Ok so i am working on this program using PhysX and one of the samples that comes with the library has a while loop that runs in the rendercall back function. like so

int nbActors = gScene->getNbActors();
NxActor** actors = gScene->getActors();
while(nbActors--){

NxActor* actor = *actors++;

///render all the stuff with physics :)

}

What i dont understand is that while loop. whats going on there exactly. from what i would guess its like incrementing through the number of actors and running the loop for each one but im not sure. could some one explaine this use of a while loop and or perhaps the use of the decrementer as something being passed like that.

Thanks

so like is this loop is going to loop until nbActors-- reaches 0 before it breaks out?

also

If i wanted to specify a specific actor in that array " *actors++ " and start looping upwards from there how would that be done? for example if i wanted to start at index 5 and then ++ from there how would that be done?

Ok so i am working on this program using PhysX and one of the samples that comes with the library has a while loop that runs in the rendercall back function. like so

int nbActors = gScene->getNbActors();
NxActor** actors = gScene->getActors();
while(nbActors--){

NxActor* actor = *actors++;

///render all the stuff with physics

}

What i dont understand is that while loop. whats going on there exactly. from what i would guess its like incrementing through the number of actors and running the loop for each one but im not sure. could some one explaine this use of a while loop and or perhaps the use of the decrementer as something being passed like that.

That while-loop is an obfuscated way of writing this for-loop.

int nbActors = gScene->getNbActors();
for (int i = 0; i < nbActors; ++i)
{
    NxActor* actor = actors;
    // ...
}

the world is full of Klever Koders.

int nbActors = gScene->getNbActors();

NxActor** actors = gScene->getActors();


while(nbActors--){ // Line A

     NxActor* actor = *actors++; // Line B


    ///render all the stuff with physics

}

Line (A) exploits that non-zero integers evaluate to true, while zero evaluates to false. The while loop will count down from the number of actors (the 'x--' decrement operator returns the current value of x, and afterwards reduces the value of x by one), until the number is zero.

Line (B) exploits the fact that items in an array are allocated contiguously (i.e. one after another), to move a pointer through the array (the 'x++' increment operator is the opposite of decrement, it returns x and then increases the value of x by one).

So swiftcoder, thank you very much well written and that helped me indeed.

but in Line B if i wanted to start at index 4 of actors, then increment up from there, how would i write that?

I know its a simple answer I am just not understanding or thinking about it correctly.

while(nbActors--){ // Line A

     NxActor* actor = *actors++; // Line B


    ///render all the stuff with physics

}

// Like this

actors += 4;   // start from element 4 instead of 0
nbActors -= 4; // still got the same number though so reduce initial loop count

while(nbActors--){ // Line A

     NxActor* actor = *actors++; // Line B


    ///render all the stuff with physics

}

EDIT: You need to check that nbActors (after subtracting 4) is >= 1 before you enter the while loop bit though otherwise bad things will happen.

oh I am sorry, but i should have included that I am using the first 3 values in that array within that loop. so imagine if actors[0] - actors[4] are being used and passed to some other function or variable with in the loop. Then after I am wanting to take the rest of the actors in the array, actors[4] and upward, and increment upwards as in Line B.

How would I then increment upwards knowing i dont want to disturb actors 0-4 in the array?

for example:

while(nbActors--){ // Line A

    NxActor* actor0 = *actors[0]; 
    NxActor* actor1 = *actors[1]; 
    NxActor* actor2 = *actors[2]; 
    NxActor* actor3 = *actors[3]; 


     NxActor* actor = *actors++; // Line B     I want this line to up date every loop 
                                            // with new actors number counting upward from 4


    ///render all the stuff with physics

}

How would I then increment upwards knowing i dont want to disturb actors 0-4 in the array?

Like this:

NxActor* actor0 = actors[0];
NxActor* actor1 = actors[1];
NxActor* actor2 = actors[2];
NxActor* actor3 = actors[3];

actors += 4; // start from element 4 instead of 0
nbActors -= 4; // still got the same number though so reduce initial loop count

if(nbActors > 0)
{
    while(nbActors--){ // Line A
        NxActor* actor = *actors++; // Line B     

    ///render all the stuff with physics
    }
}

Alternatively:

NxActor* actor0 = *actors++;
NxActor* actor1 = *actors++;
NxActor* actor2 = *actors++;
NxActor* actor3 = *actors++;

nbActors -= 4; // still got the same number though so reduce initial loop count

if(nbActors > 0)
{
    while(nbActors--){ // Line A
        NxActor* actor = *actors++; // Line B

    ///render all the stuff with physics
    }
}