The priority of && and || in C++ programming

Reprint https://zhidao.baidu.com/question/426219427238900292.html

Question:

In this program, why not execute (++y)&&(++x) first? The program first judges x>y, and then the latter part of the expression is short-circuited. && is not higher priority than ||? How to explain.

Reply:

C/C++ has a short-circuit effect A || B in the logical judgment expression.
When A is logically true, the value of the entire expression can be determined to be true, and B does not execute
A && B. When A is logically false When the value of the entire expression can be determined to be false, B will not be executed.
Here x>y is true, so the following (++y)&&(++x) will not be executed.

Ask

当&&和||同时存在的时候，即 A || B && C 的时候，为什么不是先计算B&&C？

Follow up

如果A已经是逻辑真，就没必要再计算B&&C了。虽然&&的优先级比||高，用括号括起来看是这样：(A) || (B && C)，
A和B&&C是同等优先运行的表达式，按照从左至右的运行规则，先计算A，发现A为逻辑真后，B&&C就不执行了。

 

优先级高只是结合（律）的问题（即括号怎么放的问题），但不是计算的先后顺序。