Question

I am confused about this code: (http://www.joelonsoftware.com/articles/CollegeAdvice.html)

while (*s++ = *t++);

What is the order of execution? Is *s = *t first done, and then are they each incremented? Or other way around?

Thanks.

EDIT: And what if it was:

while(*(s++) = *(t++));

and

while(++*s = ++*t);

Answer 1

while (*s++ = *t++);

From the precedence table you can clearly see ++ is having higher precedence than *. But ++ is used here as post increment operator, so the incrementation happens after the assignment expression. So *s = *t happens first, then s and t are incremented.

EDIT:

while(*(s++) = *(t++));

Is same as above. You are making it more explicit with the use of parenthesis. But remember ++ is still a post increment.

while(++*s = ++*t);

There is just one operator next to s. So * is applied first and on that result ++ is applied which results in the lvalue required error.

while(*++s = *++t);

Again just operator next to s,t. So the incrementation happens first followed by copy. So we are effectively skipping the copy of the first char from t to s.