SCOPE OF VARIABLE in PL/SQL

--1st Scenario
SET SERVEROUTPUT ON
DECLARE
v_weight NUMBER(3):=600;
v_message VARCHAR2(255):=' Product 10012';
v_new_locn VARCHAR2(50) :='America';

BEGIN
        DECLARE
        v_weight  NUMBER(3) :=1;
        v_message VARCHAR2(255):='Product 11001';
        v_new_locn VARCHAR2(50) :='Europe';
        BEGIN
        v_weight :=v_weight+1;
        DBMS_OUTPUT.PUT_LINE(v_weight);
        DBMS_OUTPUT.PUT_LINE(v_message);
        v_new_locn:='Western  ' || v_new_locn;
        DBMS_OUTPUT.PUT_LINE(v_new_locn);
        END;      
v_weight := v_weight+1;
DBMS_OUTPUT.PUT_LINE(v_weight);
v_message:=v_message || ' is in stock';
DBMS_OUTPUT.PUT_LINE(v_message);
v_new_locn :='Eastern  '||v_new_locn;
DBMS_OUTPUT.PUT_LINE(v_new_locn);
END;


1st Output:

2
Product 11001
Western  Europe
601
Product 10012 is in stock
Eastern  America

*******************************xxxxxxxxxxxx****************************************

2nd Scenario:

-We can access a variable from outer block whether it is declared or not in the inner block but not vice versa.
--Inner Block executes once before the outer block.
--The scope of the variable ends within the BEGIN ... END statement of the inner block.

DECLARE
v_weight NUMBER(3):=600;
v_message VARCHAR2(255):=' Product 10012';
v_new_locn VARCHAR2(50) :='America';

BEGIN
        DECLARE
        v_message VARCHAR2(255):='Product 11001';
        v_new_locn VARCHAR2(50) :='Europe';
        --v_weight  NUMBER(3) :=1;
/*v_weight variable commented out in the inner block to see the difference by not declaring in inner
block but calling it from outer block */
BEGIN
        v_weight :=v_weight+1;   /* taking value from outer block and incremented */
        DBMS_OUTPUT.PUT_LINE(v_weight);
        DBMS_OUTPUT.PUT_LINE(v_message);      
        v_new_locn:='Western  ' || v_new_locn;
        DBMS_OUTPUT.PUT_LINE(v_new_locn);
        END;      
v_weight := v_weight+1;  /* taking value derived from inner block and further incremented as inner block executes once before outer block*/
DBMS_OUTPUT.PUT_LINE(v_weight);
v_message:=v_message || ' is in stock';
DBMS_OUTPUT.PUT_LINE(v_message);
v_new_locn :='Eastern  '||v_new_locn;
DBMS_OUTPUT.PUT_LINE(v_new_locn);
END;



2nd Output: 

601
Product 11001
Western  Europe
602
Product 10012 is in stock
Eastern  America

*********************************xxxxxx**********************************

--3rd  Scenario
DECLARE
v_weight NUMBER(3):=600;
v_message VARCHAR2(255):=' Product 10012';

BEGIN
        DECLARE
        v_weight  NUMBER(3) :=1;
        v_message VARCHAR2(255):='Product 11001';
        v_new_locn VARCHAR2(50) :='Europe';
        BEGIN
        v_weight :=v_weight+1;
        DBMS_OUTPUT.PUT_LINE(v_weight);
        DBMS_OUTPUT.PUT_LINE(v_message);
        
        v_new_locn:='Western  ' || v_new_locn;
        DBMS_OUTPUT.PUT_LINE(v_new_locn);
        END;        
v_weight := v_weight+1;
DBMS_OUTPUT.PUT_LINE(v_weight);
v_message:=v_message || ' is in stock';
DBMS_OUTPUT.PUT_LINE(v_message);
v_new_locn :='Eastern  '||v_new_locn; /* We can't call v_new_locn from inner block as it is not declared in outer block*/
/*v_new_locn is not visible in the main block and you would see an error*/  

DBMS_OUTPUT.PUT_LINE(v_new_locn);
END;

compilation error:

PLS-00201: identifier 'V_NEW_LOCN' must be declared
ORA-06550: line 23, column 1:
PL/SQL: Statement ignored 


Cheers
Rajani