Is It Ever Good Practice To Modify The Index Variable Inside a FOR Loop?

Question

Given the code:

for (int i = 1; i <= 5; i++)
        {
            // Do work
        }

Is is ever acceptable to change the value of i from within the loop? For example:

for (int i = 1; i <= 5; i++)
        {
            if( i == 2)
            {
               i = 4;
            }
            // Do work
        }

Answer 1

In my opinion, it is too confusing. Better use a while loop in such case.

Answer 2

It is acceptable, however, I personally think this should be avoided. Since it's creating code that will be unexpected by most developers, I find that it's causing something much less maintainable.

Personally, if you need to do this, I would recommend switching to a while loop:

int i=1;
while (i <= 5)
{
    if (i == 2)
        i = 4;

    ++i;
}

This, at least, warns people that you're using non-standard logic.

Alternatively, if you're just trying to skip elements, use continue:

for (int i = 1; i <= 5; i++)
{
    if (i == 2 || i == 3)
       continue;
}

While this is, technically, a few more operations than just setting i directly, it will make more sense to other developers...