Question

I’m having trouble generating two independent random sequences using the rand and srand functions. The details are below, any help would be most appreciated.

I’m working on a puzzle game for the iPhone, and usually for the random number generation I use the arc4 function. However for the multiplayer mode I want both players to have the same pieces throughout the game, and the only way I can control it is to have two repeatable random sequences. If I then send the seeds to the other device, the games will be identical. However when I use rand and srand and try to switch to the other seed, the sequence starts from scratch, I somehow have to initialize two independent sequences generated with a seed.

Thank you for your responses

Answer 1

Thank you for the suggestions, this is how I implemented the whole thing. I created a singleton class with 2 instance variables – seed1 and seed2 – anytime I want to get a number from the first generator I use the method generator1, same for generator2 method. The seed1/2 is instantly set to a newly generated number every time so I can just continue where I left off. In conlusion, Josh Caswell gave me all the information I needed. Check out the code if you ever need something like this. The object inits with seeds 1 and 1 but during the game they get replaced with some other numbers that both devices share.

@implementation RandomNumberGenerator

@synthesize seed1,seed2;

static RandomNumberGenerator *sharedGenerator = nil;

+(RandomNumberGenerator *) sharedInstance
{
if(!sharedGenerator) {
    sharedGenerator = [[RandomNumberGenerator alloc] initWithSeed1:1 andSeed2:1];
}

return sharedGenerator;
}

-(id) initWithSeed1:(int) seedOne andSeed2:(int) seedTwo{
self = [super init];
if (self)
{
    seed1 = seedOne;
    seed2 = seedTwo;
}
return self;
}

-(int) generator1{
srand(seed1);
int j = rand();
seed1 = j;
return abs(j);

}

-(int) generator2 {
srand(seed2);
int k = rand();
seed2 = k;
return abs(k);
}

-(int) giveRandom {
//return abs(arc4random());
return abs(arc4random());
}


@end