declare
type t1 is table of varchar2(20)
index by binary_integer;
vt t1;
   cursor c1 is select last_name from employees;
   i=i+1;
  begin
for i in c1 loop  

   i:=i+1;
 end loop;
  for i in vt.first..vt.last
    loop
     dbms_output.put_line(vt(i));
   end loop;
 end;

ERROR at line 6:
ORA-06550: line 6, column 5:
PLS-00103: Encountered the symbol "=" when expecting one of the following:

declare
type t1 is table of varchar2(20)
index by binary_integer;
vt t1;
   cursor c1 is select last_name from employees;
  begin
for i in c1 loop  
   i:=i+1;
 end loop;
  for i in vt.first..vt.last
    loop
     dbms_output.put_line(vt(i));
   end loop;
 end;

SCOTT@orcl> declare
  2    type t1 is table of varchar2(20) index by binary_integer;
  3    vt t1;
  4    cursor c1 is select last_name from employees;
  5    -- declare your variable i and initialize the value:
  6    i number := 0;
  7  begin
  8    -- use something different (like r1) instead of i for your
  9    -- record identifier to avoid conflicts:
 10    for r1 in c1 loop
 11  	 -- increment the variable i by 1 each time through the loop:
 12  	 i := i + 1;
 13  	 -- set the value of the ith record of the vt associative array
 14  	 -- using the last_name of the record (r1) of the cursor c1:
 15  	 vt(i) := r1.last_name;
 16    end loop;
 17    for i in 1 .. vt.count loop
 18  	 dbms_output.put_line(vt(i));
 19    end loop;
 20  end;
 21  /
SMITH
ALLEN
WARD
JONES
MARTIN
BLAKE
CLARK
SCOTT
KING
TURNER
ADAMS
JAMES
FORD
MILLER

PL/SQL procedure successfully completed.

declare
    type t1 is table of employees.last_name%TYPE index by binary_integer;
    vt t1;
  begin

    select last_name  BULK COLLECT INTO vt from employees;

    for i in 1 .. vt.count loop
     dbms_output.put_line(vt(i));
    end loop;
  end;
/