Field Not Support 0.XXX

Dear Sir,

I need your help to take a look on my below script.When I press 2 at the PART_COST field it auto came out A-ITEM, but when I press 0.23 nothing coming out at both PART_COST and COST_GROUP. I was using INT and it support negative, do INT support 0.XXX is it cause by this. after I add value nothing coming out
Second I meed to put a range like below, I want 0.199 below is ITEM-C and 0.2 - 0.99 is ITEM-B may you help me please
if ($values["PART_COST"]>1)

$values["COST_GROUP"] = "A-ITEM";

if ($values["PART_COST"]==0.2<1)

$values["COST_GROUP"] = "B-ITEM";

if ($values["PART_COST"]<0.199)

$values["COST_GROUP"] = "C-ITEM";