Double precision?

[TheDGuy via Digitalmars-d-learn]

I don't know what my computer is doing today:

code:
                double normalized_i = (x / width) - 0.5;
                double normalized_j = (y / height) - 0.5;
                writeln(x);
                writeln(normalized_i);
                writeln(y);
                writeln(normalized_j);
x and y are coordinates and if x is any number from 0 to 150 the 
result of x/width is always zero, how can that be (width is never 
0)? Another video: https://youtu.be/Fysv2fOwtk4