注意，这里使用了 (i+1)，因为数组中第一个元素的索引号是 0，要从第一个元素开始，必须加上 1。
Note that you use (i+1) because in the array, the counter value of the first element is zero; as you want to start with the first element, the 1 is added.
比如，你有没有发现在数组索引里没有用引号将字符串括起来？
For instance, did you notice that there were no single quotes around the array indexes ($x[sales] and $x[profit])?
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