Using structures in C

Question

I have two structures-

typedef struct Element
 {
  int a;
 }Element;

typedef struct List
 {
  Element * E;
 }List;

How can I add elements in the array E?I am trying to do this but this is not working-

List list;
list.E=calloc(5,sizeof(int));
for(i=0;i<5;i++) 
  (list.E+i)->a=2;

What is wrong in this??

Answer 1

Try this

List list;
/* you dont need calloc at all here */
list.E = malloc(5 * sizeof(Element));
if (list.E != NULL) /* check that malloc succeeded before dereferencing the pointer */
{
    for (i = 0 ; i < 5 ; i++) 
        list.E[i].a = 2;
}

you need to allocate 5 * sizeof(Element) bytes in order to store 5 instances of the struct Element, and then to access the element you just need the array subscript operator [].

Note that, sizeof(Eelement) != sizeof(int), and that's why your program was not working.

Also, the way your are indexing your array is confusing, the way I show in this answer I think is very easy to follow.