Using a modulus operator to get a random variable in a certain range

Question

Sorry, I know there are similar questions already posted but this book is confusing me nonetheless.

In "C Programming: Absolute Beginner's Guide", there is a line:

dice1 = (rand() % 5) + 1;

to generate a random number between 1 to 6 for a dice game.

Isn't this an error? From my understanding, you cannot get a remainder of 5 using % 5 so that line would only generate numbers from 1 to 5. I'm an absolute beginner so I can't tell if I'm making an error or the book is. Could someone confirm?

You are correct on this. The book, if it claimed the number would be from 1 to 6, is wrong. — StoryTeller - Unslander Monica, May 13 '17 at 21:35
Is it fair to close this as 'trivial typo' when the 'trivial typo' is the property of a book's author, not the OP of the question? — Jonathan Leffler, May 13 '17 at 21:36
Yes, please do so. I just wanted a confirmation because I wasn't sure if it was a typo or my misunderstanding of modulus. — 5areductase, May 13 '17 at 21:38
Yes that is an error. To generate number between 1 - 6 we need to write - `rand()%6 + 1` — GAURANG VYAS, May 13 '17 at 21:40
Voted to close as requested, but hope you don't lose the rep. — Weather Vane, May 13 '17 at 21:41

score 0 · Accepted Answer · answered May 13 '17 at 21:44

Yes, 5 % 5 == 0, so you could only get numbers 1 to 5 from the full expression. The other issue with that method is that rand() probably returns numbers from 0 to 2ⁿ-1, so the total number of different values can only be divided equally to some other power of two. So the modulus doesn't give an even distribution of the resulting numbers, even assuming rand() itself gives evenly distributed values along its output range.

Using a modulus operator to get a random variable in a certain range

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