Editing ABAP (section)

==Types of ABAP programs==
As in other programming languages, an ABAP program is either an executable unit or a library, which provides reusable code to other programs and is not independently executable.

ABAP distinguishes two types of executable programs:

* Reports
* Module pools

Reports follow a relatively simple programming model whereby a user optionally enters a set of parameters (e.g., a selection over a subSET of data) and the program then uses the input parameters to produce a report in the form of an interactive list. The term "report" can be somewhat misleading in that reports can also be designed to ''modify'' data; the reason why these programs are called reports is the "list-oriented" nature of the output they produce.

Module pools define more complex patterns of user interaction using a collection of screens. The term “screen” refers to the actual, physical image that the user sees. Each screen also has a "flow logic", which refers to the ABAP code implicitly invoked by the screens, which is divided into a "PBO" (Process Before Output) and "PAI" (Process After Input) section. In SAP documentation the term “dynpro” (dynamic program) refers to the combination of the screen and its flow logic.

The non-executable program types are:

* '''INCLUDE modules''' – These get included at generation time into the calling unit; it is often used to subdivide large programs.
* '''Subroutine pools''' – These contain ABAP subroutines (blocks of code enclosed by FORM/ENDFORM statements and invoked with PERFORM).
* '''Function groups''' – These are libraries of self-contained function modules (enclosed by FUNCTION/ENDFUNCTION and invoked with CALL FUNCTION).
* '''Object classes''' – These are similar to Java classes and interfaces; the first define a set of methods and attributes, the second contain "empty" method definitions, for which any class implementing the interface must provide explicit code.
* '''Interfaces''' – Same as object classes
* '''Type pools''' – These define collections of data types and constants.

ABAP programs are composed of individual sentences (statements). The first word in a statement is called an ABAP keyword. Each statement ends with a period. Words must always be separated by at least one space. Statements can be indented as you wish. With keywords, additions and operands, the ABAP runtime system does not differentiate between upper and lowercase.

Statements can extend beyond one line. You can have several statements in a single line (though this is not recommended). Lines that begin with asterisk * in the first column are recognized as comment lines by the ABAP runtime system and are ignored. Double quotations marks (") indicate that the remainder of a line is a comment.