How can you make a random number generator that chooses between the number 2 or 3. (not 1,2,3)

Question

Hi I am working on a monty hall generator and in part of my code I need it to generate random number 2 or 3. It cannot be 1,2,3 but the computer needs to select between 2 or 3. Thanks!

I have tried randomCarDoor = ( rand() % 3 ) + 1; but does not work.

randomCarDoor = ( rand() % 3 ) + 1;

It gives me the number 1,2,3 but I just want 2 and 3

Answer 1

You can use the low order bit of the random value, but it is very risky as some pseudo-random number generators do not provide adequate dispersion on low order bits:

int two_or_three = 2 + rand() % 2;

A much better way is to use the magnitude of the random number which is specified as having a flat distribution:

int two_or_three = 2 + (rand() >= RAND_MAX / 2);

If you want numbers 1 and 3, here is a simple solution for any pair:

int random_value = (rand() < RAND_MAX / 2) ? 1 : 3;