Randomize
Hehe this might be a little unclear, so I''ll explain:
Say you wanted to have a random number from 1 to 10.
First, you should seed the random number generator with something, preferably a time function, like timeGetTime(), or clock(), so it''s always different. Do this only once in the very beginning of your program.
Then, to get a random number, you would use the random function something like this:
rand()%10 would give you a random number from 1 to 10. (Or 0 to 9, I forget)
rand()%20 would give you ..... 1 to 20
if you want from other numbers than 0 or 1, you have to use math.
like if you want a number from 10 to 20, you should do something like
rand()%10 + 10;
get it? =D
-=Lohrno
Say you wanted to have a random number from 1 to 10.
First, you should seed the random number generator with something, preferably a time function, like timeGetTime(), or clock(), so it''s always different. Do this only once in the very beginning of your program.
Then, to get a random number, you would use the random function something like this:
rand()%10 would give you a random number from 1 to 10. (Or 0 to 9, I forget)
rand()%20 would give you ..... 1 to 20
if you want from other numbers than 0 or 1, you have to use math.
like if you want a number from 10 to 20, you should do something like
rand()%10 + 10;
get it? =D
-=Lohrno
Never use modulus with rand. Use division instead, or you''ll screw up even distribution:
int random_number = float(rand())/RAND_MAX*max;
int random_number = lower_bound+float(rand())/RAND_MAX*(upper_bound-lower_bound);
int random_number = float(rand())/RAND_MAX*max;
int random_number = lower_bound+float(rand())/RAND_MAX*(upper_bound-lower_bound);
#include <stdlib.h>#include <iostream.h>#include <time.h>void main(){ srand( (unsigned)time( NULL ) ); // generate your random seed cout << "Random number between 0 and 9: " << rand()%10 << endl; cout << "Random number between 0 and 19: " << rand()%20 << endl; cout << "Random number between 0 and 99: " << rand()%100 << endl; cout << "Random number between 0 and 5000: " << rand()%5001 << endl;} EDIT: forget source brackets ;-)
[edited by - bangz on May 5, 2002 9:23:09 PM]
quote:Original post by IndirectX
Never use modulus with rand. Use division instead, or you''ll screw up even distribution:
How would this affect the distribution?
If I wanted to get a random number in plain ansi c,
would I also have to create a ´seed´ first or use the time function? if do, how would I go about doing this?
thanx in advance
PEACE
would I also have to create a ´seed´ first or use the time function? if do, how would I go about doing this?
thanx in advance
PEACE
Carrot : if RAND_MAX == 10 and you call rand() % 3 the probability would be : 0=4 1=3 2=3. In the long run this makes for a big mistake and since that mistake is alway in the low number it imbalance things.
You should use this formula to have balanced probability :
Result = int(rand() / (RAND_MAX + 1.0f) * Delta)
You should use this formula to have balanced probability :
Result = int(rand() / (RAND_MAX + 1.0f) * Delta)
If RAND_MAX was 10, random numbers would suck.
However on my machine it''s 32767, so what''s the problem?
However on my machine it''s 32767, so what''s the problem?
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