To answer your question, the ++i will increment the value of i, and then return the incremented value.
i = 1; j = ++i; (i is 2, j is 2) whereas, the i++ will increment the value of i, but return the original value that i held before being incremented.
i = 1; j = i++; (i is 2, j is 1)
For a for loop, either works. ++i seems more common. However, in any case, follow the guideline "prefer ++i over i++" and you won't go wrong.
You can verify this by looking at the generated code, which will be identical.