Bouncing ball

[nukes]

I am trying to make a program that will display a ball bouncing up and down with gravity also having an effect. It doesn't work right. Could one of you try it and see if you can improve it at all. You will need a 64x64 BMP file of something to bounce.

/* These header files are needed */
#include "SDL/SDL.h"
#include "stdio.h"
#include "stdlib.h"

int main() 
{
   SDL_Surface *screen;
   SDL_Surface *image;
   SDL_Rect rect, dest;
   int x,y, yvel, xvel, gravity, count, gcount;
  /* Initialise the video subsytem       */
  /* If it returns a non-null value, die */
   if (SDL_Init(SDL_INIT_VIDEO) != 0)
    { 
      printf("Unable to initialise SDL: %s\n",SDL_GetError());
      return 1;
    }

/* Make sure the program exits cleanly */
atexit(SDL_Quit);

/* Set 800x600 windowed mode */
screen = SDL_SetVideoMode(800,600,16,0);
if (screen==NULL) {
printf("Unable to set video mode: %s\n",SDL_GetError());
return 1;}

x = 5;
y = 5;
yvel = -2;
xvel = 2;
gravity = 2;
rect.x = 0;
rect.y = 0;
rect.w = 64;
rect.h = 64;
dest.x = 0;
dest.y = 0;
dest.w = 64;
dest.h = 64;
image = SDL_LoadBMP("ball.bmp");
for(gcount=0;gcount<200;gcount++) {
for(count=0;count<5;count++) {
if (x+xvel > 576) {
		    xvel = 0-(xvel/2);
		    x=576; 
		    printf("bounce"); }
if (y+yvel > 416) {
		    yvel = 0-(yvel/2);
		    y=416;
		    printf("bounce");}
if (x+xvel <0) {
		    xvel = 0-xvel;
		    x=0; 
		    printf("bounce");}
if (y+yvel < 0) {
		    yvel = 0;
		    y=0;
		    printf("bounce"); }		    
x+=xvel;
y+=yvel;
dest.x=(int)x;
dest.y=(int)y;
SDL_BlitSurface(image,&rect,screen,&dest);
SDL_UpdateRect(screen,0,0,0,0);
}
yvel+=gravity;
}
SDL_Delay(3000);
/***************************************/
/**    SDL Graphics init complete     **/
/***************************************/
printf("Graphics subsystem initialised\n");

printf("Quitting...\n");
return 0; }

This is my first attempt at programming anything in C for like 2 years, so go easy on me. It uses SDL, as you can see and I built it ok using G++ on my Linux system.

[nukes]

Ok, I've got that sorted a bit, I've still got some work to do, but I'll worry about that later.
Now I'm trying to get the ball to accelerate towards the mouse when the button is pressed. Any ideas? I had it in my head but can't remember how I was planing to do it. Here's what I've got now:

/* These header files are needed */
#include "SDL/SDL.h"
#include "stdio.h"
#include "stdlib.h"

int main() 
{
   SDL_Surface *screen;
   SDL_Surface *image;
   SDL_Surface *mouse;
   SDL_Rect rect, dest;
   int x,y, yvel, xvel, gravity, count, gcount, mousex, mousey, tangent;
   Uint8 buttons;
  /* Initialise the video subsytem       */
  /* If it returns a non-null value, die */
   if (SDL_Init(SDL_INIT_VIDEO) != 0)
    { 
      printf("Unable to initialise SDL: %s\n",SDL_GetError());
      return 1;
    }

/* Make sure the program exits cleanly */
atexit(SDL_Quit);

/* Set 800x600 windowed mode */
screen = SDL_SetVideoMode(800,600,16,0);
if (screen==NULL) {
printf("Unable to set video mode: %s\n",SDL_GetError());
return 1;}

x = 5;
y = 5;
yvel = 0;
xvel = 5;
gravity = 3;
rect.x = 0;
rect.y = 0;
rect.w = 78;
rect.h = 78;
dest.x = 0;
dest.y = 0;
dest.w = 64;
dest.h = 64;
image = SDL_LoadBMP("ball.bmp");
mouse = SDL_LoadBMP("pointer.bmp");
for(gcount=0;gcount<200;gcount++) {
for(count=0;count<5;count++) {
if (x+xvel > (800-78)) {
		    xvel = 3-(xvel);
		    x=(800-78); 
		    printf("bounce"); }
if (y+yvel > (600-78)) {
		    yvel = 0-(yvel-3);
		    y=(600-78);
		    printf("bounce");}
if (x+xvel <0) {
		    xvel = 3-xvel;
		    x=0; 
		    printf("bounce");}
if (y+yvel < 0) {
		    yvel = 0;
		    y=0;
		    printf("bounce"); }		    
x+=xvel;
y+=yvel;
dest.x=(int)x;
dest.y=(int)y;
SDL_PumpEvents();
buttons = SDL_GetMouseState(&mousex,&mousey);
// I've forgotten how I was going to do this.
//if(buttons && SDL_BUTTONS(1) != NULL) {
//	tangent = (mousey-y)/(mousex-x);
//	
//	} 
rect.w = 78;
rect.h = 78;
SDL_BlitSurface(image,&rect,screen,&dest);
dest.x=mousex;
dest.y=mousey;
rect.w=50;
rect.h=50;
SDL_BlitSurface(mouse,&rect,screen,&dest);
SDL_UpdateRect(screen,0,0,0,0);
}
yvel+=gravity;
}
SDL_Delay(3000);
/***************************************/
/**    SDL Graphics init complete     **/
/***************************************/
printf("Graphics subsystem initialised\n");

printf("Quitting...\n");
return 0; }

EDIT::
====
Doen't matter, I got it sorted, using dy=v*sin(theta) and dx=v*sin(theta) for working out the acceleration, where V is the standard acceleration I want, and theta is the angle between the position of the mouse and that of the ball from the horizontal.