:block.text_item := nvl(:block.text_item, 0) + 1;

SQL> select nvl(decode(&text_item, 100, 0, &text_item), 0) + 1 from dual;
Enter value for text_item: 99
Enter value for text_item: 99

NVL(DECODE(99,100,0,99),0)+1
----------------------------
                         100

SQL> /
Enter value for text_item: 100
Enter value for text_item: 100

NVL(DECODE(100,100,0,100),0)+1
------------------------------
                             1

SQL> /
Enter value for text_item: null
Enter value for text_item: null

NVL(DECODE(NULL,100,0,NULL),0)+1
--------------------------------
                               1

SQL> /
Enter value for text_item: 25
Enter value for text_item: 25

NVL(DECODE(25,100,0,25),0)+1
----------------------------
                          26

SQL>

l_decimal varchar2(50) default MOD( round(p_number,2), 1)*100;

SQL> WITH DATA AS
  2   (SELECT '150.20' A FROM DUAL),
  3  T(A,
  4  B,
  5  C) AS
  6   (SELECT A, TO_CHAR(TO_DATE(SUBSTR(A, 1, 1), 'J'), 'JSP') B, 1 AS C
  7      FROM DATA
  8    UNION ALL
  9    SELECT A,
 10           CASE
 11              WHEN SUBSTR(A, C + 1, 1) = '.' THEN
 12               'DOLLARS AND'
 13              WHEN SUBSTR(A, C + 1, 1) = '0' THEN
 14               'ZERO'
 15              ELSE
 16               TO_CHAR(TO_DATE(SUBSTR(A, C + 1, 1), 'J'), 'JSP')
 17           END B,
 18           C + 1 AS C
 19      FROM T
 20     WHERE C < LENGTH(A))
 21  SELECT LISTAGG (B, ' ') WITHIN GROUP (ORDER BY C) ||' '|| 'CENTS' AS "SPELLED" FROM T
 22  /
 
SPELLED
--------------------------------------------------------------------------------
ONE FIVE ZERO DOLLARS AND TWO ZERO CENTS