将NSString转换为Int，然后使用该值确定要在UILabel中显示的文本

I have my weather station app I am working on, it all works but the one thing I want to do is with the UV rating there is usually and word rating associated with the number. (Ex - UV rating is less then 3, word accompniing it "Low", between 3-6, "Medium" and etc...) How do I convert my NSString, which displays the value into and int and then assign a word based on the range in which that value falls in.I have my weather station app I am working on,