Random Numbers

are u working in the correct namespace?

make sure to include the correct header.

#include &ltstdlib.h>

NOTE: a hint to VC users. if you type the name of the function and search the help. you'll notice the help lets you know which header to include and which library to link when using the specified function. you can also goto MSDN and do the same thing.

To the vast majority of mankind, nothing is more agreeable than to escape the need for mental exertion... To most people, nothing is more troublesome than the effort of thinking.

[edited by - jenova on January 24, 2003 11:29:18 AM]

I once made a function to get a random integer within a certain range. Thought it might be helpfull.

int random(int max, int min)
{
   float randomnr = rand();
   randomnr = randomnr / RAND_MAX;
   return int( ((max - min) * randomnr) + min );
}

void main()
{
   // randomize
   srand((unsigned)time(NULL));
   // generate a random number between 1 and 10
   int i = random(1,10);
}
 

Thanks tons guys

quote:

---

Original post by Vich
I once made a function to get a random integer within a certain range. Thought it might be helpfull.

int random(int max, int min)
{
   float randomnr = rand();
   randomnr = randomnr / RAND_MAX;
   return int( ((max - min) * randomnr) + min );
}

void main()
{
   // randomize
   srand((unsigned)time(NULL));
   // generate a random number between 1 and 10
   int i = random(1,10);
}
  

---

I tried this in VC++ and I keep getting the same random numbers. Any other simplish way to get random numbers?

#include <iostream>
#include <cstdlib>
using namespace std;


int RandInt(int min, int max)
{
    if(min == max)
        return max;

    return rand()%(max - min) + min;
}
 
int main()
{
	for(int i = 0; i < 10; i++)
		cout << "Random number between 1 and 10: " << RandInt(1, 10) << endl;
	return 0;
}
  

output:

Random number between 1 and 10: 6
Random number between 1 and 10: 9
Random number between 1 and 10: 8
Random number between 1 and 10: 5
Random number between 1 and 10: 9
Random number between 1 and 10: 2
Random number between 1 and 10: 4
Random number between 1 and 10: 1
Random number between 1 and 10: 8
Random number between 1 and 10: 3
Press any key to continue
 

[edit- damn code tags...]

-eldee
;another space monkey;
[ Forced Evolution Studios ]

Do NOT let Dr. Mario touch your genitals. He is not a real doctor!


[edited by - eldee on January 28, 2003 12:52:32 AM]

OK, if I use that I get a random number everytime. But I call it three times in a row and get the same number.

You have to generate a random seed to get different numbers each time you run the program if you''re using rand().

If you call : srand(timeGetTime()); at the start of the program that should give you different numbers each time.

You''ll have to #include <mmsystem.h> and link winmm.lib to use timeGetTime().

Insane, I was seeding the srand() in the function that generated the random number and got the same one every time. Seeded it in WinMain() and it works great. What gives with that one?

You could do something like this:

I got my random numbers just by moving when I seed it at. My question is if I was seeding the generator with the system time everytime I called the function why was it coming up with the same number?

Because you were seeding it to the same thing each time. The time function returns seconds (I think) and you were calling rand several times a second. Each time you called it (since it was in the same second) it ended up with the same seed.

Also, if you want a really good pseudo-random number generator (depending on the compiler, the rand function might only return 16 bits, and it might not have a large period), you can use the Mersenne Twister(
http://www.math.keio.ac.jp/matumoto/emt.html) which is supposedly just as fast as rand and its one of the best pseudo-random number generators.

[edited by - Extrarius on January 29, 2003 3:08:36 PM]

I guess if I had stopped to think about it for a second I could have figured it out that it was using the same seed. Thanks for the enlightenment though.