Anyone can help?

[Tinker]

If we used an array of many structures such as:

struct instruction array[1000];

and this array holds 500 instructions from array[0] to array[499], how
can a new instruction be inserted between the 2nd and 3rd
instructions? Why is a linked list preferable in this situation?

please help
thanks

 

[Joona I Palaste]

If we used an array of many structures such as:

struct instruction array[1000];

and this array holds 500 instructions from array[0] to array[499], how
can a new instruction be inserted between the 2nd and 3rd
instructions? Why is a linked list preferable in this situation?

You'll have to move the other instructions by hand to make room for the
new instruction. This would involve 498 assignment operations.
A linked list is preferable because in a linked list, insertion (once
you know where to insert) takes O(1) time instead of O(n). You simply
assign one pointer to point somewhere else. For details, ask your
teacher.

 

[David Resnick]

If we used an array of many structures such as:

struct instruction array[1000];

and this array holds 500 instructions from array[0] to array[499], how
can a new instruction be inserted between the 2nd and 3rd
instructions? Why is a linked list preferable in this situation?

please help
thanks

Inserting into arrays requires copying the array elements
at and beyond the insertion point. This can be expensive.
For example, in your case, you'd have to do something like:
/* copy elements upwards */
memmove(&array[3], &array[2], sizeof(struct instruction) * 498);
/* fill in new instruction */
array[2].field1 = 1;
array[2].field2 = 2; /* ... */

Whether this is a good idea depends on your application. If you
are inserting relatively rarely, want random access, and don't
care about pointers to individual instructions getting invalidated
by the copying, well, the array may be what you want.

If you are inserting often, don't care about random access, and want
insertion not to invalidate pointers to individual members, a linked
list is a fine choice. Insertion just involves fiddling with a few
pointers.

-David