expression window float support

Hi

This can sound a weird problem,I have some float variables added in expression window,which doesnot show up its value and neither printf support float variable.

I changed properties as

by going to Project -> Properties -> C/C++ Build -> Settings -> Cross ARM C Linker -> Miscellaneous -> User float with nano printf

I don't understand reason for it.

watch window also doesnot show float variable ,just shows nan as above