uses crt;
var s:string; i,hoa,thuong,so,db:longint;
begin
clrscr;
   write('Nhap mat khau: ');readln(s);
   for i:=1 to length(s) do
      begin
         if s[i] in ['A'..'Z'] then inc(hoa) else
         if s[i] in ['a'..'z'] then inc(thuong) else
         if s[i] in ['0'..'9'] then inc(so) else inc(db);
      end;
   writeln((hoa>0)and(thuong>0)and(so>0)and(db>0));
readln
end.

Mình sẽ xác định là các kí tự khác ngoài a → z; A→Z; 0→9

Code

Program mkmanh;
var pass:string;
a: boolean;
s,t,h,k,i:longint;
BEGIN
Readln(pass);
s:=0; t:=0; h:=0; k:=0;
For i := 1 to length(pass) do
begin
If pass[i] in ['0'..'9'] then s:=s+1;
If pass[i] in ['a'..'z'] then t:=t+1;
If pass[i] in ['A'..'Z'] then h:=h+1;
If not(pass[i] in ['a'..'z','A'..'Z','0'..'9']) then k:=k+1;
end;
If (s>0) and (t>0) and (h>0) and (k>0) then a:= true else a:=false;
Write(a);
Readln;
END.