NOT(〜)vs否定(！) [英] NOT(~) vs NEGATION(!)

问题描述

#include <iostream>

using namespace std;
int main(int argc, char *argv[]) 
{
   int i=-5;
   while(~(i))
   {
      cout<<i;
      ++i;
   }

 }

输出为-5，-4，-3，-2. 它不应该打印直到-1的值吗?为什么只显示-2? 并且请向我解释非"运算符和否定"运算符之间的区别.每当我编写程序时，它们都是错误的来源.

The output is -5,-4,-3,-2. Shouldn't it print values till -1?Why is it only till -2. And please explain me the difference between 'not' and 'negation' operators.When ever I write a program they were the source for bugs.

while(i)

我知道循环条件对于正数和负数(除0外)都是正确的.

I know that the loop condition will be true for positive and negative i's except 0.

while(!i) vs while(~i)

对于上面两个循环执行的'i'值是什么?

For what values of 'i' the above two loops get executed?

推荐答案

当i到达-1时，~i的值是~-1或0，因此while循环停止执行. !运算符之所以起作用，是因为它做了完全不同的事情.对于0值，其结果为1，对于所有其他值，其结果为0. ~是按位取反.

When i gets to -1, the value of ~i is ~-1, or 0, so the while loop stops executing. The ! operator works because it does something completely different; it results in 1 for 0 values and 0 for all other values. ~ is a bitwise negation.

更多细节:

• ~接受数字中的每个位并进行切换.因此，例如10010 ₂ 将变为01101 ₂
• -1当二进制补码有符号整数时都是二进制的.
• ~0b…11111111是0.

• ~ takes each bit in a number and toggles it. So, for example, 10010₂ would become 01101₂
• -1 is all ones in binary when a two's complement signed integer.
• ~0b…11111111 is 0.

但是:

• !0是1，!anythingElse是0
• -1不是0
• !-1仍然是0

• !0 is 1, !anythingElse is 0
• -1 is not 0
• !-1 is still 0

如果您实际上想循环包含i == -1，只需使用while (i)而不是while (~i).

And if you actually want to loop including i == -1, just use while (i) instead of while (~i).

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