【php】随机验证码的生成

<?php

function randMima  ($num = 6) {
$ychar="0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z";
$list=explode(",",$ychar);
$authnum = '';
for($i=0;$i<$num;$i++){
$randnum=rand(0,61);
$authnum.=$list[$randnum];
}
return $authnum;
}
echo randMima (8);

?>