picking rand() number from 1-6

Question

I have a simple problem here but no clue how to fix this! I am trying to create a number generator but I only want it to pick a random number from 1-6. No zeros! This question was marked a dup but it shouldn't be because this is C++ NOT C:

srand(static_cast<unsigned int>(time(0)));
int dice = rand()%6;

@GrijeshChauhan - `rand()/RAND_MAX` will be 0 almost all the time; both expressions have type `int`, and the value returned by `rand()` is never greater than the value of `RAND_MAX`. Use `rand()/double(RAND_MAX)`, or your favorite variant. — Pete Becker, Aug 08 '13 at 11:28
It is kind of silly to close a C++ question as a dup of a C question since many C++ solutions are not valid C solution, at least find a dup w/ the right tags. — Shafik Yaghmour, Aug 09 '13 at 00:18

score 13 · Accepted Answer · answered Aug 08 '13 at 03:52

13

rand() % 6 gives a number in the range 0..5. Add one to get the range 1..6.

answered Aug 08 '13 at 03:52

Mike Seymour

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score 9 · Answer 2 · edited May 23 '17 at 11:54

9

If C++11 is an option you also have std::uniform_int_distribution which is somewhat simpler and less error prone(see rand() Considered Harmful presentation and slides):

#include <iostream>
#include <random>

int main()
{
    std::random_device rd;

    std::mt19937 e2(rd());

    std::uniform_int_distribution<> dist(1, 6);

    for( int i = 0 ; i < 10; ++i )
    {
       std::cout << dist(e2) << std::endl ;
    }

    return 0 ;
}

This previous thread Why do people say there is modulo bias when using a random number generator? explains clearly the modulo bias that chris pointed out in his comment.

edited May 23 '17 at 11:54

Community

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answered Aug 08 '13 at 04:01

Shafik Yaghmour

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And much better than the `rand()` generator combined with modulus bias. – chris Aug 08 '13 at 04:01
@chris Added a link explaining modulo bias – Shafik Yaghmour Aug 08 '13 at 13:24

score 4 · Answer 3 · answered Aug 08 '13 at 03:54

4

Almost got it:

int dice = rand()%6 + 1;

answered Aug 08 '13 at 03:54

John

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picking rand() number from 1-6

3 Answers3