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## Random number problem!

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### #1iwoplaza  Members

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Posted 19 June 2012 - 08:53 AM

I'm making three-dimensional application in OpenGL, which generates a random blocks in the world (something like Minecraft). This is my script to generate blocks:

void GenBlocks(){
int currblock;
int currXline;
int currZline;
int randID;
for(currblock = 0,currXline = 1,currZline = 1;currblock < blockAM;currblock++,currXline++){
randID = rand() % 2 + 1;
if(currXline > pierw(blockAM)){
currXline = 1;
currZline++;
}
block[currblock].x = currXline*3;
block[currblock].y = 0;
block[currblock].z = currZline*3;
block[currblock].id = randID;
}
}


But every time when I run the application, it generates the same!

### #2fastcall22  Moderators

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Posted 19 June 2012 - 09:21 AM

You need to seed the random number generator when the program starts.
zlib: eJzVVLsSAiEQ6/1qCwoK i7PxA/2S2zMOZljYB1TO ZG7OhUtiduH9egZQCJH9 KcJyo4Wq9t0/RXkKmjx+ cgU4FIMWHhKCU+o/Nx2R LEPgQWLtnfcErbiEl0u4 0UrMghhZewgYcptoEF42 YMj+Z1kg+bVvqxhyo17h nUf+h4b2W4bR4XO01TJ7 qFNzA7jjbxyL71Avh6Tv odnFk4hnxxAf4w6496Kd OgH7/RxC

### #3szecs  Members

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Posted 19 June 2012 - 09:24 AM

Random number generators aren't really random.
That means they use some calculations, pre-defined arrays of pseudo-random numbers, whatever, you get the idea.
Every random number generators have a "randomize" function of some sorts, for example "srand". They take an initial value, often called as "seed". Using he same seed value will produce exactly the same sequence of numbers. If you don't call this initial srand, the generator will use a default seed I guess.

So, you need to call srand and pass a number to it. You would probably ask what can you use as seed, if you can't use a really random number in the first place.
Usually, system time is used for that, since it's in milliseconds and ever growing.
(what's cool about this thing is that if you save then load the seed number, you can regenerate exactly the same world from only an int. As you have it now.)

I'm ninja'd.

Edited by szecs, 19 June 2012 - 09:28 AM.

### #4iwoplaza  Members

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Posted 19 June 2012 - 09:35 AM

Thanks .
P.S. Now I understand how are seeds in minecraft working .)

### #5alnite  Members

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Posted 19 June 2012 - 12:52 PM

### #6tanzanite7  Members

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Posted 20 June 2012 - 06:20 PM

Old topic!

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