How to generate random number within x-y range, if x and y values varies [language C]

Question

How to generate random number within x-y range in C where

X : [t , t+m] and Y : [r , r+m ].

That is , if x varies from t to t+n and y varies from r to r+n.

http://stackoverflow.com/questions/2509679/how-to-generate-a-random-number-from-within-a-range — Mike, Feb 02 '15 at 21:09
@Mike Disagree that the post is a good duplicate as that one is about integers and this is FP - subtle difference, even though the over-all math is the same. Likely a dupe exist elsewhere though. — chux - Reinstate Monica, Feb 02 '15 at 22:03
This is not a duplicate question. It seems to be similar but it is different. Don't just go on title please read the question carefully before adding wrong links — Rishabh Agarwal, Mar 16 '17 at 19:41

score 1 · Accepted Answer · answered Feb 02 '15 at 21:16

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main()
{
   double x = 1.0;
   double y = 2.0;
   srand(time(NULL));

   // Guarenateed keep x1 between x and y.
   double x1 = x + rand()*(y-x)/RAND_MAX;

   printf("x1: %lf\n", x1);

   return 0;
}

score 0 · Answer 2 · answered Feb 02 '15 at 21:15

0

Basically you seed the generator with operation system ticks count, modulo your generated number with the upper range and add the lower range to the result.

answered Feb 02 '15 at 21:15

Roman Ambinder

369
3
7

That is not correct. For a range *x...y*, it will generate numbers between *x* and *x+y*. – Jongware Feb 02 '15 at 21:25
@RomanAmbinder no, you modulo the random number with `(upper - lower + 1)` then add `lower`. – Weather Vane Feb 02 '15 at 21:26
@Weather Vane the +1 suggested in `(upper - lower + 1)` does not quite apply to this OP's need as this code works with a FP range. In any case, modulo on OP's range 0.0 to 0.33333 is problematic. – chux - Reinstate Monica Feb 02 '15 at 22:11
@chux that's true, but I commented on this answer not on the question. – Weather Vane Feb 02 '15 at 22:15

How to generate random number within x-y range, if x and y values varies [language C]

2 Answers2