C++乱数生成の2つの方法--指定範囲内の乱数を生成する

1つ目は伝統的な方法です.

#include 

using namespace std;

int main() {
    srand(NULL);
    for (int i = 0; i < 100; i++) {
        cout << rand() << ' ';
    }
    return 0;
}

この方法は伝統的で,欠点はランダム性が不十分で,生成したランダム数の範囲を自分で選択できないことである.短時間でsrand(NULL)を複数回呼び出すと、生成される乱数は同じです.c-srand(time(NULL))doesn’t change seed value quick enough-Stack Overflow
新しいC++11のやり方は以下の通りです.

#include 
#include 

int main() {
    std::random_device rd;     //Get a random seed from the OS entropy device, or whatever
    std::mt19937_64 eng(rd()); //Use the 64-bit Mersenne Twister 19937 generator
                                //and seed it with entropy.

    //Define the distribution, by default it goes from 0 to MAX(unsigned long long)
    //or what have you.
    std::uniform_int_distribution<unsigned long long> distr;

    //Generate random numbers
    for (int n = 0; n < 40; n++){
        std::cout << distr(eng) << ' ';
    }
    std::cout << std::endl;
}

たとえば、1～6の乱数を生成したい場合は、次のようにします.

#include 
#include 

int main() {
    std::random_device rd;     //Get a random seed from the OS entropy device, or whatever
    std::mt19937_64 eng(rd()); //Use the 64-bit Mersenne Twister 19937 generator
    //and seed it with entropy.

    //Define the distribution, by default it goes from 0 to MAX(unsigned long long)
    //or what have you.
    std::uniform_int_distribution<unsigned long long> distr(1, 6);// distribution in range [1, 6]

    //Generate random numbers
    for (int n = 0; n < 40; n++) {
        std::cout << distr(eng) << ' ';
    }
    std::cout << std::endl;
}

参照:c++-Generating random integer from a range-Stack Overflow