DECLARE
  Dummy_Define CHAR(1);

  CURSOR SYSTEM_VARIABLES_cur IS      
    SELECT 1 FROM SYS_VARS S     
    WHERE S.VAR_NAME = :PP.PPI;

BEGIN
   
  OPEN SYSTEM_VARIABLES_cur;        
  FETCH SYSTEM_VARIABLES_cur INTO Dummy_Define;  
  IF ( SYSTEM_VARIABLES_cur%found ) THEN     
    Message('Error ...');     
    CLOSE SYSTEM_VARIABLES_cur;     
    RAISE Form_Trigger_Failure;     
  END IF;
  CLOSE SYSTEM_VARIABLES_cur;
 
END;

SELECT 1                     --> 1 is a NUMBER
INTO Dummy_Define            --> you defined this variable as CHAR(1)
FROM SYS_VARS S
WHERE ...