c++ I am get always same number Radnom between 0 and 1

Asked Sep 15 '20 at 07:15

Active Sep 15 '20 at 07:23

Viewed 48 times

double Matrix::getRandomNumber()
{
    double r;

    srand(time(NULL));
    r = (double)rand()/RAND_MAX;

    return r;
}

I am always get same number.

and I tried this way:

double Matrix::getRandomNumber()
{
    std::random_device rd;
    std::mt19937 gen(rd());
    std::uniform_real_distribution<> dist(0,1);

    return dist(gen);
}

I am still get same Number. I am using code blocks. and c++14.

when I did this:

void Matrix::printToConsole()
{
    for(int y = 0; y<this->Cols; y++)
    {
        for(int x = 0; x<this->Rows; x++)
        {
            std::cout<<this->getRandomNumber()<<" ";
        }
        std::cout<<std::endl;
    }
}

it is my result on console:

0.518082 0.518082 0.518082 0.518082 0.518082
0.518082 0.518082 0.518082 0.518082 0.518082
0.518082 0.518082 0.518082 0.518082 0.518082
0.518082 0.518082 0.518082 0.518082 0.518082
0.518082 0.518082 0.518082 0.518082 0.518082

edited Sep 15 '20 at 07:23

asked Sep 15 '20 at 07:15

Muhammed Yaşar

5

Call `srand(time(NULL));` only once in your program at startup. – Jabberwocky Sep 15 '20 at 07:16
4

Each time you call `Matrix::getRandomNumber()`, you're creating a new instance of `std::random_device`. Make it static (`static std::random_device rd;`) or global, or otherwise persistant, e.g. by making it a static member of `Matrix`.. – Jabberwocky Sep 15 '20 at 07:21
I make it static. And that worked. Thanks a lot. – Muhammed Yaşar Sep 15 '20 at 07:25
2

[srand() — why call it only once?](https://stackoverflow.com/q/7343833/995714) – phuclv Sep 15 '20 at 07:26
But I get some numbers that is not between 0 and 1. I get this nums: 0.297901 0.563295 1.95833e-306 0.35442 0.318691 3.95576e-270 – Muhammed Yaşar Sep 15 '20 at 07:29
Perhaps you want to look up floating point arithmetic. – stephanmg Sep 15 '20 at 07:31
4

all those numbers are between 0 and 1. `1.95833e-306` is 0.000......00019583 – 463035818_is_not_an_ai Sep 15 '20 at 07:36

c++ I am get always same number Radnom between 0 and 1

0 Answers0