How to Extract float from string

Hi ,I need some help .
I use the arduino to receive the data from usb ,the data like this :X100.2 Y600.3 U8.3 I70.6
Now ,I want to extract the float to the another variable.like theis :
a,100.2
b,600.3
c,8.3
d.70.6
How I can do it ?
I am a newbie ,
please write the full code ,thanks for your help .
Thanks very much .