Create a random even number between range

Question

OK I need to create an even random number between 54 and 212 inclusive. The only catch is that it has to be done in a single statement. I have a class to generate random number within a range, but like I said, I want to do it in a single statement. I came up with this, but it's not working correctly. Any ideas?

int main()
{
 srand( time(NULL));
 int i;
 i = (rand() % 106) * 2;
 cout << i;
 return 0;
}

• Darin Dimitrov: Is this some kind of a homework?
• kerkeslager: Why do you want to do this in a single statement? Is this homework?

Answer 1

Generate any number in the interval [27, 106] and multiply it by 2. Your problem is that you have no lower bound.

int i = 2 * (27 + rand() % (106 - 27 + 1)) 

In general, to generate a random number in [a, b] use:

int i = a + rand() % (b - a + 1)

To see why this works, try simple examples such as [2, 4], [3, 7] etc.

• user2493476: Can you please explain the logic?
• IVlad: @Goutam - rand() generates a random number >= 0. Taking it modulo b - a + 1 will put it in [0, b - a]. Adding a will put it in [a, b].