More efficient way to do this?

1

Hello everyone, it seems like there’s probably a equation to make this more efficient, but I’m not the math whiz that many others may be.

Is there a simpler way to do this?:


switch (num) {
	case 1:  pn = 0;  break;
	case 2:  pn = 2;  break;
	case 3:  pn = 4;  break;
	case 4:  pn = 6;  break;
	case 5:  pn = 8;  break;
	case 6:  pn = 10; break;
	case 7:  pn = 12; break;
	case 8:  pn = 14; break;
	case 9:  pn = 16; break;
	case 10: pn = 18; break;
	case 11: pn = 20; break;
        //and it keeps going.....
}

In words what’s happening is that for every incremental number it goes to the next even number to process.

Any help would be greatly appreciated.