Programming PHP

Number of Operands
Most operators in PHP are binary operators; they combine two operands (or expressions)
into a single, more complex expression. PHP also supports a number of unary
operators, which convert a single expression into a more complex expression.
Finally, PHP supports a single ternary operator that combines three expressions into
a single expression.
Operator Precedence
The order in which operators in an expression are evaluated depends on their relative
precedence. For example, you might write:
2 + 4 * 3
As you can see in Table 2-3, the addition and multiplication operators have different
precedence, with multiplication higher than addition. So the multiplication happens
before the addition, giving 2+12,or14, as the answer. If the precedence of addition
and multiplication were reversed, 6*3, or 18, would be the answer.
To force a particular order, you can group operands with the appropriate operator in
parentheses. In our previous example, to get the value 18, you can use this expression:
(2 + 4) * 3
It is possible to write all complex expressions (expressions containing more than a
single operator) simply by putting the operands and operators in the appropriate
order so that their relative precedence yields the answer you want. Most programmers,
however, write the operators in the order that they feel makes the most sense
to programmers, and add parentheses to ensure it makes sense to PHP as well. Getting
precedence wrong leads to code like:
$x + 2 / $y >= 4 ? $z : $x