Oracle Stored Procedure compilation error - oracle

Question

I'm new to PL/SQL. Can anyone please help fix my compilation error? Your help is much appreciated. Also, after I would like to call this procedure to check and add a new user.
create or replace procedure CheckAddUser ( userid in varchar2(20))
as
declare vartmp number;
begin
SELECT nvl((SELECT distinct 1 FROM crm_admin.LTY_USER_STORE WHERE usr_nm = userid ), 0) INTO :varTmp FROM dual;
IF (:varTmp = 0) THEN
dbms_output.put_line('the user ' || ':userid' || ' does not exist');
elsif (:varTmp = 1) THEN
dbms_output.put_line('the user ' || ':userid' || ' already exist');
End if;
end;

Answer 1

Try this:
create or replace procedure checkadduser(userid in varchar2)
as
vartmp number;
begin
select coalesce(max(1), 0) into vartmp
from dual
where exists (
select 1
from crm_admin.lty_user_store
where usr_nm = userid
);
if vartmp = 0 then
dbms_output.put_line('the user ' || userid || ' does not exist');
elsif vartmp = 1 then
dbms_output.put_line('the user ' || userid || ' already exist');
end if;
end;
/
Changes made:
Removed the size from parameter
Removed the declare keyword - not part of the procedure syntax
Modified the query to stop searching as soon as a row is found and return 1 otherwise 0.
select coalesce(max(1), 0) into varTmp
from dual
where exists (
select 1
from crm_admin.lty_user_store
where usr_nm = userid
);
If the usr_nm is unique in your table, this will work well too (this can be used even if it's not unique but can be bit less performant if number of rows per usr_nm can be arbitrarily large):
select coalesce(max(1), 0)
into varTmp
from crm_admin.lty_user_store
where usr_nm = userid
Do not use : with the variables and parameters.

Answer 2

Don't use ":" with var.
I did some changes, which I would migth use:
--I recommended to change procedure to function, then you can use it in SQL
create or replace
procedure CheckAddUser ( userid in varchar2)
as
--Best practics, use self-describing variables
isuserexist number(1,0); -- vartmp
message_suff varchar2(30):=' does not exist';
begin
--Best practics, first check the parameters
if trim(userid) is null then
raise_application_error(-20000, 'Param userid is empty');
end if;
select count(*) into isuserexist
from crm_admin.lty_user_store
where usr_nm = userid;
--only one if, reads easier
if isUserExist > 0 then
message_suff:= ' already exist';
end if;
dbms_output.put_line('the user ' || ':userid' || message_suff);
end;