PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

42 Chapter 1 PHP Crash Course
Figure 1.5
The totals of the customer’s order have been calculated,
formatted, and displayed.
It also uses the number_format() function to format the totals as strings with two
decimal places.This is a function from PHP’s Math library.
If you look closely at the calculations, you might ask why the calculations were performed
in the order they were. For example, consider this statement:
$totalamount = $tireqty * TIREPRICE
+ $oilqty * OILPRICE
+ $sparkqty * SPARKPRICE;
The total amount seems to be correct, but why were the multiplications performed
before the additions? The answer lies in the precedence of the operators—that is, the
order in which they are evaluated.
Understanding Precedence and Associativity
In general, operators have a set precedence, or order, in which they are evaluated.
Operators also have an associativity, which is the order in which operators of the same
precedence are evaluated.This order is generally left to right (called left for short), right
to left (called right for short), or not relevant.
Table 1.7 shows operator precedence and associativity in PHP. In this table, operators
with the lowest precedence are at the top, and precedence increases as you go down the
table.