Question

I think I will get 12, not 7.
w++, then w will be 4, which is 100, and w++, w will be 8, 1000;
so w++|z++ will be 100|1000 = 1100 will be 12.

what’s wrong with me?

int main()
{
    int  w=3, z=7; 
    printf("%d\n", w++|z++);
}

Answer 1

The problem is that by using w++|z++, you’re first using the value of w and ORing that by the current value of z, then incrementing each. Use ++w|++z instead, and the numbers will first be incremented, then used.

int main()
{
    int x = 10;

    // prints 10
    printf("%d\n", x++);
    // prints 11
    printf("%d\n", x);

    x = 10;
    // prints 11
    printf("%d\n" ++x);
    // prints 11
    printf("%d\n" x);
}

The same can be done with --x and x--. For more information, see this relevant question.