arc4random except some numbers

Question

How can you disallow some nubers from being chosen with the arc4random function?

Current code:

int random = (arc4random() % 92);

(numbers from 0 to 92)

I want it do disallow the following numbers: 31, 70, 91, 92

Thank you (:

Answer 1

First, you'll need to change

% 92

to

% 93

to get numbers from 0..92

I'd do something like this

int random;

do {
    random = arc4random() % 93;
}
while ( random == 31 || random == 70 || random == 91 || random == 92 );

Answer 2

Simple, keep asking for numbers:

get a new random number
while the new number is one of the disallowed ones:
    get a new random number
return the random number

Pseudo code, but you should get the idea.

Answer 3

If you are going to disallow numbers 91 and 92, why bother including them in your mod?

Expanding on the previous answer:

int random;
do {
    random = arc4random() % 91;
}
while ( random == 31 || random == 70 );