I've lived in various neighborhoods in the city for about 8 years, have friends who've been here for 10+ years, and none of them has ever been the victim of a violent crime. The worst that's happened to me is having a bike stolen (Chicago is one of the worst cities for bike theft for some reason). I host many foreign visitors for work, usually every month or so, and just about every one has remarked at what a tourist-friendly city it is.

For some perspective, there are just under 2.7 million year-round residents within the city limits, and another 7 million or so in the greater metropolitan area. In 2010* there were more than 39 million visitors to the city, including over 1 million foreign visitors. From a purely statistical perspective, your odds of having trouble during a four day trip are quite small. Enjoy!


*
http://www.explorechicago.org/etc/me...stics_2010.pdf