C/CPP运算优先级的坑及解决_开发_开发者

开发者 https://www.devze.com 2023-11-20 13:34 出处：网络作者： _不会dp不改名_

目录C/CPP运算优先级坑1. 位运算优先级低于比较运算符2. 移位运算符优先级低于算术运算符C语言运算优先级口诀总结C/CPP运算优先级坑

C/CPP运算优先级坑

1. 位运算优先级低于比较运算符

做leetcode时遇到的，判断一个数某一比特位是否为0。

if ( val & 2 == 0) {
	// do someting...
}

万万没想到&运算符的优先级是低于==的，debug了好久，得加上括号。

1.1 验证

#include <IOStream>
int main( int argc, char *argv[]){
    int val = 2;
    if ( val & 1 == 0) {
        std::cout << "without (): bit 1 is 0" << std::endl;
    }
    else {
        std::cout << "without (): bit 1 is 1"php << std::endl;
    }
    if ( (val & 1) == 0) {
        std::cout << "with (): bit 1 is 0" << std::endl;
    }
js    else {
        std::cout << "with (): bit 1 is 0" << std::endl;
    }
    return 0;
}

输出结果为

without (): bit 1 is 1
with (): bit 1 is 0

2. 移位运算符优先级低于算术运算符

这是在写二分的时候遇到的, l +　(r-l) >> 1 的值永远为r >> 1

应该写作l + (r - l >> 2)。

2.1 验证

#include <iostream>
int main( int argc, char *argv[]){
    int l = 2, r = 8python;
    int mid = l + (r - l) >> 1;
    int mid2 = l + ( r - l >> 1);
    std::cout << "mid: " << mid << std::endl;
    std::cout javascript<< "mid2: " << mid2 << std::endl;
    return 0;
}

输出结果为