random number generation

[Bo Sun]

hi,

I would like to code the following problem:

there are 4 events, and their happening probability is:

e1 with probability 0.5
e2 with probability 0.2
e3 with probability 0.2
e4 with probability 0.1

I want to use some random function generation function. when its return
value is [0. 0.5), I select e1, when it is [0.5, 0.75), I select e2..

My question is: which function should I use to generate [0, 0.5).. based
on the probability? How should I code this?

Many thanks,

Bo

 

[Nudge]

I would like to code the following problem:

there are 4 events, and their happening probability is:

e1 with probability 0.5
e2 with probability 0.2
e3 with probability 0.2
e4 with probability 0.1

I want to use some random function generation function. when its return
value is [0. 0.5), I select e1, when it is [0.5, 0.75), I select e2..

My question is: which function should I use to generate [0, 0.5).. based
on the probability? How should I code this?

#include <stdlib.h>

double p = (double)rand() / (double)RAND_MAX;

if (p < 0.5) return e1;
if (p < 0.7) return e2;
if (p < 0.9) return e3;
else return e4;