Transcript RPG IV - Chapter 5
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
INPUT File SALESFIL Salesman Department Sales Sales date PROCESS OUTPUT Print Heading Initialize variables For each record Read Record Determine Salesman break Subtotal Sales Print Salesman and Sales Accumulate Grand total Print Grand total Heading Report Body Salesman Sales Subtotal Sales Grand total
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