Question 1

I have a struct like,

struct foo
{
    int a;
    char c;
};

When I say sizeof(foo), i am getting 8 on my machine. As per my understanding, 4 bytes for int, 1 byte for char and 3 bytes for padding. Is that correct? Given a struct like the above, how will I find out how many bytes will be added as padding?

Question 2

I am aware that sizeof can be used to calculate the size of an array. Mostly I have seen the usage like (foos is an array of foo)

sizeof(foos)/sizeof(*foos)

But I found that the following will also give same result.

sizeof(foos) / sizeof(foo)

Is there any difference in these two? Which one is preffered?

Question 3

Consider the following statement.

foo foos[] = {10,20,30};

When I do sizeof(foos) / sizeof(*foos), it gives 2. But the array has 3 elements. If I change the statement to

foo foos[] = {{10},{20},{30}};

it gives correct result 3. Why is this happening?

Any thoughts..