Thread: rand() function is not really random

I made a dice program using

Code:

dice=rand()%6 + 1;

It gives random values from 1 to 6 but every time I run the program, it just gives me the same set of random values.I tried using

Code:

random=(rand()*time(NULL))%6 + 1;if(random>0) //since random sometimes become negative{     dice=random; }

But this one always shows 1 and sometimes the other numbers. It's like 90% chance of getting 1 and I do not know why.

I think you forgot to seed srand() with a new value each time(at the beginning).
srand(time(NULL)) is often used, as everytime you run, the time is going to differ slightly.

[FONT=Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace]seed it...

use srand function..

Code:

srand(time(NULL));

[/FONT]

You could do any of these options as well:

- Use a more cryptographically secure random generator. Arc4random() is not standard, but it's available on pretty much every Linux/Mac/*nix build I've seen. Also, a whole array of functions like this can be found here > jrand48(3) - Linux man page

- Seed your random, using srand(time(NULL));

- Write a "hack" quick random function:

Code:

#include <sys/time.h>


uint64_t fake_rand(int clamp)
{
	uint64_t val;


	asm ("rdtsc" : "=A" (val) : : );


	return (val % clamp);
}