C: First value from rand() is zero (or other problem?)

John Kauffman

I've written below as an experiment. I always get zero as first output from rand(). Or maybe problem is elsewhere. Any suggestions? Thanks.

#include "simpletools.h"
int main(void){
int randomCurrent;
print("Count\tValues\tModuli range 0-5\n");
for(int count=1;count<=100;count++)
{
randomCurrent = rand();
print("%d.\t%d\t%d\n",count,randomCurrent,randomCurrent%6);
}


Terminal output always shows 0 for first entry:

---

Count Values Moduli range 0-5
1. 0 0
2. 21468 0
3. 9988 4
4. 22117 1
5. 3498 0

ersmith

The "random" sequence you get from rand() is always the same, and as it happens the default sequence does start with a 0. You can request a different sequence by calling srand(x) with some integer x before the first call to rand(). For example, if you call srand(99) then the first rand() result will return 28592.

If you have a real time clock or similar input that will vary each time the program runs, you can use a value from this as the input to srand() to ensure that rand() produces a different sequence each time.

kuroneko

srand(CNT) should do the trick.

John Kauffman

Perfect, thanks. I was suspicious of the seed.
I don't have RTC. Do you know of a way to get a seed from Prop ticks?
Much thanks.

John Kauffman

Perfect, much thanks.

Heater.

The Propeller can generate real random numbers by itself without any messing with keyboard click times and so on. See the Real Random object in OBEX:
http://obex.parallax.com/object/498
Should be relatively straightforward to implement that in C.

Depends on how random you want.