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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

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

  • 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


Sequence Control Structure


Selection Control Structure


Iteration Control Structure


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


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


Selection Operations

  • IF Conditional expression - ENDIF

  • IF Conditional expression - ELSE - ENDIF

  • AND - OR

  • Nested Ifs (Case logic)

  • SELECT - ENDSL

  • CASxx - ENDCS


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


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


AND - OR

  • AND, both relationships must be true

  • OR, one or the other or both relationships must be true


Nested IFs

  • Build IFs within Ifs


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


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


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


CASxx

  • Nearly identical to SELEC

  • CASxx operation sends control to subroutines

  • Use ENDCS to signal end of CASxx


Iteration Operations

  • DOW Conditional expression - ENDDO

  • DOU Conditional expression - ENDDO

  • DO - ENDDO

  • FOR - ENDFOR


Do While Loop


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


Do Until Loop


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


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


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


FOR

  • FOR is a free-form replacement for the DO operation

  • Like DO, FOR is a count-controlled loop instruction


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


Subroutines

  • BEGSR/ENDSR

  • EXSR


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


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


EXSR

  • Execute subroutine

  • Enter the name of the subroutine to be performed in factor 2


Control Break IPO


Control Break Hierarchy

0000-Mainline

1000-Initial

3000-SlspBreak

5000-Detail

7000-Terminate

3000-SlspBreak


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


Control Break Logic: 1000-Initial

Read first record

Set up hold area

Print Headings

END routine


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


Control Break Logic:5000-Detail

IF page overflow

Print headings

ENDIF

Print detail line

Accumulate sales in salesperson’s total

END routine


Control Break Logic: 7000-Terminate

Do Slspbreak Routine

Print grand total

END Routine


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)


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


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


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


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


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


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


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


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 ‘**’


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


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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