Constant array is given in the first case. sizeof(a) will provide us with the value of 12, and sizeof(a) - with that of 4. 12/4 = 3
In the second case, sizeof(b) will provide us with the value of 4, since a is a pointer and it takes 4 bytes, sizeof(a) is also equal to 4. 4/4=1
The third case is similar to the second one.