c中运算符的分配和优先级

Question

In the following code :

int main()
{
    int x = 2, y = 1;
    x *= x + y;
    printf("%d\n", x);
    return 0;
}

How is the operators precedence work ? , as * has a higher precedence than + so I expect that multiplication operation should be done first however the result shows that it is calculated as x * = (x+y) so the addition is done first !

The same confusion here in the following code :

  int main()
    {
        int x = 2, y = 2;
        x /= x / y;
        printf("%d\n", x);
        return 0;
    }

dont know how the operators precedence will work ... Thanks for anyone has an explanation.

Answer 1

The shorthand operators (*=, /= etc.) have lower precedence than single (+, / etc.) operators.

See: http://en.wikipedia.org/wiki/Operators_in_C_and_C%2B%2B#Operator_precedence

Answer 2

The Precedence of operators is still the same. * has a higher precedence than +. However, since you're using *= you are waiting for the operation to be completed first before multiplying.

It's basically the same thing is (x + y) * x

Answer 3

Given identifiers a and b , an operator of the form a op= b (where op can be + , * , etc.), is entirely equivalent to (a) = (a) op (b) , with the only difference being that (a) is only evaluated once.

The comma operator has the lowest precedence.