function RandomStr(majuscule:boolean;lowercase:boolean;number:boolean;digit:integer):string;
//大写字母,小写字母,数字,字符串的位数
var
i: Byte;
s: string;
begin
if majuscule then
s := 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
else
s := '';

if lowercase then
s := s + 'abcdefghijklmnopqrstuvwxyz';

if number then
s := s + '0123456789';
if s = '' then exit;

Result := '';
for i := 0 to digit-1 do //根据长度来循环
begin
Randomize;//每次都初始化随机种子
Result := Result + s[Random(Length(s)-1)+1];
end;
end;