Question of Pointer

Why output of this 2 program is different?

P1:
float a=2,*f1,*f2;
f1=f2=&a;
*f1+=(a+=2.5);
printf(“\n%f %f %f”,a,*f1,*f2);

P2:
float a=2,*f1,*f2;
f1=f2=&a;
a+=(a+=2.5);
printf(“\n%f %f %f”,a,*f1,*f2);

Output: (In GCC and Turbo C both)

6.500000 6.500000 6.500000
9.000000 9.000000 9.000000