Is there a more elegant way to do the following in C++11?

I want to avoid warnings about a comparison between unsigned int and signed int.

I use loops such as:

for (int i =0 ; i < vec.size(); i++) {
 // do something
}

which gives these warnings (which by itself is fine, I want high-level of warnings).

I thought of changing it to the following:

for (auto i = vec.size()*0; i < vec.size(); i++) {
 // do something
}

in which case I don't get the warnings. But I am wondering if there is something more elegant than that, that would automatically deduce the type required for the iterator.