program. * D************************************************************************** *..1....+....2....+....3....+....4....+....5....+....6....+....7....+....8 D*Name++++++++++ Ds Len+ Dc D HoldSlsp S 4 D SlspTotal S 6 2 INZ(0) D GrandTotal S 8 2 INZ(0) I************************************************************************** I* Input file of received items defined within the program. * I************************************************************************** *..1....+....2....+....3....+....4....+....5....+....6....+....7....+....8 I*ilename++Sq ISalesFile NS *..1....+....2....+....3....+....4....+....5....+....6....+....7....+....8 I* From+To+++DcField+++++++++ I 1 4 SalesPrsn I 5 7 Dept I 8 13 2SalesAmt

  40. Sample Program - C Specs C************************************************************************** C* OOOO-Mainline * C* Calculations required to produce the sales report * C************************************************************************** C EXSR Initial C* C DOW Not %EOF(SalesFile) C IF HoldSlsp <> SalesPrsn C EXSR SlspBreak C ENDIF C EXSR Detail C READ SalesFile 90 C ENDDO C* C ESXR Terminate C EVAL *INLR = *ON C RETURN

  41. Sample Program - C Specs C************************************************************************** C* 1000-Initial * C* Subroutine to read first record, set up hold salesman, and print * C* first page heading. * C************************************************************************** CSR Initial BEGSR C READ SalesFile 90 C EVAL HoldSlsp = SalesPrsn C EXCEPT Headings C ENDSR

  42. Sample Program - C Specs C************************************************************************** C* 3000-SlspBreak * C* Subroutine done when salesman changes; print subtotal, rollover * C* accumulator, zero out accumulator, and reset hold * C************************************************************************** CSR SlspBreak BEGSR C EXCEPT BreakLine C EVAL GrandTotal = GrandTotal + SlspTotal C EVAL SlspTotal = 0 C EVAL HoldSlsp = SalesPrsn C ENDSR

  43. Sample Program - C Specs C************************************************************************** C* 5000-Detail * C* Subroutine executed for each input record * C************************************************************************** CSR Detail BEGSR C IF *INOF = *ON C EXCEPT Headings C EVAL *INOF = *OFF C ENDIF C* C EXCEPT DetailLine C EVAL SlspTotal = SlspTotal + SalesAmt C ENDSR

  44. Sample Program - C Specs C************************************************************************** C* 7000-Terminate * C* Subroutine done at end of file; execute SlspBreak one last time* C* and print grand total line. * C************************************************************************** CSR Terminate BEGSR C EXSR SlspBreak C EXCEPT TotalLine C ENDSR

  45. Sample Program - O Specs *..1....+....2....+....3....+....4....+....5....+....6....+....7....+....8 O*ilename++D ExceptnameB++A++Sb+Sa+ OQPRINT E Headings 2 2 *..1....+....2....+....3....+....4....+....5....+....6....+....7....+....8 O* Field+++++++++Y End++ Constant/Editword+++++++++++ O 8 ‘R0400HOK’ O* *DATE is a four digit year. O *DATE Y 20 O 33 ’SALES REPORT' O 40 'PAGE' O PAGE Z 44 O E Headings 2 O 20 ’SLSPSN.' O 37 ’AMT.' O** Detail Line ** O E DetailLine 1 O SalesPrsn 18 O SalesAmt 1 39

  46. Sample Program - O Specs *..1....+....2....+....3....+....4....+....5....+....6....+....7....+....8 O*ilename++D ExceptnameB++A++Sb+Sa+ O E BreakLine 1 2 *..1....+....2....+....3....+....4....+....5....+....6....+....7....+....8 O* Field+++++++++Y End++ Constant/Editword+++++++++++ O 24 ‘TOTAL’ O SlspTotal 1 39 O 40 ‘*’ *..1....+....2....+....3....+....4....+....5....+....6....+....7....+....8 O*ilename++D ExceptnameB++A++Sb+Sa+ O E TotalLine *..1....+....2....+....3....+....4....+....5....+....6....+....7....+....8 O* Field+++++++++Y End++ Constant/Editword+++++++++++ O 26 'GRAND TOTAL' O GrandTotal 1 39 O 41 ‘**’

  47. Points to Remember • Structured program design means developing program logic with flow of control tightly managed, generally by using only structured operations • Top-down methodology requires that you approach designing your program hierarchically, working out its broad logic first and later attending to the detailed processing requirements

  48. Points to Remember (cont) • RPG provides structured operations IF, CASxx, and SELECT to implements decision logic • Structured operations DOW, DOU, DO and FOR to implement looping logic • Most of the structured operation of RPG require the use of one of six relational operators • The operators are: GT, LT, EQ, NE, LE, GE

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