了解"for"循环的退出条件 [英] Understanding the exit condition of a 'for' loop

问题描述

阅读了堆栈溢出问题后，我有这个问题 使用C 以二进制表示形式打印int.

I had this question after reading the Stack Overflow quesion Print an int in binary representation using C.

在用户评论中，他们发布了此for循环，该循环将1或0分配给位位置，以便从int十进制转换为char *二进制.

In a user's comment, they posted this for loop, which assigns either a 1 or a 0 to the bit position in order to convert from an int decimal to char * binary.

for(; bits--; u >>= 1)
    str[bits] = u & 1 ? '1' : '0';

我了解为什么不需要初始化值.这是我一直都知道的for循环的语法:

I understand why there doesn't need to be an initialized value. This is the syntax for a for loop that I've always known:

for ( variable initialization; condition; variable update )

我不明白"bit--"如何成为退出条件.请帮助我理解此代码的工作方式(我已经对其进行了测试，并且它是有效的).

I don't understand how 'bit--' can be an exit condition. Please help me understand how this code works (I tested it, and it is valid).

推荐答案

在C中，布尔值上下文中的零值计算为假".因此，当bits--评估为0时，在循环上下文中，其评估为"false"并终止循环.

In C, a value of zero evaluates to "false" in a boolean context. So when bits-- evaluates to 0, in the context of the loop it evaluates to "false" and terminates the loop.

例如，如果您说:

int x = 1;
if (--x)
{
  printf("True!\n");
}
else
{
  printf("False!\n");
}

它将输出"False"，因为--x的计算结果为0，在布尔上下文中为"false".

It will output "False", because --x evaluates to 0, which is "false" in a boolean context.

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