else if 相匹配規則
The rule is that an else goes with the most recent if unless braces indicate otherwise
&& || ！Precedence
The ! operator has a very high precedence—higher than multiplication, the same as the
increment operators, and just below that of parentheses. The && operator has higher
precedence than ||, and both rank below the relational operators and above assignment in
precedence. Therefore, the expression
a > b && b > c || b > d
would be interpreted as
((a > b) && (b > c)) || (b > d)