03 FILLER PIC X(38) VALUE "SDSouth Dakota Pierre 00833354".
03 FILLER PIC X(38) VALUE "TNTennessee Nashville 06456243".
03 FILLER PIC X(38) VALUE "TXTexas Austin 26059203".
03 FILLER PIC X(38) VALUE "UTUtah Salt Lake City02855287".
03 FILLER PIC X(38) VALUE "VTVermont Montpelier 00626011".
03 FILLER PIC X(38) VALUE "VAVirginia Richmond 08185867".
03 FILLER PIC X(38) VALUE "WAWashington Olympia 06897012".
03 FILLER PIC X(38) VALUE "WVWest Virginia Charleston 01855413".
03 FILLER PIC X(38) VALUE "WIWisconsin Madison 05726398".
03 FILLER PIC X(38) VALUE "WYWyoming Cheyenne 00576412".
02 FILLER REDEFINES StateValues.
03 State OCCURS 50 TIMES
INDEXED BY StateIdx.
04 StateCode PIC XX.
04 StateName PIC X(14).
04 StateCapital PIC X(14).
04 StatePop PIC 9(8).
LINKAGE SECTION.
01 StateNum-IO PIC 99.
88 ValidStateNum VALUE 1 THRU 50.
01 StateCode-IO PIC XX.
01 StateName-IO PIC X(14).
01 StateCapital-IO PIC X(14).
01 StatePop-IO PIC 9(8).
01 ErrorFlag PIC 9.
88 NoErrorFound VALUE ZERO.
88 InvalidStateNum VALUE 1.
88 NoSearchItems VALUE 2.
88 NoSuchStateCode VALUE 3.
88 NoSuchStateName VALUE 4.
88 NoSuchCapital VALUE 5.
PROCEDURE DIVISION USING StateNum-IO, StateCode-IO, StateName-IO,
StateCapital-IO, StatePop-IO, ErrorFlag.
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Chapter 16 ■ Creating Large SyStemS
Begin.
SET NoErrorFound TO TRUE
SET StateIdx TO 1
EVALUATE TRUE
WHEN StateNum-IO NOT EQUAL ZEROS PERFORM SearchUsingStateNum
WHEN StateCode-IO NOT EQUAL SPACES PERFORM SearchUsingStateCode
WHEN StateName-IO NOT EQUAL SPACES PERFORM SearchUsingStateName
WHEN StateCapital-IO NOT EQUAL SPACES PERFORM SearchUsingStateCapital
WHEN OTHER SET NoSearchItems TO TRUE
END-EVALUATE
EXIT PROGRAM.
SearchUsingStateNum.
IF NOT ValidStateNum SET InvalidStateNum TO TRUE
ELSE
MOVE StateCode(StateNum-IO) TO StateCode-IO
MOVE StateName(StateNum-IO) TO StateName-IO
MOVE StateCapital(StateNum-IO) TO StateCapital-IO
MOVE StatePop(StateNum-IO) TO StatePop-IO
END-IF.
SearchUsingStateCode.
SEARCH State
AT END SET NoSuchStateCode TO TRUE
WHEN FUNCTION UPPER-CASE(StateCode(StateIdx)) EQUAL TO
FUNCTION UPPER-CASE(StateCode-IO)
SET StateNum-IO TO StateIdx
MOVE StateCode(StateIdx) TO StateCode-IO
MOVE StateName(StateIdx) TO StateName-IO
MOVE StateCapital(StateIdx) TO StateCapital-IO
MOVE StatePop(StateIdx) TO StatePop-IO
END-SEARCH.
SearchUsingStateName.
SEARCH State
AT END SET NoSuchStateName TO TRUE
WHEN FUNCTION UPPER-CASE(StateName(StateIdx)) EQUAL TO
FUNCTION UPPER-CASE(StateName-IO)
SET StateNum-IO TO StateIdx
MOVE StateCode(StateIdx) TO StateCode-IO
MOVE StateName(StateIdx) TO StateName-IO
MOVE StateCapital(StateIdx) TO StateCapital-IO
MOVE StatePop(StateIdx) TO StatePop-IO
END-SEARCH.
SearchUsingStateCapital.
SEARCH State
AT END SET NoSuchCapital TO TRUE
WHEN FUNCTION UPPER-CASE(StateCapital(StateIdx)) EQUAL TO
FUNCTION UPPER-CASE(StateCapital-IO)
SET StateNum-IO TO StateIdx
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Chapter 16 ■ Creating Large SyStemS
MOVE StateCode(StateIdx) TO StateCode-IO
MOVE StateName(StateIdx) TO StateName-IO
MOVE StateCapital(StateIdx) TO StateCapital-IO
MOVE StatePop(StateIdx) TO StatePop-IO
END-SEARCH.
This program takes as parameters StateNum-IO, StateCode-IO, StateName-IO, StateCapital-IO, StatePop-IO,
and ErrorFlag. Whichever of the first four parameters has a value is used as the search term to find the other information about the state. For instance, if StateName-IO has a value, then that is used as the search term to find the state number, state code, state capital, and state population.
If an error condition is detected, such as none of the fields having a value, then the appropriate error condition is set; this results in an error code being returned in the ErrorFlag parameter. If ErrorFlag contains zero, then no error was detected. The errors detected are given by the following condition names:
88 NoErrorFound VALUE ZERO.
88 InvalidStateNum VALUE 1.
88 NoSearchItems VALUE 2.
88 NoSuchStateCode VALUE 3.
88 NoSuchStateName VALUE 4.
88 NoSuchCapital VALUE 5.
The State Knowledge Game
Listing 16-5 is a game to test your knowledge of the names, codes, capitals, and populations of American states. It uses the GetStateInfo external subprogram.
Listing 16-5. A Game to Test Your Knowledge of American States
IDENTIFICATION DIVISION.
PROGRAM-ID. Listing16-5.
AUTHOR. Michael Coughlan.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 Parameters.
02 StateNum PIC 99.
02 StateCode PIC XX.
02 StateName PIC X(14).
02 StateCapital PIC X(14).
02 StatePop PIC 9(8).
02 ErrorFlag PIC 9.
01 idx PIC 99.
01 CurrentTime.
02 FILLER PIC 9(4).
02 Seed PIC 9(4).
01 RandState PIC 99.
01 RandChoice PIC 9.
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Chapter 16 ■ Creating Large SyStemS
01 Answer PIC X(14).
01 PopAnswer PIC 9(8).
01 MinPop PIC 9(8).
01 MaxPop PIC 9(8).
01 PrnStatePop PIC ZZ,ZZZ,ZZ9.
01 StrLength PIC 99.
PROCEDURE DIVISION.
Begin.
ACCEPT CurrentTime FROM TIME
COMPUTE RandState = FUNCTION RANDOM(Seed)
PERFORM 8 TIMES
COMPUTE RandState = (FUNCTION RANDOM * 50) + 1
COMPUTE RandChoice = (FUNCTION RANDOM * 4) + 1
CALL "GetStateInfo"
USING BY REFERENCE RandState, StateCode, StateName,
StateCapital, StatePop, ErrorFlag
EVALUATE RandChoice
WHEN 1 PERFORM TestCapitalFromState
WHEN 2 PERFORM TestCodeFromState
WHEN 3 PERFORM TestPopFromState
WHEN 4 PERFORM TestStateFromCapital
END-EVALUATE
DISPLAY SPACES
END-PERFORM
STOP RUN.
TestCapitalFromState.
CALL "GetStringLength" USING BY CONTENT StateName
BY REFERENCE StrLength
DISPLAY "What is the capital of " StateName(1:StrLength) "? "
WITH NO ADVANCING
ACCEPT Answer
IF FUNCTION UPPER-CASE(Answer) = FUNCTION UPPER-CASE(StateCapital)
DISPLAY "That is correct"
ELSE
DISPLAY "That is incorrect. The capital of " StateName(1:StrLength)
" is " StateCapital
END-IF.
TestCodeFromState.
CALL "GetStringLength" USING BY CONTENT StateName
BY REFERENCE StrLength
DISPLAY "What is the state code for " StateName(1:StrLength) "? "
WITH NO ADVANCING
ACCEPT Answer
IF FUNCTION UPPE
R-CASE(Answer) = FUNCTION UPPER-CASE(StateCode)
DISPLAY "That is correct"
ELSE
DISPLAY "That is incorrect. The code for " StateName(1:StrLength)
" is " StateCode
END-IF.
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Chapter 16 ■ Creating Large SyStemS
TestPopFromState.
CALL "GetStringLength" USING BY CONTENT StateName
BY REFERENCE StrLength
DISPLAY "What is the population of " StateName(1:StrLength) "? "
WITH NO ADVANCING
ACCEPT PopAnswer
COMPUTE MinPop = PopAnswer - (PopAnswer * 0.25)
COMPUTE MaxPop = PopAnswer + (PopAnswer * 0.25)
MOVE StatePop TO PrnStatePop
IF StatePop > MinPop AND < MaxPop
DISPLAY "That answer is close enough. The actual population is " PrnStatePop
ELSE
DISPLAY "That is incorrect. The population of " StateName(1:StrLength)
" is " PrnStatePop
END-IF.
TestStateFromCapital.
CALL "GetStringLength" USING BY CONTENT StateCapital
BY REFERENCE StrLength
DISPLAY "Of what state is " StateCapital(1:StrLength) " the capital? "
WITH NO ADVANCING
ACCEPT Answer
IF FUNCTION UPPER-CASE(Answer) = FUNCTION UPPER-CASE(StateName)
DISPLAY "That is correct"
ELSE
DISPLAY "That is incorrect. The state for " StateCapital(1:StrLength)
" is " StateName
END-IF.
IDENTIFICATION DIVISION.
PROGRAM-ID. GetStringLength IS INITIAL.
AUTHOR. Michael Coughlan.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 CharCount PIC 99 VALUE ZEROS.
LINKAGE SECTION.
01 StringParam PIC X(14).
01 StringLength PIC 99.
PROCEDURE DIVISION USING StringParam, StringLength.
Begin.
INSPECT FUNCTION REVERSE(StringParam) TALLYING CharCount
FOR LEADING SPACES
COMPUTE StringLength = 14 - CharCount
EXIT PROGRAM.
END PROGRAM GetStringLength.
END PROGRAM Listing16-5.
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Chapter 16 ■ Creating Large SyStemS
This program contains a number of interesting features. First, it uses the RANDOM intrinsic function. The first time RANDOM is invoked, it generates a sequence of pseudo-random numbers using the current time as a seed. Subsequent uses of RANDOM return instances of those numbers.
The program gets two random numbers: one to choose which state to ask about and the other to choose what
kind of question to ask. Once the program has chosen the number of the state to ask about, it uses the CALL verb to get all the other information about the state. Depending on what question is asked, the program gets an answer from the user and then compares it with state information returned by the CALL.
Although most answers must be exact, conversion to uppercase is done so the letter case of the answer is not an issue. And because you can’t expect users to know the exact population of a state, any answer within 25 percent (higher or lower) of the actual value is accepted as correct.
An interesting problem is caused by displaying state names and capitals when the text does not fill the data item.
In that case, the data item is space filled, which causes unsightly output when the text is be displayed. For instance, a question about the capital of Delaware might display as follows:
: Of what state is Dover the capital?
To solve this issue, reference modification is used to slice out the actual text. To enable this slicing, the program calculates the length of the text. Because this operation is performed a number of times, it is removed to the contained subprogram GetStringLength.
Getting State Information
Listing 16-6 also uses the subprogram GetStateInfo, but in a more straightforward way. When the user provides a piece of information, such as a state name, the program displays all the other information about the state. The state number and the state code are two of the items displayed and you might think that having both of these items in the table is redundant. However, the importance of the state code is obvious and when I wrote the game in Listing 16-5
the state number proved useful because it made it easy to select the state at random. One other advantage of the state number is that you can use it to dump out all the values in the table (see Example 16-5).
Example 16-5. Fragment Showing How to Display the State Table Values
PERFORM VARYING idx FROM 1 BY 1 UNTIL idx > 50
MOVE idx TO StateNum
CALL "GetStateInfo"
USING BY REFERENCE StateNum, StateCode, StateName,
StateCapital, StatePop, ErrorFlag
DISPLAY StateNum ". " StateCode SPACE StateName
SPACE StateCapital SPACE StatePop
END-PERFORM
Listing 16-6. Using the GetStateInfo Subprogram as Intended
IDENTIFICATION DIVISION.
PROGRAM-ID. Listing16-6.
AUTHOR. Michael Coughlan.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 Parameters.
02 StateNum PIC 99.
02 StateCode PIC XX.
02 StateName PIC X(14).
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Chapter 16 ■ Creating Large SyStemS
02 StateCapital PIC X(14).
02 StatePop PIC 9(8).
02 ErrorFlag PIC 9.
88 NoError VALUE ZERO.
01 CurrentTime.
02 FILLER PIC 9(4).
02 Seed PIC 9(4).
01 RandChoice PIC 9.
01 PrnStatePop PIC ZZ,ZZZ,ZZ9.
PROCEDURE DIVISION.
Begin.
ACCEPT CurrentTime FROM TIME
COMPUTE RandChoice = FUNCTION RANDOM(Seed)
PERFORM 8 TIMES
DISPLAY SPACES
INITIALIZE Parameters
COMPUTE RandChoice = (FUNCTION RANDOM * 4) + 1
EVALUATE RandChoice
WHEN 1 DISPLAY "Enter a state number - " WITH NO ADVANCING
ACCEPT StateNum
WHEN 2 DISPLAY "Enter a two letter code - " WITH NO ADVANCING
ACCEPT StateCode
WHEN 3 DISPLAY "Enter a state name - " WITH NO ADVANCING
ACCEPT StateName
WHEN 4 DISPLAY "Enter a state capital - " WITH NO ADVANCING
ACCEPT StateCapital
END-EVALUATE
CALL "GetStateInfo"
USING BY REFERENCE StateNum, StateCode, StateName,
StateCapital, StatePop, ErrorFlag
IF NoError
MOVE StatePop TO PrnStatePop
DISPLAY StateNum ". " StateCode SPACE StateName
SPACE StateCapital SPACE PrnStatePop
ELSE
DISPLAY "There was an error. Error Code = " ErrorFlag
END-IF
END-PERFORM
STOP RUN.
In this program the search term type is chosen at random, the user is asked to supply a value for it, and then GetStateInfo is called to return the appropriate values for that search term.
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Chapter 16 ■ Creating Large SyStemS
The IS EXTERNAL Clause
The IS GLOBAL clause allows a program and its contained subprograms to share access to a data item. The IS EXTERNAL
clause does the same for any subprogram in a run-unit (that is, any linked subprogram), but it has restrictions that make it much more cumbersome to use than the IS GLOBAL phrase. Whereas a data item that uses the IS GLOBAL phrase only has to be declared in one place, each of the subprograms that wish to access an EXTERNAL shared item must declare the item—and it must be declared exactly the same way in each subprogram. Figure 16-7 illustrates the IS EXTERNAL
data-sharing mechanism.
Figure 16-7.
The IS EXTERNAL data-sharing mechanism
Figure 16-7 shows the calling structure of a run-unit that consists of four linked programs: a main program (ProgramA) and three subprograms. In the illustration, ProgramB and ProgramD share data using the IS EXTERNAL
mechanism. In order to share the data, both subprograms must declare the data, and the declarations have to be exactly the same. That is, they must each have the following declaration:
01 SharedRec IS EXTERNAL.
02 Stock-Id PIC 9(7).
02 Manf-Id PIC X(5).
In this system, ProgramB communicates with ProgramD by passing it data through the shared data item
SharedRec. This might work as follows: ProgramA does some work and then calls ProgramB, which moves a value into SharedRec as part of its work. When control returns to ProgramA, it does some more work, calls ProgramC to do some work, and then calls ProgramD. ProgramD then uses the data from the shared area SharedRec to perform its task.
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Chapter 16 ■ Creating Large SyStemS
IS EXTERNAL Problems
The problem with using the IS EXTERNAL phrase is that the transfer of data between ProgramB and ProgramD is detectable only by inspecting B and D. Even though ProgramA invokes B and D, a programmer inspecting A will not realize that B and D are secretly communicating. Even worse, at some point in the future, a maintenance programmer may decide that ProgramC needs to communicate with ProgramD using the shared area and may overwrite the data placed there by ProgramB.
The kind of hidden data communication between subprograms that you see when you use the IS EXTERNAL
clause is generally regarded as very poor practice. According to the measures of module goodness discussed by Myers1 common coupling is almost the worst kind of data connection you can have between modules. Subprograms that use the IS EXTERNAL clause to create shared data items are common coupled. Common-coupled modules exhibit a number of problems, such as naming dependencies, creation of dummy structures, and exposure to unnecessary data. Most of these issues are caused by the requirement that each subprogram that wants to use the shared area must describe it exactly the same way.
To illustrate the problem, consider the following scenario. A programmer creates a module to do check digit validation for the Stock-Id. Instead of using the parameter list to get the number to be validated, the programmer takes advantage of the fact that the Stock-Id is an EXTERNAL shared data item and gets access to the Stock-Id using this shared area. The first problem the programmer has is to make sure that their module is not overwriting the data moved into the shared area by some other subprogram. The second problem the programmer has is that their module has to describe the shared area as follows:
Michael Coughlan Page 51
