请教一问题啊

请教一问题啊

<?php
header("charset=utf8");
header("content-type: image/png");
$im=imagecreate(400,400);
$black=imagecolorallocate($im,0,0,0);
$white=imagecolorallocate($im,255,255,255);
$white1=imagecolorallocate($im,200,200,200);
$red=imagecolorallocate($im,100,40,40);
$red=imagecolorallocate($im,40,40,100);
for($px=-400;$px<400;$px=$px+20)
{
$x=$px/20;
imageline($im,0,$px+200,400,$px+200,$red);
imageline($im,$px+200,0,$px+200,400,$red);
}
for($px=0;$px<400;$px=$px+(20*M_PI))
{
$x=$px/20;
imageline($im,$px+200,0,$px+200,400,$red1);
imageline($im,0,$px+200,400,$px+200,$red1);
}
for($px=0;$px>-400;$px=$px-(20*M_PI));
{
$x=$px/20;
imageline($im,$px+200,0,$px+200,400,$red1);
imageline($im,0,$px+200,400,$px+200,$red1);

}
imageline($im,0,200,400,200,$white);
imageline($im,200,0,200,400,$white);
imageline($im,195,5.200,0,$white);
imageline($im,205,5,200,0,$white);
imageline($im,395,195,400,200,$white);
imageline($im,395,205,400,200,$white);
imagestring($im,10,385,200,"X",$white);
imagestring($im,10,185,0,"y",$white);
for($px=-400;$px<400;$px=$px+0.1)
{
$x=$px/20;
if($x!=0)
{
$y=sin($x);
}
$py=-$y*20;
imagesetpixel($im,$px+200,$px+200,$white);
}
imagepng($im,"wuliao");
imagedestroy($im);

?>
上面浏览以后出现这样一文件 ,怎么回事,请那位高手解答一下了谢谢



[复制到剪切板]
CODE:
<?php
//修正
header("charset=utf8");
header("content-type: image/png");
$im=imagecreate(400,400);
$black=imagecolorallocate($im,0,0,0);
$white=imagecolorallocate($im,255,255,255);
$white1=imagecolorallocate($im,200,200,200);
$red=imagecolorallocate($im,100,40,40);
$red=imagecolorallocate($im,40,40,100);
for(
$px=-400;$px<400;$px=$px+20)
{
$x=$px/20;
imageline($im,0,$px+200,400,$px+200,$red);
imageline($im,$px+200,0,$px+200,400,$red);
}
for(
$px=0;$px<400;$px=$px+(20*M_PI))
{
$x=$px/20;
imageline($im,$px+200,0,$px+200,400,$red1);
imageline($im,0,$px+200,400,$px+200,$red1);
}
for(
$px=0;$px>-400;$px=$px-(20*M_PI));
{
$x=$px/20;
imageline($im,$px+200,0,$px+200,400,$red1);
imageline($im,0,$px+200,400,$px+200,$red1);

}
imageline($im,0,200,400,200,$white);
imageline($im,200,0,200,400,$white);
imageline($im,195,5,200,0,$white);
imageline($im,205,5,200,0,$white);
imageline($im,395,195,400,200,$white);
imageline($im,395,205,400,200,$white);
imagestring($im,10,385,200,"X",$white);
imagestring($im,10,185,0,"y",$white);
for(
$px=-400;$px<400;$px=$px+0.1)
{
$x=$px/20;
if(
$x!=0)
{
$y=sin($x);
}
$py=-$y*20;
imagesetpixel($im,$px+200,$px+200,$white);
}
imagepng($im);
imagedestroy($im);

?> ;


LZ的程序有处错误,

[复制到剪切板]
CODE:
imageline($im,195,5.200,0,$white);//imageline($im,195,5,200,0,$white);符号错了 ;

生成的图像是一个二维的坐标系,y=-x