why it isn't work? It's said main.pas(12,1) Fatal: Syntax error, "BEGIN" expected but "identifier D" found

Question

program Hello;
uses crt;
d,i,vt,dem:integer;
begin
clrscr;
write('nhap xau S:'); readln(s);
d:=length(s);
st:="";
for i:=1 to d do
if s[i] in ['0'..'9'] then st:=st+s[i];
writeln('Xau moi vua duoc tao la: ',st);
for i:=1 to d do
if (s[i]<>'a') and (s[i]<>'b') then write(s[i]);
writeln;
st1:='tin';
vt:=pos(st1,s);
if vt=0 then writeln(s)
else
begin
inc(dem);
a[dem]:=vt;
end;
if dem>0 then
begin
for i:=1 to dem do
begin
delete(s,a[i],3);
insert('pascal',s,a[i]);
end;
writeln;
end;
readln;
end.

Answer 1

use var beffor  variables :
 

var

d,i,vt,dem:integer;

Answer 2

and you must make s and str in variables:

s,st:string[255];

also

you cant make

st="" in pascal it's forbiden

Answer 3

Variable declarations in pascal need a var keyword.