making alot of the same thing

[poonninja]

i need to make more than one thing of the same thing. that thing is a ball. so when the user presses space bar it makes a new ball on the screen. i think i can do this with a set of classes maybe. thanks for the help.

[Disch]

class Ball
{
 // ...
};

// somewhere
std::vector< Ball >  myballs;  // array of balls

// called when space is pressed
void AddBall()
{
  myballs.push_back( Ball() );
}

Note it's probably not most efficient to store the Ball in the vector as per the above example. A better alternative might be to use a std::deque instead so there's less chance of a bulk copy. Or dynamically allocate the balls with new (although that makes cleanup more difficult).

[poonninja]

whats the difference between deque and a vector? thanks for the help.

[Disch]

Relevent topics:
http://cplusplus.com/reference/stl/deque/

http://cplusplus.com/reference/stl/vector/


Quote of interest:

Both vectors and deques provide thus a very similar interface and can be used for similar purposes, but internally both work in quite different ways: While vectors are very similar to a plain array that grows by reallocating all of its elements in a unique block when its capacity is exhausted, the elements of a deques can be divided in several chunks of storage, with the class keeping all this information and providing a uniform access to the elements. Therefore, deques are a little more complex internally, but this generally allows them to grow more efficiently than the vectors with their capacity managed automatically, specially in large sequences, because massive reallocations are avoided.

[poonninja]

thanks again. one last thing how would i change the first balls info without changing the rest?

example:

class Ball
{
    float positionx;
    float positiony;
    float positionz;
};

vector<Ball>ball;

add()
{
   Ball.positionx = random;
   Ball.Push_back(Ball());
}

sorry if im being a bit annoying. thanks for the help.

[Disch]

vector<Ball> balls;

void func()
{
  // add 3 balls
  balls.push_back( Ball() );
  balls.push_back( Ball() );
  balls.push_back( Ball() );

  // change the 2nd one so it's at 1,2,3
  balls[1].positionx = 1;
  balls[1].positiony = 2;
  balls[1].positionz = 3;
}

[poonninja]

thank you! :)

edit :

when i run that balls[1].positionx = 1; it randomly closes. i am sure its this part because i commented it out and the program exicuted fine. this is the exact code.

balls[numballs].position[0]0;
balls[numballs].position[1]0;
balls[numballs].position[2]0;
balls[numballs].radius = 0.5f;

can any one please tell me how i can fix

[Disch]

I'm guessing you're stepping out of bounds in your array. Don't do balls[1] unless you have at least 2 balls in the vector. If you have less than 2, you're overflowing the buffer (bad!)

also I don't see how this would compile:

balls[numballs].position[0]0;
balls[numballs].position[1]0;
balls[numballs].position[2]0;

?

[poonninja]

ha sorry i increased the number of balls before i changed everything. lol