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Alek Richter
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Enlightened
Asked: 2021-12-23T07:30:51+00:00

How to generate a random number in C++?

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I’m trying to make a game with dice, and I need to have random numbers in it (to simulate the sides of the die. I know how to make it between 1 and 6). Using

#include <cstdlib> 
#include <ctime> 
#include <iostream>

using namespace std;

int main() 
{ 
    srand((unsigned)time(0)); 
    int i;
    i = (rand()%6)+1; 
    cout << i << "\n"; 
}

doesn’t work very well, because when I run the program a few times, here’s the output I get:

6
1
1
1
1
1
2
2
2
2
5
2

So I want a command that will generate a different random number each time, not the same one 5 times in a row. Is there a command that will do this?

1 Answer

  2. Enlightened

    Using modulo may introduce bias into the random numbers, depending on the random number generator. See this question for more info. Of course, it’s perfectly possible to get repeating numbers in a random sequence.

    Try some C++11 features for better distribution:

    #include <random>
#include <iostream>

int main()
{
    std::random_device dev;
    std::mt19937 rng(dev());
    std::uniform_int_distribution<std::mt19937::result_type> dist6(1,6); // distribution in range [1, 6]

    std::cout << dist6(rng) << std::endl;
}

    See this question/answer for more info on C++11 random numbers. The above isn’t the only way to do this, but is one way.

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