用PHP实现九九乘法表

九九乘法表可以用循环语句来实现。下面是一个简单的例子：

for ($i = 1; $i <= 9; $i++) {
    for ($j = 1; $j <= $i; $j++) {
        echo "$i x $j = " . $i * $j . " ";
    }
    echo "<br>";
}

上面的代码使用两个嵌套的循环，第一个循环用来控制行数，第二个循环用来控制列数。在每一行的循环中，我们输出每一列的乘法结果，然后在每一行之后换行。

输出结果如下：

1 x 1 = 1
2 x 1 = 2 2 x 2 = 4
3 x 1 = 3 3 x 2 = 6 3 x 3 = 9
4 x 1 = 4 4 x 2 = 8 4 x 3 = 12 4 x 4 = 16
5 x 1 = 5 5 x 2 = 10 5 x 3 = 15 5 x 4 = 20 5 x 5 = 25
6 x 1 = 6 6 x 2 = 12 6 x 3 = 18 6 x 4 = 24 6 x 5 = 30 6 x 6 = 36
7 x 1 = 7 7 x 2 = 14 7 x 3 = 21 7 x 4 = 28 7 x 5 = 35 7 x 6 = 42 7 x 7 = 49
8 x 1 = 8 8 x 2 = 16 8 x 3 = 24 8 x 4 = 32 8 x 5 = 40 8 x 6 = 48 8 x 7 = 56 8 x 8 = 64
9 x 1 = 9 9 x 2 = 18 9 x 3 = 27 9 x 4 = 36 9 x 5 = 45 9 x 6 = 54 9 x 7 = 63 9 x 8 = 72 9 x 9 = 81