2d Collision detection theory problem...

//Mark St. Jean//Brandon Walton//WASTEDink 2004//First online game alpha 1.0// EDITED// Name: John Sedlak// December 20, 2004// Main edits://  Made map global.//  Made key function work with collision detection//  Added some theoretical class ideas at bottom, commented out#include <iostream>#include <stdlib.h>#include <winsock2.h>#include <SDL/SDL.h> // EDITED: Made globalint map [10][19]= {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,                    0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,                    0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,                    0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,                    0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,                    0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,                    0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,                    0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,                    0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,                    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};//Functionsvoid host();void join();void drawMap();void drawScene();//draws bitmaps, x = o is top, y = 0 is left, sprite is the imagevoid draw(int x, int y, SDL_Surface *sprite, SDL_Surface *screen);        //Globals    //Main screen    SDL_Surface *titleScreen;    SDL_Surface *gameScreen;    //Tile Surfaces    SDL_Surface *tile1 = SDL_LoadBMP("gfx/tiles/tile1.bmp");    SDL_Surface *tile2 = SDL_LoadBMP("gfx/tiles/tile2.bmp");   //Sprites    SDL_Surface *sprite1 = SDL_LoadBMP("gfx/sprites/sprite1.bmp");    //Sprite coordniates    int xpos = 40;    int ypos = 320;using namespace std;  int main(int argc, char *argv[]){    Uint8* keys;       //Surfaces used in SDL    SDL_Surface *title1;    SDL_Surface *title2;    SDL_Surface *title3;    //Initalize Graphics    title1 = SDL_LoadBMP("gfx/title1.bmp");    title2 = SDL_LoadBMP("gfx/title2.bmp");    title3 = SDL_LoadBMP("gfx/title3.bmp");    //Sets transparency    SDL_SetColorKey(sprite1, SDL_SRCCOLORKEY, SDL_MapRGB(sprite1->format, 255, 100, 255));        //boolean used to determine if the game is running    bool isRunning;    //A SDL event, used to keep gamerunning.    SDL_Event event;    //unload function    atexit(SDL_Quit);        //sets the video mode that SDL uses    // Peremiters are window width, window height,color depth, then flags    titleScreen = SDL_SetVideoMode(760, 400, 0, SDL_HWSURFACE|SDL_DOUBLEBUF);    //gives the boolean a value    isRunning = true;    drawMap();    int i_x, i_y;        //Main game loop    while(isRunning == true)    {        // Setup the indexing for collision detection        i_x = ypos / 40;        i_y = xpos / 40;        //Poll event         SDL_PollEvent(&event);        //event that ends SDL and main game loop       if(event.type == SDL_KEYDOWN)        {            if(event.key.keysym.sym == SDLK_ESCAPE)                isRunning = false;        }        keys = SDL_GetKeyState(NULL);       if ( keys[SDLK_UP] )       {           // If the tile above the player is walkable...           if(map[i_x][i_y - 1] == 1)           {               // Subtract his yposition               ypos--;           }           else           {               // If it isn't the player might not be as close               //   as the tile since we are subtracting by pixels.               //   This takes care               if(ypos > i_y * 40 + 40)                   ypos--;           }          /*if (ypos -1 == notWalkable)          ypos -= 0;          else          ypos = 1; */       }       if ( keys[SDLK_DOWN] )        {           // Same as before, just adjusted for the down key...           if(map[i_x][i_y + 1] == 0)           {               ypos++;           }           else           {               if(ypos < i_y * 40 + 40)                   ypos++;           }       }       if ( keys[SDLK_LEFT] )        {           if(map[i_x - 1][i_y] == 1)           {               xpos--;           }           else           {               if(xpos > i_x * 40)                   xpos--;           }       }       if ( keys[SDLK_RIGHT] )              {           if(map[i_x + 1][i_y] == 0)           {               xpos++;           }           else           {               if(xpos < i_x * 40)                   xpos++;           }          /*if (xpos +1 == notWalkable)          xpos += 0;          else          xpos += 1; */       }       drawScene();    }    cout << "WELCOME 3 DA GAME!!! Well its actuially not here yet..." << endl;  cout << "This just tests the connection :)" << endl;    if (event.type == SDL_QUIT)       {              SDL_FreeSurface(title1);              SDL_FreeSurface(title2);              SDL_FreeSurface(title3);              isRunning = false;       }      return 0;}//SDL code---------------------------------------------//Draws stuff to the screenvoid draw(int x, int y, SDL_Surface *sprite, SDL_Surface *screen){    SDL_Rect source;    SDL_Rect dest;    source.x = 0;    source.y = 0;    source.w = sprite->w;    source.h = sprite->h;    dest.x = x;    dest.y = y;    dest.w = source.w;    dest.h = source.h;    SDL_BlitSurface(sprite, &source, screen, &dest);    return;}//DRAWS MAP!!!void drawMap(){   int map [10][19]= {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,                    0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,                    0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,                    0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,                    0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,                    0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,                    0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,                    0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,                    0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,                    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};for(int y = 0;y < 10; y++){     for(int x = 0;x < 19; x++)    {        if(map[y][x] == 1)         {           draw(x*40,y*40,tile1,titleScreen);         }        else if (map[y][x] == 0)         {           draw(x*40,y*40,tile2,titleScreen);         }    }}}//draws backgroundvoid drawScene(){  drawMap();  draw(xpos, ypos, sprite1, titleScreen);  SDL_Flip(titleScreen);}//Network Code-------------------------------------------------//~~~~~~~~~~~~~~~~~~~~~~~~//~~~~~~~~~~~~~~~~~~~~~~~~//~~~~~~~~~~~~~~~~~~~~~~~~//Hosts the game//~~~~~~~~~~~~~~~~~~~~~~~~//~~~~~~~~~~~~~~~~~~~~~~~~//~~~~~~~~~~~~~~~~~~~~~~~~void host(){  int error;  //loads winsock  WSADATA wsaData;  error = WSAStartup(MAKEWORD(2, 0), &wsaData);    //error handler  if (error != 0)  {    cout << "Couldn't Initialize Winsock: 1" << endl;  // unload WinSock  WSACleanup ();  return;  }    cout << "Winsock initialized..." << endl;    //creates a socket  SOCKET connectSocket;  connectSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);    //error handler  if (connectSocket == INVALID_SOCKET)  {    cout << "Couldnt create socket: 2" << endl;  // unload WinSock  WSACleanup ();  return;   }    cout << "Socket created..." << endl;    //This is the port it connects to, we are using 12521  const int port = 12521;   // the address structure for a TCP socket  sockaddr_in addr;  addr.sin_family = AF_INET;      // Address family Internet  addr.sin_port = htons (port);   // Assign port to this socket  addr.sin_addr.s_addr = htonl (INADDR_ANY);   // No destination    if (bind(connectSocket, (LPSOCKADDR)&addr, sizeof(struct sockaddr)) == SOCKET_ERROR)  {   cout << "Couldn't bind socket: 3" << endl;  // unload WinSock  WSACleanup ();  return;  }    cout << "Socket binded..." << endl;    //Waits for the connection   cout << "Waiting for connection from other player..." << endl;  listen(connectSocket, 1);    //Socket for connection  SOCKET connectPlayer;    connectPlayer = accept(connectSocket, NULL, NULL);  cout << "Client accepted... SUCCESS!" << endl;    closesocket(connectPlayer);}  //~~~~~~~~~~~~~~~~~~~~~~~~//~~~~~~~~~~~~~~~~~~~~~~~~//~~~~~~~~~~~~~~~~~~~~~~~~//Joins the host//~~~~~~~~~~~~~~~~~~~~~~~~//~~~~~~~~~~~~~~~~~~~~~~~~//~~~~~~~~~~~~~~~~~~~~~~~~void join(){  int error;  string ipAddress;     cout << "Please enter in the hosts IP address: ";  cin >> ipAddress;    //loads winsock  WSADATA wsaData;  error = WSAStartup(MAKEWORD(2, 0), &wsaData);    //error handler  if (error != 0)  {    cout << "Couldn't Initialize Winsock: 1" << endl;    // unload WinSock    WSACleanup ();    return;  }    cout << "Winsock initialized..." << endl;    //Stores information about the hosting player  LPHOSTENT hostEntry;  in_addr iaHost;  //Hosts IP address  iaHost.s_addr = inet_addr(ipAddress.c_str());  //Gathers information using the IP address  hostEntry = gethostbyaddr((const char *)&iaHost, sizeof(struct in_addr), AF_INET);  //error handling  if (!hostEntry)  {     cout << "Error gathering data..." << endl;    WSACleanup ();    return;  }          //Creates socket  SOCKET connectSocket;  connectSocket = socket(AF_INET, SOCK_STREAM,IPPROTO_TCP);    //error handler  if (connectSocket == INVALID_SOCKET)  {    cout << "Couldnt create socket: 2" << endl;  // unload WinSock  WSACleanup ();  return;  }    cout << "Socket created..." << endl;    //This is the port it connects to, we are using 12521  const int port = 12521;   // the address structure for a TCP socket  sockaddr_in serverInfo;  // Address family Internet  serverInfo.sin_family = AF_INET;    serverInfo.sin_port = htons (port);   // Assign port to this socket    serverInfo.sin_addr = *((LPIN_ADDR)*hostEntry->h_addr_list);   // Hosts IP address      //Connects to the host  error = connect(connectSocket,(LPSOCKADDR)&serverInfo,sizeof(struct sockaddr));    //error handler  if (error != 0)  {   cout << "Couldn't connect to host: 3" << endl;  // unload WinSock  WSACleanup ();  return;  }    cout << "Connected" << endl;  }

typedef struct point_struct{    Sint16        x;    Sint16        y;}POINT;typedef struct tile_struct{    Uint32        tile_id;    SDL_Rect      source_rect;    SDL_Rect      collision_rect;    SDL_Surface   *source_surface;    Uint32        movement_flags;    // etc....}TILE;typedef struct sprite_struct{    Uint32        sprite_id;    SDL_Rect      source_rect;    SDL_Rect      collision_rect;    SDL_Surface   source_surface;    POINT         world_position;    POINT         anchor_point;    // etc...}SPRITE;