1) code segement 2: Should be:
struct object_struct objects[10];

2) code segement 3:
You should declare i at the top instead of x
The 1st for loop should use “i” as the counter as you use it later and haven’t declared it.

3) code segement 3: Inside 1st for loop should be
object[i].x = rand() % 640 + 1;
object[i].y = rand() % 480 + 1;
object[i].on_screen = true;

4) code segment 3: Your outside screen logic is wrong, it should be:
object[i].y > 480 || object[i].y < 0 || object[i].x > 640 || object[i].x < 0

I have made the corrections to the PDF versions and will email them to you now.