randomness algorithm

Question

I need some help regarding algorithm for randomness. So Problem is.

There are 50 events going to happen in 8 hours duration. Events can happen at random times. Now it means in each second there is a chance of event happening is 50/(8*60*60)= .001736. How can I do this with random generation algorithm?

I can get random number

int r = rand();
double chance = r/RAND_MAX;
if(chance < 0.001736)
    then event happens
else
    no event

But most of times rand() returns 0 and 0<0.001736 and I am getting more events than required.

Any suggestions?

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sorry I forget to mention I calculated chance as double chance = (static_cast )(r) / (static_cast)(RAND_MAX);

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It removed double from static_cast

double chance = (double)r/(double)(RAND_MAX);

Answer 1

Both r and RAND_MAX are integers, so the expression

double chance = r / RAND_MAX;

is computed with integer arithmetic. Try:

double chance = 1.0 * r / RAND_MAX;

which will cause the division to be a floating point division.

However, a better solution would be to use a random function that returns a floating point value in the first place. If you use an integer random number generator, you will get some bias errors in your probability calculations.