php实现加减法验证码代码

class imagecode{

 private $jiashu  = 0;        //加数或者减数
 private $jianshu = 0;        //被加数或者被减数
 private $yunsuan = '';       //运算符
 private $deshu   = 0;        //得数
 private $string  = '';       //字符串样式
 private $img;                //图片对象
 private $width   = 100;      //图片宽度
 private $height  = 50;       //图片高度
 private $ttf     = 'num.ttf';//字体文件
 private $session = 'code';   //session变量

 private function jiashu(){
  header('content-type:image/png');
  $this -> jiashu  = rand(1, 10);
  $this -> jianshu = rand(1, 10);
  $this -> yunsuan= $this -> jiashu > $this -> jianshu ? '-' : '+';
  $this -> deshu   = $this -> jiashu > $this -> jianshu ? $this -> jiashu - $this -> jianshu : $this -> jiashu + $this -> jianshu;
 }

 public function show( $w = 100, $h = 50, $t = 'num.ttf', $code = 'code' ){
  $this -> jiashu();
  $this -> string = $this -> jiashu . $this -> yunsuan . $this -> jianshu . '= ? ';
  $this -> width  = $w;
  $this -> height = $h;
  $this -> ttf    = $t;
  $this -> session= $code;
  session_start();
  $_session[$this -> session] = $this -> deshu;
  $this -> images();
 }

 private function images(){
  $this -> img = imagecreate($this -> width, $this -> height);
  $background_color = imagecolorallocate ($this -> img, 255, 255, 255);
  imagecolortransparent($this -> img, $background_color);
        imagettftext($this -> img, 14, 0, 1, 20, imagecolorallocate ($this -> img, 0, 0, 0), $this -> ttf, $this -> string );
  $this -> echoimages();
 }

 private function echoimages(){
  imagepng($this -> img);
  imagedestroy($this -> img);
 }

}

$imagecode = new imagecode;
$imagecode -> show(130, 35, 'num.ttf', 'code');