Why padding are added, if char comes after int?

Question

For example, there is a structure

struct A
{
char a;
int i;
};

In this case, we have a[1 byte] + padding[3 byte] + int[4 byte] = 8.

Answer 1

Not only each member of the struct has to be data aligned, but the struct itself has to aligned to the size of the largest member in the struct. So, padding is added to struct A such that its size should be a multiple of the larger of sizeof i and sizeof a.

Have a look at C FAQ here