I think the best option is to use getline() and then iterate over the string and enter into the array from the string.
If the OP's sure that's how the input will come in all the time, the OP can use cin. That just won't make it very robust/flexible...
It just depends on who is going to be using it and for how long. If it's just to run this single simulation and you're sure all the data is only separated by spaces, then I'd recommend cin - it's easy, you don't have to worry about too much. But if multiple simulations are going to be run (like if you do other experiments later and want to use this sort of input method to run some other calculation), I'd agree with ilikepython and say use getline().