All about Indicators:

RPG IV has the introduction of the following indicators:
• Named Indicators
• Logical Expressions
• Built-In Functions (BIFs)
• The Indicator Data Structure (INDDS)
That means the only RPG indicator we may have to use is *INLR!
Named Indicators
Indicators are now a recognized data type in RPG, so we can define them in the D Specs, as shown below. Note that when testing an indicator you do not need to compare it against *ON or *OFF.
DName+++++++++++ETDsFrom+++To/L+++IDc.Keywords+++++
D BadStatus S N
D MonthEnd S N
The below code shows a named indicator being used for printer overflow. This is a simple example of the benefit of a named indicator; the name Overflow is more self-explanatory than *IN96 or *INOV. Also, you don't need to define the Overflow indicator in the D Specs; the compiler will define it for you.
FReport O E Printer OflInd(OverFlow)

Write Detail;
If OverFlow;
Write Header;
OverFlow = *Off;
EndIf;

Logical Expressions
The result of a logical expression is true or false, therefore it can be assigned directly to an indicator.
If MonthEnd;
BadStatus = (Status <> 'I' and Status <> 'C');
EndIf;

Built In-Functions
We no longer need to use resulting indicators on operation codes. Instead, we can use the relevant I/O BIF. The I/O BIFs are %OPEN, %FOUND, %EOF, %ERROR, %EQUAL and %STATUS. The code below shows an example of using the %OPEN, %ERROR and %FOUND BIFs. The %OPEN BIF indicates whether or not the file is open. The %ERROR BIF is set when the E extender is defined on an operation code (Chain in this case). We use the E extender in place of an error indicator in the low position. The %FOUND BIF is set automatically by the Chain operation.
If %Open(FileB);
Chain(E) Key FileB;
Select;
When %Error;
Dsply 'File Error';
When %Found(FileB);
Dsply 'Got It';
EndIf;
EndIf;
One of the nice things about %FOUND is that it reads the right way round, as opposed to the indicator on the CHAIN operation where the indicator is true if the record is NOT found.
Indicator Data Structure
By default, the indicators 01 to 99 on a display or print file are mapped to the indicators 01 to 99 in an RPG program. But when we use the file keyword INDDS (Indicator Data Structure), they are mapped to a data structure instead of the indicators. In other words, the 99 indicators used with the display or print file are now associated with the data structure instead of the indicators *IN01 to *IN99 in the program.
The code below shows an example of using the INDDS. The indicators for the display file are mapped to the data structure DspInd. DspInd is a 99 byte data structure, with each byte corresponding to one of the 99 indicators for the display file. This means that for the display file, we MUST use the indicators in the data structure and NOT the numbered indicators. For example, in this program, if we turned on indicator *IN31, it would have no impact on the display file. The program logic must refer to the indicator Error in order to have an impact on the display file. Named indicators are a lot easier to decipher!
FDisplay CF E WORKSTN INDDS(DspInd)

D DspInd DS
* Response indicators
D F3Exit 3 3N
D F12Cancel 12 12N
* Conditioning indicators
D AllErrors 31 33
D Error 31 31N
D StDateErr 32 32N
D EndDateErr 33 33N

Eval AllErrors = *Zeros;

StDateErr = StartDate < Today;
EndDateErr = EndDate < StartDate;
Error = StDateErr or EndDateErr;

ExFmt MyScreen;

If F3Exit or F12Cancel;
The use of INDDS requires the use of the file level keyword INDARA in the DDS for the display/print file. In most cases, changing a file to use INDARA will have no effect unless a RESET or CLEAR operation is used. In this case it will now be necessary to also RESET/CLEAR the associated indicators.