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.
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1http://stackoverflow.com/questions/2509679/how-to-generate-a-random-number-from-within-a-range – Mike Feb 02 '15 at 21:09
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@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
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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
2 Answers
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#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;
}
R Sahu
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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.
Roman Ambinder
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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
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@RomanAmbinder no, you modulo the random number with `(upper - lower + 1)` then add `lower`. – Weather Vane Feb 02 '15 at 21:26
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@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
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@chux that's true, but I commented on this answer not on the question. – Weather Vane Feb 02 '15 at 22:15