C语言运算符

Question

#include <stdio.h>  

int main() 
{

    int a=-1?2:5 + 8?4:5;
    printf("%d\n",a);
    return 0;
}

上面程序的输出是2。但是为什么呢？请解释一下

Answer 1

编写人类可读且可理解的代码。 (至少，尝试...)

 int a=-1?2:5 + 8?4:5;

与

相同

int a = (-1) ? 2 : ( 5 + ( 8 ? 4 : 5) );

^{引用:Operator Precedence}

现在，让我们将其与三元运算符条件进行比较，如 C11 第 §6.5.15 章中所述，

The first operand is evaluated; there is a sequence point between its evaluation and the evaluation of the second or third operand (whichever is evaluated). The second operand is evaluated only if the first compares unequal to 0; the third operand is evaluated only if the first compares equal to 0; the result is the value of the second or third operand (whichever is evaluated),

所以，就你而言，

• 第一个操作数不等于零
• 因此，它计算第二个操作数，并将结果(操作数的值)返回并存储到赋值运算符的 LHS 变量中。