For one, there's a lot wrong with this line. First, your closing } should be a ), and you shouldn't have a semi-colon there. You also never increment i, so if the loop starts, it will never stop.
I have no idea what the "correct" thing here is, but maybe you wanted something like
1 2 3 4
for (int i = 1; i < N && i > a[i].v; i++)
{
a[i].p = i; // no idea if this is what you want
}
Compiler errors have lines associated with them. If you get an error, look for errors in the surrounding lines that the error message gives you.