Operations with same meaning

[filippo . ferrara]

unsigned short pippo;

1) pippo = pippo & 0x00FF;
2) pippo &= 0x00FF;

In line 2, no warning is pointed out, while in line 1 is pointed out a warning of 
assignment of int
to unsinged int
Why? Haven't them the same  meaning?

Best regards
Ferrara Filippo