布尔/用C逻辑运算都需要产生0或1。

从ISO C99标准的部分6.5.3.3/5：

  

逻辑否定运算符的结果！ 0如果操作数的值进行比较，不等于0，1，如果它的操作数的值进行比较，等于0

块引用>

其实，！X 是强制的值是一个常见的​​成语是0或1（我个人preFER X ！= 0 ，虽然）。

也看到从comp.lang.c常见问题解答 Q9.2。

I know that in C, for if statements and comparisons FALSE = 0 and anything else equals true.

Hence,

int j = 40
int k = !j

k == 0 // this is true

My question handles the opposite. What does !0 become? 1?

int l = 0
int m = !l

m == ? // what is m?

Boolean/logical operators in C are required to yield either 0 or 1.

From section 6.5.3.3/5 of the ISO C99 standard:

The result of the logical negation operator ! is 0 if the value of its operand compares unequal to 0, 1 if the value of its operand compares equal to 0.

In fact, !!x is a common idiom for forcing a value to be either 0 or 1 (I personally prefer x != 0, though).

Also see Q9.2 from the comp.lang.c FAQ.