how do I "roll" for a 25% chance to get YES or NO?

Question

I'd like to randomly generate a YES or NO based on a percentage

So I want to "roll" and have a 25% chance to hit YES, a 75% chance to hit NO

Was hoping someone could point me in the right direction on the best way to do this, maybe some article or something?

Answer 1

All of the other answers seem to focus on the percentage of YES being 25%, which is a probability of 1/4. But what if the percentage is an arbitrary integer between 0 and 100?

BOOL randomBoolWithYesPercentage(int percentage) {
    return arc4random_uniform(100) < percentage;
}

Call it with the percentage, like randomBoolWithYesPercentage(25).

And what if the percentage can be fractional, like 37.6%? Then we need to get more sophisticated. This should suffice:

BOOL randomBoolWithYesPercentage(double percentage) {
    double r = 100 * (double)arc4random() / ((double)UINT32_MAX + 1);
    return r < percentage;
}

Answer 2

Use a random function with an equal distribution and make it as likely as you want to equal one of the possible values

BOOL RollWithDenominator(NSInteger denominator)
{
  return 0 == arc4random_uniform(denominator);
}

For a 1/4 chance call RollWithDenominator(4);