postfix and prefix increment operator in a for loop

Possible Duplicate:
Difference between i++ and ++i in a loop?

Can anyone explain what's the difference between those:

for(unsigned col = 0; col < n; ++col, num_to_fill >>= 1U)
{

    for(unsigned row = num_to_fill; row < (1U << n); row += (num_to_fill * 2))
    {
        std::fill_n(&output[col][row], num_to_fill, 1);
    }
}

and

for(unsigned col = 0; col < n; col++, num_to_fill >>= 1U)
{

    for(unsigned row = num_to_fill; row < (1U << n); row += (num_to_fill * 2))
    {
        std::fill_n(&output[col][row], num_to_fill, 1);
    }
}

When col=0 , In ex.1 Output[col][row] will be output[1][row] and In ex.2 Output[col][row] will be output[0][row] . Am I right ?

Question 2 : Would using >>= 1U instead of /= 2 make any difference ?