xangle <> 0

Hi!
How do I prevent my xangle variable from equaling 0.....

Here is some of my code:

PHP Code:

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int Game_Main(void *parms)
{

// check of user is trying to exit
if (KEY_DOWN(VK_ESCAPE))
    PostMessage(main_window_handle, WM_DESTROY,0,0);
// Move paddle left
if (KEY_DOWN(VK_LEFT)) {
    lkpress = true;
    if (paddle.x >5) {
        paddle.x = paddle.x -4;
        Move_BOB(&paddle);
    }
} else if(KEY_DOWN(VK_RIGHT)) {        // Move paddle right
    rkpress = true;
    if(paddle.x + paddle.width  < SCREEN_WIDTH) {
        paddle.x = paddle.x +4;
        Move_BOB(&paddle);
        
    }
}

// start the timing clock
Start_Clock();

// clear the drawing surface
DD_Fill_Surface(lpddsback, 0);

Draw_BOB(&paddle,lpddsback);
Draw_BOB(&ball,lpddsback);
for (int draw = 0; draw<28; draw++)
Draw_BOB(&box[draw],lpddsback);

ball.xv = xangle;
ball.yv = yangle;
Move_BOB(&ball);

//the ball is going outside the screen
if(ball.x <= 0) {
    lasthit = LAST_HIT_LEFT;
    xangle = -xangle;
}
if( ball.x >= SCREEN_WIDTH - ball.width ){
    lasthit = LAST_HIT_RIGHT;
    xangle = -xangle;
}

// the ball is going outside the screen
if(ball.y <= 0) {
    lasthit = LAST_HIT_TOP;
    
        yangle = -yangle;
    
    if(xangle <0){
        xangle = xangle;
    }
    if(xangle > 0){
        xangle = -xangle;
    }
}

if(ball.y > SCREEN_HEIGHT){
    
    yangle = -yangle;
}
// the ball has hit the paddle
if(Collision_BOBS(&ball,&paddle)){
    yangle=-yangle; // change direction
    lasthit = LAST_HIT_BOTTOM;
        
    // This collision detection determine where the ball hits the paddle and 
    // calculates a new direction

    if(ball.x == paddle.x && ball.y == paddle.height){
        if(lkpress){
            if(xangle > 0){
                xangle = -3.5;
                lkpress =false;
            }
            else if(xangle <0){
                xangle = 3.5;
                lkpress = false;
            }
        }
    }
        if(ball.x > paddle.x && paddle.x <=19){
            if(xangle >0){
            xangle = 2;
            }
            else if(xangle <0){
                xangle = -2;
            }
        
        }
        
        if(ball.x > paddle.x +19 && paddle.x <=38){
            if(xangle > 0){
            xangle = 1;
            }
            else if(xangle <0){
                xangle = -1;
            }
        }
        if(ball.x >= paddle.x +38 && paddle.x <=57){
            if(xangle > 0){
            xangle = 0.5;
            }
            else if(xangle < 0){
                xangle = -0.5;
            }
        }

        if(ball.x > paddle.x +57 && paddle.x <=76){
            if(xangle < 0){
            xangle = -0.5;
            }
            else if(xangle > 0){
                xangle = 0.5;
            }

        }
        if(ball.x > paddle.x +76 && paddle.x <=95){
            if(xangle <0){
            xangle =-1;
            }
            else if(xangle >0){
                xangle = 1;
            }

        }
        if(ball.x > paddle.x +95 && paddle.x <115){
            
            if(xangle <0){
            xangle = -2;
            }
            else if(xangle >0){
                xangle = 2;
            }
        }
        
        if(ball.x == paddle.x + paddle.width  && ball.y == paddle.height){
        if(rkpress){
            if(xangle < 0){
                xangle = -3.5;
                rkpress = false;
            }
            else if(xangle >0){
                xangle = 3.5;
                rkpress = false;
            }
        }
    }
        

}






// flip the surfaces
DD_Flip();


// sync to 10ish fps
Wait_Clock(10);

// Perform collision detection with the blocks
for(counter = 0; counter<28; counter++)
if(Collision_BOBS(&ball,&box[counter])){
    if(xangle < 0){
        xangle = xangle;
        
        
    }
    if(xangle > 0){
        xangle = -xangle;
        
    }
    if(xangle ==0){
        if(lasthit == LAST_HIT_LEFT){
            xangle=+rand()%2;
        }
        if(lasthit == LAST_HIT_RIGHT){
            xangle=-rand()%-2;
        }
    }

    if(yangle < 0){
        yangle = -yangle;
    }
    if(yangle > 0){
        yangle = yangle;
    }
}
    
// return success
return(1);

} // end Game_Main 


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Quote:

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if(xangle ==0){
if(lasthit == LAST_HIT_LEFT){
xangle=+rand()%2;
}
if(lasthit == LAST_HIT_RIGHT){
xangle=-rand()%-2;
}
}

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I don't know what your program does, but this doesn't prevent it...

Quote:

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yangle = yangle

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things like this doesn't do anything either...

Quote:

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xangle=-rand()%-2

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Now this really confuses me. What sense does it make to calculate modulo a negative number?

I take it that if xangle == 0 - you want to change it to be non-zero..?

If this is the case you need to not use the rand() functions - it could return you zero - which would put you in the same situation. You're getting something like rand() % 2 - which could give you 0 or 1 (I think thats how mod works in C).

As kedaman says - the xangle = xangle etc lines could just be omitted - it's unnecessary.

Other than that - theres too much code for me to wade through to find anything else - and I should be working :rolleyes: . (Sorry, but it's true).

HD

Quote:

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(I think thats how mod works in C).

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Not only in C but everywhere. Modulo is a basic algebraic operation. It means "do an integer division and return the remainder". Which can be anything from 0 to divisor-1.

Unfortunately while the theory is true - implementations of mod can vary (or so I was told by my Cryptography lecturer at University a couple of years ago).

Apparently while the modulo theory says 0 - (n-1), the implementations of it can mean 1 - n.

Newer languages have a consistent implementation, but some systems differ.

If this is wrong I would be happy to go back to university to complain to the lecturer :D )

HD

Quote:

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Originally posted by HairyDave
Apparently while the modulo theory says 0 - (n-1), the implementations of it can mean 1 - n.

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This is dead wrong, and makes no sense. It essentially says that for any division, you cannot have a remainder of 0, but you can have a remainder of n, which, of course is incorrect. If there are implementations of that operation that behave like that... well, its just wrong.

Z.

Code:

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if(xangle > 0){
        xangle = -xangle;
        if(xangle< 0)
            xangle=0;
}

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