How write a PL/SQL program that prints out string which looking like xml format - oracle

Question

Input String : “a4b4c2d9d9c2e6e6b4s2o1o1s2a4w2r8r8k3g5g5k3w2”
I tried this code as first step:
declare
word varchar2(50) := 'a4b4c2d9d9c2e6e6b4s2o1o1s2a4w2r8r8k2g5g5k2w2';
num number := length(word)/2;
name_array dbms_sql.varchar2_table;
begin
dbms_output.put_line(word);
FOR i IN 1..num LOOP
name_array(i) := substr(word, -2*i, 2);
END LOOP;
FOR i IN name_array.FIRST .. name_array.LAST LOOP
dbms_output.put_line(name_array(i));
END LOOP;
end;
This code creates only an array of string. Not xml format. I need this output:
Which SQL functions,conditional clauses... do I need to use?

Answer 1

Oracle Setup:
CREATE OR REPLACE TYPE CHARS_TABLE IS TABLE OF CHAR(2);
/
CREATE OR REPLACE TYPE INTEGERS_TABLE IS TABLE OF INTEGER;
/
PL/SQL:
This assumes a well-formed set of character pairs and just indents each pair to the appropriate level:
DECLARE
word VARCHAR2(50) := 'a4b4c2d9d9c2e6e6b4s2o1o1s2a4w2r8r8k2g5g5k2w2';
num PLS_INTEGER := LENGTH( word ) / 2;
name_array CHARS_TABLE := CHARS_TABLE();
depth_array INTEGERS_TABLE := INTEGERS_TABLE();
open_array INTEGERS_TABLE := INTEGERS_TABLE();
BEGIN
name_array.EXTEND( num );
depth_array.EXTEND( num );
open_array.EXTEND( num );
name_array(1) := SUBSTR( word, 1, 2 );
depth_array(1) := 1;
open_array(1) := 1;
FOR i IN 2 .. num LOOP
name_array(i) := SUBSTR( word, 2*i - 1, 2 );
open_array(i) := 1;
FOR j IN 1 .. i-1 LOOP
IF name_array(j) = name_array(i) THEN
open_array(i) := -open_array(i);
END IF;
END LOOP;
depth_array(i) := depth_array(i-1) + open_array(i);
END LOOP;
FOR i IN 1 .. num LOOP
FOR j IN 2 .. depth_array(i) + CASE open_array(i) WHEN 1 THEN 0 ELSE 1 END LOOP
DBMS_OUTPUT.PUT( ' ' );
END LOOP;
DBMS_OUTPUT.PUT_LINE( name_array(i) );
END LOOP;
END;
/
Output:
a4
b4
c2
d9
d9
c2
e6
e6
b4
s2
o1
o1
s2
a4
w2
r8
r8
k2
g5
g5
k2
w2
Update - Simpler Stack-Based Version:
DECLARE
word CONSTANT VARCHAR2(50) := 'a4b4c2d9d9c2e6e6b4s2o1o1s2a4w2r8r8k2g5g5k2w2';
num CONSTANT PLS_INTEGER := LENGTH( word ) / 2;
name_array CHARS_TABLE := CHARS_TABLE();
depth PLS_INTEGER := 0;
name CHAR(2);
PROCEDURE indent( depth PLS_INTEGER, name CHAR )
IS
BEGIN
FOR j IN 2 .. depth LOOP
DBMS_OUTPUT.PUT( ' ' );
END LOOP;
DBMS_OUTPUT.PUT_LINE( name );
END;
BEGIN
name_array.EXTEND( num );
FOR i IN 1 .. num LOOP
name := SUBSTR( word, 2*i - 1, 2 );
IF depth > 0 AND name = name_array(depth) THEN
indent(depth,name);
depth := depth - 1;
ELSE
depth := depth - 1;
name_array(depth) := name;
indent(depth,name);
END IF;
END LOOP;
END;
/

Answer 2

DECLARE
vs_CurrentChar VARCHAR2(1);
vs_NextChar VARCHAR2(1);
vs_TempText VARCHAR2(100);
vs_InputText VARCHAR2(100) := 'abcdffdcba';
vn_LengthOfText NUMBER := 1;
vn_WhileIndex NUMBER := 1;
vs_Spaces VARCHAR(100);
BEGIN
vs_TempText := NULL;
vs_CurrentChar := substr(vs_InputText, vn_WhileIndex, vn_LengthOfText);
dbms_output.put_line(vs_CurrentChar);
WHILE vn_WhileIndex < length(vs_InputText) - 1 LOOP
vs_NextChar := substr(vs_InputText, vn_WhileIndex + 1, vn_LengthOfText);
EXIT WHEN vs_CurrentChar = vs_NextChar;
vs_TempText := vs_TempText || vs_CurrentChar;
vs_CurrentChar := vs_NextChar;
vs_Spaces := NULL;
FOR i IN 1 .. vn_WhileIndex LOOP
vs_Spaces := vs_Spaces || chr(9); --'*';
END LOOP;
dbms_output.put_line(vs_Spaces || vs_CurrentChar);
vn_WhileIndex := vn_WhileIndex + 1;
END LOOP;
dbms_output.put_line(vs_Spaces || vs_CurrentChar);
FOR i IN 1 .. length(vs_TempText) LOOP
vs_Spaces := substr(vs_Spaces, vn_LengthOfText, length(vs_Spaces) - 1);
vs_CurrentChar := substr(vs_TempText, -i, vn_LengthOfText);
dbms_output.put_line(vs_Spaces || vs_CurrentChar);
END LOOP;
END;
/
And output:
a
b
c
d
f
f
d
c
b
a
even, if you put '*'; instead of chr(9); then output will look like as:
a
*b
**c
***d
****f
****f
***d
**c
*b
a