php判断&选择&循环应用

<?php
$num=rand(1, 100);
if ($num%2==0) {
echo '$num='.$num;
echo '<br>$num是偶数';
}
echo "</br>"; //rand()函数和if判断语句的应用

$month=date("n");
$today=date("j");
if ($today>=1 and $today<=10) {
echo "今天是".$month."月上旬".$today."日";
}
elseif ($today>10 and $today<=20){
echo "今天是".$month."月中旬".$today."日";
}
else {
echo "今天是".$month."月下旬".$today."日";
} //if...else语句的应用

$sum=1;
for ($i=1;$i<=100;$i++) {
$sum*=$i;
}
echo "\$sum=".$sum; //for循环语句的应用