SQL> declare p number:=0; begin
  2   for k in 1 .. 10 loop  DBMS_OUTPUT.PUT_LINE( '5 *' ||k ||'='||5*k); end loop;
  3  end;
  4  /
PL/SQL procedure successfully completed.

SQL> set serverout on;
SQL> /
5 *1=5
5 *2=10
5 *3=15
5 *4=20
5 *5=25
5 *6=30
5 *7=35
5 *8=40
5 *9=45
5 *10=50

PL/SQL procedure successfully completed.

SQL> declare a varchar2(100); b number; 
begin a:='&a'; for i in 1 .. length(a) loop 
dbms_output.put_line(substr(a,i,1)); end loop; end;
  2  /
Enter value for a: Hello
old   1: declare a varchar2(100); b number; begin a:='&a'; .
for i in 1 .. length(a) loop dbms_output.put_line(substr(a,i,1)); end loop; end;
new   1: declare a varchar2(100); b number; 
begin a:='Hello'; for i in 1 .. length(a) loop
 dbms_output.put_line(substr(a,i,1)); end loop; end;

H
e
l
l
o

PL/SQL procedure successfully completed