*An internal table is a run time instance.  It get created when program starts execution.
*It get destroyed when program terminates. it has two different parts.  HeaderLine(optional) & Body(Compulsory).
*Any value that comes to or goes from interanal table , that travels through headerline.\

*A related program is .

*declaration.
data: begin of inernaltable occurs 0,
         x type c,
         y type i,
      end of itab.

*initializing headerline
   internaltable-x = 'd'.
   internaltable-y = 34.

*storing value into internal table

appene internaltable . 
appene internaltable .
appene internaltable .

*reading internal table
loop at itab .
   write: / internaltable-x, internaltable-y.  "writes to output list
endloop.

ABAP Tips by : Abdul Sayeed
Email : sayeed_mail2005@yahoo.com

Fields of Internal Tables

SY-TABIX

Current line of an internal table. SY-TABIX is set by the statements below, but only for index tables. The field is either not set or is set to 0 for hashed tables. 

APPEND sets SY-TABIX to the index of the last line of the table, that is, it contains the overall number of entries in the table. 

COLLECT sets SY-TABIX to the index of the existing or inserted line in the table. If the table has the type HASHED TABLE, SY-TABIX is set to 0.

LOOP AT sets SY-TABIX to the index of the current line at the beginning of each loop lass. At the end of the loop, SY-TABIX is reset to the value that it had before entering the loop. It is set to 0 if the table has the type HASHED TABLE. 

READ TABLE sets SY-TABIX to the index of the table line read. If you use a binary search, and the system does not find a line, SY-TABIX contains the total number of lines, or one more than the total number of lines. SY-INDEX is undefined if a linear search fails to return an entry. 

SEARCH <itab> FOR sets SY-TABIX to the index of the table line in which the search string is found.

SY-TFILL

After the statements DESCRIBE TABLE, LOOP AT, and READ TABLE, SY-TFILL contains the number of lines in the relevant internal table. 

SY-TLENG

After the statements DESCRIBE TABLE, LOOP AT, and READ TABLE, SY-TLENG contains the length of the lines in the relevant internal table. 

SY-TOCCU

After the statements DESCRIBE TABLE, LOOP AT, and READ TABLE, SY-TLENG contains the initial amount of memory allocated to the relevant internal table.

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