Random odd numbers between range with the exception of a single number in C

Question

Here is my code:

alpha = ((rand() % 12) + 1) * 2 + 1;

I want to generate random odd numbers between 0-25. But except integer 13. How can I fix this? Thank you.

Answer 1

Generates number from 0 to 23. If it's a 13, then store 25 in your variable :

alpha = ((rand() % 11) + 1) * 2 + 1;
if (alpha == 13) alpha = 25;

Answer 2

Make a simple loop to retry the operation if alpha gets 13 :

  int alpha = 13;
  while (alpha == 13)
    alpha = ((rand() % 12) + 1) * 2 + 1;

Answer 3

int universe[] = {1, 3, 5, 7, /* ... omit 13 ... */ 25};
int index = randto(sizeof universe / sizeof *universe);
alpha = universe[index];

Where randto(n) returns a random number from 0 up to and excluding n.