How can I add a bullet every time the player clicks?

Question

I'm not understanding how to dynamically add object instances in my games.

I'm really having trouble understanding the general concept. If I want to quickly generate unknown numbers of objects, going through and declaring them one by one does not seem to be plausible. This problem is exemplified by bullets. If the player can fire 100 bullets, how do I declare and define these objects in a simple manner. Obviously I need formulas to tell the bullets where to appear and where to go, but I can do that. How do I get to the point where I can begin to define those formulas?

Here is the code up to the point I have tried, the current problem being that B cannot be assigned because it is the essence of the foreach loop:

if (ms.LeftButton == ButtonState.Pressed)
{
    shotFired = 0;
    foreach (Bullet B in bulList)
    {
        if(B != null)
        {
            B = new Bullet(main.Location, enball, spriteBatch);
            shotFired = 1;
        }
     }
    //if all bullets are not "null," essentially delete one and replace it.
}

Answer 1

To fire a bullet every time the mouse is clicked, with no limit to the number of bullets that can exist, simply do:

if (ms.LeftButton == ButtonState.Pressed) {
  var bullet = new Bullet(main.Location, enball, spriteBatch);
  bulList.Add(bullet);
}

If you want to have a fixed number of bullets (represented by bulList) and use the first null entry in the list you find to hold the newly-fired bullet, use a for loop instead (because as you noted, you cannot modify the foreach enumeration variable in that fashion):

if (ms.LeftButton == ButtonState.Pressed) {
  for (var index = 0; index < bulList.Count; ++index) {
    if (bulList[index] == null) {
      bulList[index] = new Bullet(main.Location, enball, spriteBatch);
      break;
    }
  }
}

You can also implement that "if no bullets were null, re-use an existing one" logic in the latter example if you like.

Note that a better way to handle the above is to instead partition your list and keep a "dead index" such that every live bullet is below the dead index and every dead (null) bullet is above it. This can help you avoid the costly linear search through the bullet array every time you fire.

Answer 2

This is a very simple question.
When you get the click event, add a new bullet into your bullet array. Then, you can update and draw the bullets at their positions every frame. When you update bullets, you can make them go forward, and check their collisions with objects. Then just draw them.
It is not as hard as you think.
Here are some links:
http://en.wikibooks.org/wiki/Creating_a_Simple_3D_Game_with_XNA
http://www.riemers.net/