Sample plsql code- for practice

This is sample  code 1:

declare
  test_message varchar2(30):='Hello World';
  message varchar2(20);
 begin
 message:='This is Arvind';
 DBMS_OUTPUT.PUT_LINE(test_message || ' ' || message);
 END;
 /

This is sample  code 2:


 declare
  num1 number:='10';
  num2 number:='3';
  num number;
  num3 number;
 begin
  num:= num1+ num2;
  DBMS_OUTPUT.PUT_LINE('This is num1: '||num1  || ', This is num2: ' || num2);
  DBMS_OUTPUT.PUT_LINE('This is the ouput num1+num2: ' || num);
 num3:=num+37;
 DBMS_OUTPUT.PUT_LINE('This is the ouput num3: ' || num3);
 END;
 /


Sample code 3:

declare
A1 number := &A1;
B1 number := &B1;
C1 number;
ERR exception;
begin

C1 :=A1 + B1;
if C1 <= 5 then
raise ERR;
else
DBMS_OUTPUT.PUT_LINE (' Value of C1 is '||C1||'' );
end if;
EXCEPTION
  WHEN ERR THEN
 DBMS_OUTPUT.PUT_LINE (' Value of C1 is less than 5' );
 end;