You are doing integer division.
Try the following and it will work as expected:
int x = 17;
double result = 1.0 / x;
The type of the 1 in the expression you have above is int, and the type of x is int. When you do int / int, you get an int back. You need at least one of the types involved to be floating point (float or double) in order for floating point division to occur.
Unlike in Mathematics, division in C++ can either refer to truncated integer division (what you did) or floating point division (what I did in my example). Be careful of this!
In my example, explicitly what we have is double / int -> double.
