了解逗号运算符

Question

int main()
{
    int a = (1,2,3);
    int b = (++a, ++a, ++a);
    int c= (b++, b++, b++);
    printf("%d %d %d", a,b,c);
}

我是编程初学者。我不明白这个程序如何显示 6 9 8 的输出。

Answer 1

三个声明中都使用了,

int a = (1,2,3);
int b = (++a, ++a, ++a);
int c = (b++, b++, b++);

是comma operator。它计算第一个操作数 ¹ 并丢弃它，然后计算第二个操作数和 return 它的值。因此，

int a = ((1,2), 3);          // a is initialized with 3.
int b = ((++a, ++a), ++a);   // b is initialized with 4+1+1 = 6. 
                             // a is 6 by the end of the statement
int c = ((b++, b++), b++);   // c is initialized with 6+1+1 = 8
                             // b is 9 by the end of the statement.

_{1 对于逗号运算符，计算顺序保证从左到右。}

Answer 2

代码一点也不好，任何头脑正常的人都不会写它。那种代码大家不要花时间看，不过我还是会给出解释的。

逗号运算符,表示“做左边的，丢弃任何结果，做右边的，然后return结果。将部分放在括号中对结果没有任何影响功能。

写得更清楚的代码是：

int a, b, c;

a = 3; // 1 and 2 have no meaning whatsoever

a++;
a++;
a++;
b = a;

b++;
b++;
c = b;
b++;

前增量运算符和 post 增量运算符在它们的行为方式上有所不同，这会导致 b 和 c 的值不同。

Answer 3

I am beginner in programming. I am not getting how does this program shows me output of

明白就好comma operators and prefix ,postfix.

根据提供给您的链接中提到的规则

int a = (1,2,3);          // a is initialized with 3 last argument .
int b = (++a, ++a, ++a);  // a is incremented three time so becomes 6 and b initilized with 6 . 
int c = (b++, b++, b++);  // b incremented two times becomes 8  and c initialized with  8.
                          // b incremented once more time becomes 9

了解逗号运算符

Understand comma operator

c

comma-operator