do{ 语句块;
}while(表达式);//表达式为循环条件

<?php
header("Content-type:text/html;charset=utf-8");
$i = 1;
$sum=0;
do {
        $sum += $i;
        $i++;
    } while ($i <= 100);
echo '1 + 2 + 3 +...+ 99 + 100 = '. $sum;
?>