Logical Expressions - Is a Field Symbol Assigned?

<fs> IS [NOT] ASSIGNED queries, whether the field symbol <fs> is assigned a field (ASSIGN).

Example

FIELD-SYMBOLS <FS> TYPE ANY.
IF <FS> IS NOT ASSIGNED.
  WRITE 'That is O' NO-GAP.
ENDIF.
ASSIGN SY-SUBRC TO <FS>.
IF <FS> IS ASSIGNED.
  WRITE 'K.'.
ENDIF.

Output: That is OK.

Additional help

Checking Whether a FieldSymbol is Assigned