How do you get a random number between two numbers?

Question

Hello,
I would like to get a random number between two numbers a and b. I think to get that you have to use : a + (rand() % b) is it right?
But the code doesn't work that well in my case...
cout << 8 + (rand() % 16);
often prints values over 16...
Can you help me, tell me where I'm wrong?
Thanks!!
Here's the full code if you need it:
https://code.sololearn.com/cyKaVVB38pkM/?ref=app

Answer 1

It will generate out of range for sure. I will explain you why. For your example you want random number between 8-16(Including boundaries)
rand()%16 will generate any random number from 0-15 and you areadding 8 to it. So if rand()%16 generates number which is greater than 8 that would finally generate number grater than 16.(10+8).

Solution :
// including bounries
randomNumber = lowerLimit + (rand() %(higherLimit - lowerLimit+1));

//excluding boundries
randomNumber = (lowerLimit+1) + (rand()%(higherLimit-lowerLimit-1));

Note, if you use this formula make sure boundies are valid.means, higherLimit is always higher than lowerLimit.

Hope that helps. Thanks.

Answer 2

use this logic

rand()%(max-min+1)+min

so in your code:

int Number = 8 + (rand() % (16-8+1));

Answer 3

All right it works fine, thank you very much!

Answer 4

Thank you, now I understand why that occured... I'll remember that, thanks for your help!