2D Game Engine (Help)

An easy way to do it is to have a Game_Mode int, and every frame perform a switch statement on that int. The following example assumes everything is hard coded.

So, initialise the int to 0 = main menu mode.
In main menu mode, render a background and the various choices that can be made (at it's most simple, present the player with one option "press enter to start game").
The player presses enter, and Game_Mode is changed to 1 = character select mode.
Character select mode renders the character choices and allows the player to highlight the various characters. When enter is pressed, the highlighted character is noted (eg, player_character = 3) and the game enters mode 2 = load level.

Perform a switch statement on Level_Number. Let's say this defaults to level 1. The game will see that Level_Number == 1, and you will have supplied it data which says what level one entails (eg, enemy placement, item placement, terrain, etc). Once the level data is converted into some kind of functional form (eg, enemy and item classes are added to a linked list, the level terrain is loaded into an array), set the Game_Mode to 3 = run level.

Here, the level is rendered, enemies move around, the player's input controls the character, physics and collision detection are carried out, etc.
Once the player position is at the end of the level (eg, x > 10000), Game_Mode becomes 4 = Level Wrap up. The players stats are displayed.
The player presses fire or some such, the Level_Number is incrimented to 2, Game_Mode changes to 2 to load the level, the level is loaded, game mode changes to 3, the next level is played, etc. etc.

Once Level_Number = 10 (or whatever) Game_Mode is set to 5 = spectacular ending sequence, and you're done.

I would prefer a stack based task system (although your kernel has all the standard tasks all the time, but your current game task is determined by the stack), if you don't know what a stack is; its basically a stack of pancakes, first in -> last out, so your main menu goes on first and then it decides what task goes on after it eg skirmish or campaign and when your current game task finishes, it automatically goes back to the previous one. Nifty eh?

Great, thanks.

Now, I know the game needs an image class, an animation cls, level, sound, character, enemy, maybe bullet.cs, etc.
How should these be implemented, what methods MUST they contain, etc.

Maybe giving me a list of all the classes needed to make a game like the one I said above might give me an idea of how everything works.

Thanks,

you may be getting ahead of yourself. By the sounds of it, this is your first game, so just don't worry about making all the classes yet. First things first: you've got a sprite moving around on the level, right? Now, implement yourself a menu. Assuming that when you press escape, the game pauses and you go to the menu, then pressing escape again brings you back into the game? Implement this (or whatever it is you want to have). Then worry about implementing other menus, multiple levels, etc..

here, I just want to visually explain what CI_Jolly already explained:

the following function is called every frame

each 'sprite' or 'object' class (you know - missiles, enemies, projectiles, player, etc..) does something every frame. A projectile moves a tiny bit every frame. A heat-seaking missile moves a bit, but also curves towards the player (I've got code that will do this, it involves 2D vectors - not too complicated).
An enemy follows some kind of AI function- (that's a complex subject, and I'm really inexperienced in that - you'll have to ask someone else for AI advice)
point is, everything is constantly DOING something.

I hope that clears things up for how to handle different gamestates. Anyways, once you've got that down, then you can worry about multiple levels. One thing at a time.

Here is a screenshot of my main menu.
Made it so that I can move up and down, and select with enter key. So far I only have "Start Game" active. When I press enter on it, it goes into the game (which is only a blue screen since no game has been added)



Now, just checking if this was done correctly:
I created a class called MainMenu which has the options of the menu (StartGame, Options, Intructions, HighScore), and also takes care of updating and drawing everything in that window.

What would be the next step of this process? I guess I have learned how to make the main menu, and any other menu.
Now maybe someone could help me out on how to start making the game. Like what classes to have (ei. sprite, animation, sound, etc), what each should do/behave, etc.