Your VFR array should have values 0, 250, 500 ... 4000. Your density array will have to be the same length. Your for loop will iterate the (lesser) number of times defined by your arrays. So, since your density array has 0 elements, it runs 0 times.
I don't understand what you mean. On the front panel I have the density having 17 slots for data to be placed in. Also The VFR does not execute the 0 to 4000.
I am referring to this picture of the front panel you uploaded. VFR and density are inputs in your code. Your For Loop will run a certain number of times, defined by the SMALLEST of: the count terminal (N), the size of array "density", the size of array "VFR".
When elements are grayed out on your front panel, that means they are not part of your array, it doesn't matter how many you are showing. So VFR has 1 element, and density has 0 elements, and your For Loop will run 0 times. For VFR, it sounds like you already know what you want, so you can type those values in or create them with a ramp function. For density, you can also type the values in, but if it is a constant (0.072?) then change it to a single element instead of an array.