资 源 简 介
Each operator has a precedence number assigned to it that determines the order in which
the operator and its operands are evaluated. The precedence numbers range from 1 （the
highest precedence， that is， first evaluated） to 7 （the lowest precedence， that is， last
evaluated）。
The following rules determine how expressions are evaluated：
● The highest precedence operators are evaluated first， then the second highest
precedence operators， and so on unTIl the lowest precedence operators are evaluated.
● Operators of equal precedence are evaluated from left to right in the expression.
● Parentheses （ and ） can be used for grouping operators and operands and for
controlling the order in which the expressions are evaluated. For example， the
folloin exression ealuates to
