Search:

Look at this
ships[i].x_coord = ships[i].x_coord + rand() % 100;

Now look at this
if (spaceShip ships[i] > highestValue)

It seems you copied the whole type and variable name from the...

spaceShip createShips (spaceShip ships[], int size)
{
for (int i = 0; i < size; i++)
{
ships[i].x_coord = rand() % 1024;
ships[i].y_coord = rand() % 768;
}
//...