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for loop warnings, help request

AmbitiousCoder (27)

Hi guys,


I've got my code in progress. It compiles fine, runs fine, no problems whatsoever; however, when I compile it, it returns a warning: 

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#include <SDL.h>
using namespace std;


class Cube{
public:
    Cube(int x,int y,int w,int h) { XPos = x; YPos = y; width = w; height = h; box.x = XPos; box.y = YPos; box.w = width; box.h = height;}
    SDL_Rect box;

private:
    int XPos;
    int YPos;
    int width;
    int height;
};

class Enemy{
public:
    Enemy(int x,int y) { xPos = x; yPos = y; width = 50; height = 15; box.x = xPos; box.y = yPos; box.w = width; box.h = height;}
    SDL_Rect box;

private:
    int xPos;
    int yPos;
    int width;
    int height;
};

//------------------------------COLLISION DETECTION-----------------------------------//

//bool collision(SDL_Rect* rec1, SDL_Rect* rec2)
//{
//    if(rec1->y >= rec2->y + rec2->h)
//    {
//        return false;
//    }
//    if(rec1->y + rec1->h <= rec2->y)
//    {
//        return false;
//    }
//    if(rec1->x >= rec2->x + rec2->w)
//    {
//        return false;
//    }
//    if(rec1->x + rec1->w <= rec2->x)
//    {
//        return false;
//    }
//    return true;
//}

//------------------------------------------------------------------------------------//

int main(int argc, char* argv[])
{
    SDL_Init(SDL_INIT_EVERYTHING);
    SDL_Surface *screen, *ship, *enemy, *bullet;
    screen = SDL_SetVideoMode(640,480,32,SDL_SWSURFACE);
    ship = SDL_DisplayFormat(SDL_LoadBMP("ship1.bmp"));
    SDL_SetColorKey(ship, SDL_SRCCOLORKEY, SDL_MapRGB(screen->format, 0xff, 0xff, 0xff));
    enemy = SDL_DisplayFormat(SDL_LoadBMP("enemy.bmp"));
    SDL_SetColorKey(enemy, SDL_SRCCOLORKEY, SDL_MapRGB(screen->format, 0xff, 0xff, 0xff));
    bullet = SDL_DisplayFormat(SDL_LoadBMP("bullet.bmp"));
    SDL_SetColorKey(bullet, SDL_SRCCOLORKEY, SDL_MapRGB(screen->format, 0xff, 0xff, 0xff));
    bool running = true;
    bool b[2] = {0,0};
    Uint32 start;
    int unsigned second = 1000;
    int unsigned fps = 60;
    SDL_Event event;
    Uint32 black = SDL_MapRGB(screen->format,0,0,0);
    Cube * Box = new Cube(125,450,65,15);
    int unsigned paddleVel = 3;
    int unsigned i = 0;
    int unsigned k = 6;
    int unsigned enemyX = 80;
    int unsigned enemyY = 30;
    int unsigned const opponents = 24;
    Enemy * opponent[opponents];
    for(int unsigned row = 0; row < (opponents / 6); row++ )
    {
        for( i; i < k; i++ )
        {
           opponent[i] = new Enemy(enemyX,enemyY);
           enemyX = enemyX + 85;
        }
        enemyX = 80;
        enemyY += 30;
        k += 6;
    }
    while(running)
    {
            start = SDL_GetTicks();
            while(SDL_PollEvent(&event))
            {
                switch(event.type)
                {
                case SDL_QUIT:
                    running = false;
                    break;
                case SDL_KEYDOWN:
                    switch(event.key.keysym.sym)
                    {
                    case SDLK_ESCAPE:
                        running = false;
                        break;
                    case SDLK_LEFT:
                        b[0] = 1;
                        break;
                    case SDLK_RIGHT:
                        b[1] = 1;
                        break;
                    }
                break;
                case SDL_KEYUP:
                    switch(event.key.keysym.sym)
                    {
                    case SDLK_LEFT:
                        b[0] = 0;
                        break;
                    case SDLK_RIGHT:
                        b[1] = 0;
                        break;
                    }
                    break;
                }
            }
//--------------------------ENEMY MOVEMENT-----------------------------//

//--------------------------BULLET MOVEMENT----------------------------//

//--------------------------SHIP MOVEMENT------------------------------//
            if(b[0]){
                Box->box.x -= paddleVel;
                if(Box->box.x <= 0){
                        Box->box.x += paddleVel;
                }
            }
            if(b[1]){
                Box->box.x += paddleVel;
                if(Box->box.x + Box->box.w >= 640){
                        Box->box.x -= paddleVel;
                }
            }
//----------------------------RENDER-----------------------------------//
            SDL_FillRect(screen,&screen->clip_rect,black);
            SDL_BlitSurface(ship, NULL, screen, &Box->box);
            for(int unsigned j = 0; j < opponents; j++)
            {
                SDL_BlitSurface(enemy, NULL, screen, &opponent[j]->box);
            }
            SDL_Flip(screen);
            if(second/fps>(SDL_GetTicks()-start))
                SDL_Delay(second/fps-(SDL_GetTicks()-start));
    }
    SDL_FreeSurface(screen);
    SDL_FreeSurface(ship);
    SDL_FreeSurface(enemy);
    SDL_FreeSurface(bullet);
    SDL_Quit();
    return 0;
}


main.cpp|82|warning: statement has no effect [-Wunused-value]|

As you can see, line 82 returns with this warning. Like I said, nothing works other than intended, everything compiles, everything runs, no problems. Any ideas as to what the issue is, and what I can do to correct it? I assume it is probably something with the i int for the first argument, but I just don't know what to do with it. Any help is appreciated. Thanks!
Alrededor (166)
If you were to write something like
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2
 
   int n = 0;
   n;


The second line n; is perfectly legal C++. It evaluates n which is zero and then throws the result away.

On line 82: for( i; i < k; i++ )

The variable i was initialized to zero earlier outside of the loop on line 74. Consequently, the i; part of
for( i; i < k; i++ ) is evaluated to zero and the result thrown away. Replace the i; with a null statement.
Try changing line 82 to:

for( ; i < k; i++ )

and see if the warning goes away.
AmbitiousCoder (27)
That actually does it! Thanks! We learn something new every day. :)
AmbitiousCoder (27)

Hi again.

I've actually moved on, and have come across another issue. I've changed my code a bit, moving things out for global variables, adding an external function, etc:

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#include <SDL.h>
using namespace std;


class Cube{
public:
    Cube(int x,int y,int w,int h) { XPos = x; YPos = y; width = w; height = h; box.x = XPos; box.y = YPos; box.w = width; box.h = height;}
    SDL_Rect box;

private:
    int XPos;
    int YPos;
    int width;
    int height;
};

class Enemy{
public:
    Enemy(int x,int y) { xPos = x; yPos = y; width = 50; height = 15; box.x = xPos; box.y = yPos; box.w = width; box.h = height;}
    SDL_Rect box;

private:
    int xPos;
    int yPos;
    int width;
    int height;
};

//------------------------------COLLISION DETECTION-----------------------------------//

//bool collision(SDL_Rect* rec1, SDL_Rect* rec2)
//{
//    if(rec1->y >= rec2->y + rec2->h)
//    {
//        return false;
//    }
//    if(rec1->y + rec1->h <= rec2->y)
//    {
//        return false;
//    }
//    if(rec1->x >= rec2->x + rec2->w)
//    {
//        return false;
//    }
//    if(rec1->x + rec1->w <= rec2->x)
//    {
//        return false;
//    }
//    return true;
//}

//------------------------------------------------------------------------------------//

void arrayMove();
int unsigned const opponents = 24;
int unsigned tmpEnemyVel;
Enemy * opponent[opponents];
int unsigned const lastOpponent = (opponents - 1);

int main(int argc, char* argv[])
{
    SDL_Init(SDL_INIT_EVERYTHING);
    SDL_Surface *screen, *ship, *enemy, *bullet;
    screen = SDL_SetVideoMode(640,480,32,SDL_SWSURFACE);
    ship = SDL_DisplayFormat(SDL_LoadBMP("ship1.bmp"));
    SDL_SetColorKey(ship, SDL_SRCCOLORKEY, SDL_MapRGB(screen->format, 0xff, 0xff, 0xff));
    enemy = SDL_DisplayFormat(SDL_LoadBMP("enemy.bmp"));
    SDL_SetColorKey(enemy, SDL_SRCCOLORKEY, SDL_MapRGB(screen->format, 0xff, 0xff, 0xff));
    bullet = SDL_DisplayFormat(SDL_LoadBMP("bullet.bmp"));
    SDL_SetColorKey(bullet, SDL_SRCCOLORKEY, SDL_MapRGB(screen->format, 0xff, 0xff, 0xff));
    bool running = true;
    bool b[2] = {0,0};
    Uint32 start;
    int unsigned second = 1000;
    int unsigned fps = 60;
    SDL_Event event;
    Uint32 black = SDL_MapRGB(screen->format,0,0,0);
    Cube * Box = new Cube(125,450,65,15);
    int tmpTimer = fps;
    int enemyVel = 10;
    tmpEnemyVel = enemyVel;
    int unsigned paddleVel = 3;
    int unsigned i = 0;
    int unsigned k = 6;
    int unsigned enemyX = 80;
    int unsigned enemyY = 30;
    for(int unsigned row = 0; row < (opponents / 6); row++ )
    {
        for(; i < k; i++ )
        {
           opponent[i] = new Enemy(enemyX,enemyY);
           enemyX = enemyX + 85;
        }
        enemyX = 80;
        enemyY += 30;
        k += 6;
    }
    while(running)
    {
            start = SDL_GetTicks();
            while(SDL_PollEvent(&event))
            {
                switch(event.type)
                {
                case SDL_QUIT:
                    running = false;
                    break;
                case SDL_KEYDOWN:
                    switch(event.key.keysym.sym)
                    {
                    case SDLK_ESCAPE:
                        running = false;
                        break;
                    case SDLK_LEFT:
                        b[0] = 1;
                        break;
                    case SDLK_RIGHT:
                        b[1] = 1;
                        break;
                    }
                break;
                case SDL_KEYUP:
                    switch(event.key.keysym.sym)
                    {
                    case SDLK_LEFT:
                        b[0] = 0;
                        break;
                    case SDLK_RIGHT:
                        b[1] = 0;
                        break;
                    }
                    break;
                }
            }
//--------------------------ENEMY MOVEMENT-----------------------------//
            tmpTimer -= 3;
            if(tmpTimer == 0)
            {
                arrayMove();
                tmpTimer = fps;
            }

//--------------------------BULLET MOVEMENT----------------------------//

//--------------------------SHIP MOVEMENT------------------------------//
            if(b[0]){
                Box->box.x -= paddleVel;
            if(Box->box.x <= 0){
                Box->box.x += paddleVel;
                }
            }
            if(b[1]){
                Box->box.x += paddleVel;
            if(Box->box.x + Box->box.w >= 640){
                Box->box.x -= paddleVel;
                }
            }
//----------------------------RENDER-----------------------------------//
            SDL_FillRect(screen,&screen->clip_rect,black);
            SDL_BlitSurface(ship, NULL, screen, &Box->box);
            for(int unsigned j = 0; j < opponents; j++)
            {
                SDL_BlitSurface(enemy, NULL, screen, &opponent[j]->box);
            }
            SDL_Flip(screen);
            if(second/fps>(SDL_GetTicks()-start))
                SDL_Delay(second/fps-(SDL_GetTicks()-start));
    }
    SDL_FreeSurface(screen);
    SDL_FreeSurface(ship);
    SDL_FreeSurface(enemy);
    SDL_FreeSurface(bullet);
    SDL_Quit();
    return 0;
}

void arrayMove()
{
    for(int unsigned m = 0; m < opponents; m++)
    {
        opponent[m]->box.x -= tmpEnemyVel;
        if(opponent[m]->box.x <= 30)
                    tmpEnemyVel = (10 * -1);
        if(opponent[lastOpponent]->box.x + opponent[lastOpponent]->box.w >= 610)
                    tmpEnemyVel = 10;
    }
}


So basically, my array of opponents moves just fine as set by the tmpTimer.
It's the collision that I'm having an issue with. When the entire array gets to the x = 30 mark, the enemyVel reverses, so that the array starts moving the opposite direction. The problem is that opponent[0] moves one more step in the x-= direction before changing to the x+= direction. Only opponent[0] does this. Once the array reaches the other side of the screen, everything works fine. On it's way back left, the same thing happens. When the array reaches x = 30, the entire array except opponent[0] turns around and proceeds in the opposite direction. The very next tick, opponent[0] turns around, but of course is now 20 pixels to the left of the rest of the array...

After looking at this for about a half hour, I must be overlooking something. I need to walk away for a bite to eat, lol. Anyone willing to take a look for me? Help is so greatly appreciated. I know I seem to hit a lot of brick walls, and I'm glad this forum is so upfront to help. Thanks!
AmbitiousCoder (27)
Sorry guys. After getting a bite to eat, it gave me time to sit at the dinner table and think things over. I've figured out the problem. It seems in likes 181-185, the two if statements need to be made before the move command. I guess a sequential check, and it was incorrect. Thanks anyway for anyone who has looked this over! I'm sure I'll be back.
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