I cannot Disable a constraint in SQL Developer

Question

Here is my issue:
I have created a table already named practice1.
Using SQL Developer PL/SQL try to run a loop as following:
DECLARE
COUNTER1  NUMBER(2);
BEGIN
COUNTER1 := 30;
ALTER TABLE practice1
DISABLE  CONSTRAINT PRK1;
LOOP
COUNTER1 := 30;
INSERT INTO PRACTICE1
VALUES (COUNTER1, 'test7', 8, 9);
EXIT WHEN  COUNTER1 >26;
END LOOP;
END;
In other words I Insert the COUNTER1 variable value as Primary Key in the tables field1 column.
I run the script successfully without the ALTER TABLE DISABLE CONTSRAINT.. command.
Everytime I run it I had to increase the starting value of Variable COUNTER1 so it will not attempt to insert a duplicate pre-existed value in Primary Key.
Then I decided to insert the command ALTER TABLE DISABLE CONSTRAINT in order to not have to worry to change the starting value.
I am able to disable the constraint by using the same command in isolation . If I run it as part of the script as above I get the following error:
Error report:
ORA-06550: line 5, column 1:
PLS-00103: Encountered the symbol "ALTER" when expecting one of the following:
   ( begin case declare end exception exit for goto if loop mod
   null pragma raise return select update while with
   <an identifier> <a double-quoted delimited-identifier>
   <a bind variable> << continue close current delete fetch lock
   insert open rollback savepoint set sql execute commit forall
   merge pipe purge
06550. 00000 -  "line %s, column %s:\n%s"
*Cause:    Usually a PL/SQL compilation error.
*Action:
I would appreciate any suggestions.
Thank you.

Answer 1

Your question has NOTHING to do with sql developer.
Mark this question ANSWERED and repost it in the SQL and PL/SQL forum.
https://forums.oracle.com/community/developer/english/oracle_database/sql_and_pl_sql
The problem is that you CANNOT execute DDL directly in PL/SQL. You need to use dynamic SQL to execute DDL within PL/SQL.
EXECUTE IMMEDIATE 'ALTER TABLE . . .';
If you need more help use the correct forum as shown above.