Hello, I am trying to make a simple shooter. However whenever I try to make it, so that you shoot a bullet, the bullet does not appear correctly, or it does not move. I'm using C++ and SDL2. I can post more code if it is needed.

	//Init values, X and Y and X_Vel and Y_Vel are declared as floats. 
gBullet.Img = IMG_Load("bullet.png");
	gBullet.Tex = SDL_CreateTextureFromSurface(GameRen, gBullet.Img);
	//gBullet.X = 0.0f;
	gBullet.Y = gPlayer.Y;
	//gBullet.X_Vel = 0.0f;
	gBullet.Y_Vel = 0.0f;
	gBullet.Width = 32;
	gBullet.Height = 32;
	gBullet.isAlive = false;
	//gBullet.Rect.x = (int)gBullet.X;
	gBullet.Rect.y = (int)gBullet.Y;
	gBullet.Rect.w = gBullet.Width;
	gBullet.Rect.h = gBullet.Height;
	gBullet.Timer = 0.05f;

//Supposed to fire bullet when space is pressed
if (event.key.keysym.sym == SDLK_SPACE)
				{
					gBullet.isAlive = true;
					gBullet.Y_Vel = 0.05f;
					gBullet.Y -= gBullet.Y_Vel;
					gBullet.Rect.y = (int)gBullet.Y;
				}

//Draw bullet	
if (gBullet.isAlive)
	{
		SDL_RenderCopy(GameRen, gBullet.Tex, NULL, &gBullet.Rect);
	}

The game is meant to be a vertical shooter, so I don't think I need to mess with the X coord. It is 2D. The player does move.

int ThisTime,LastTime;
float DeltaTime;

struct BULLET
{
    SDL_Surface* Img;
    SDL_Texture* Tex;
    SDL_Rect Rect;

    bool isAlive;
    float X, Y;
    float X_Vel, Y_Vel;
    int Width, Height;
    float Timer;
};

Here is the struct for the bullet.

    ThisTime = SDL_GetTicks();
    DeltaTime = (float)(ThisTime - LastTime) / MAX_TICKS;
    LastTime = ThisTime;

if (event.key.keysym.sym == SDLK_SPACE)
                {
                    gBullet.isAlive = true;
                    gBullet.Y_Vel = 0.05f;
                    gBullet.Y -= gBullet.Y_Vel * DeltaTime;
                    gBullet.Rect.y = (int)gBullet.Y;
                }
Here is some more code.

Try doing something like this:

if (event.key.keysym.sym == SDLK_SPACE)
                {
                    gBullet.isAlive = true;
                    gBullet.Y_Vel = 0.05f;
                    gBullet.Y -= gBullet.Y_Vel * DeltaTime;
                    gBullet.Rect.y = (int)gBullet.Y;
                    printf("gBullet.Rect.y = %d\ngBullet.Y = %f\nDeltaTime = %f\n", gBullet.Rect.y, gBullet.y, DeltaTime);
                }

Presumably, one of those three values isn't what you think it is. I can't tell at a glance what the problem is, but that should illuminate what it is pretty quickly (and kill your framerate, so don't keep it around of course).

if (event.key.keysym.sym == SDLK_SPACE)
{
    gBullet.isAlive = true;
    gBullet.Y_Vel = 0.05f;                  // (2)
    gBullet.Y -= gBullet.Y_Vel * DeltaTime; // (1)
    gBullet.Rect.y = (int)gBullet.Y;
}

// Update time
ThisTime = SDL_GetTicks();
DeltaTime = (float)(ThisTime - LastTime) / MAX_TICKS;
LastTime = ThisTime;

// Process events
SDL_Event ev;
while ( SDL_GetEvent(&ev) )
{
    // ...

    if (event.key.keysym.sym == SDLK_SPACE)
    {
        gBullet.isAlive = true;
        gBullet.Y_Vel = 300.0f;  // pixels per second
    }
}

// Update entities
if ( gBullet.isAlive )
{
    gBullet.Y -= gBullet.Y_Vel * DeltaTime;  
    gBullet.Rect.y = (int)gBullet.Y;
}    

Thanks, I got it. Here is the updated code.

	if (event.key.keysym.sym == SDLK_SPACE)
				{
					gBullet.isAlive = true;
					gBullet.Y_Vel = 25.0f;
					gBullet.Timer = 50.0f;
				}
			}
		}

		if (gBullet.isAlive)
		{
			gBullet.Timer--;
			gBullet.Y -= gBullet.Y_Vel * DeltaTime;
			gBullet.Rect.y = (int)gBullet.Y;

			if (gBullet.Timer == 0)
			{
				gBullet.isAlive = false;
				gBullet.Y = gPlayer.Y;
			}
		}

Now I just need to make it so that the bullet fires from the player and not from the left side of the screen.