Question

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Random number generator not working the way I had planned (C#)

I have this code in c# but I get a result the same number, what is it wrong?

like a21, a21, a21….

        String c = "";
        int randomNumber = 0;
        for (int i = 0; i < 20; i++)
        {
            randomNumber = RandomNumber(0, 617);
            c += "a " + randomNumber + ", ";                    
        }
        file.WriteLine(c);



I am using this function

public static int RandomNumber(int min, int max)
    {
        Random random = new Random();
        return random.Next(min, max);
    }

Answer 1

You should pass the Random as parameter to your function. Although your function has no added value then anymore.

var rnd = new Random();
for (int i = 0; i < 20; i++)
{
    randomNumber = RandomNumber(rnd ,0, 617);
    c += "a " + randomNumber + ", ";                    
}

public static int RandomNumber(Random rnd, int min, int max)
{
    return rnd.Next(min, max);
}

Every time you do new Random() it is initialized using the clock. This means that in a tight loop you get the same value lots of times. You should keep a single Random instance and keep using Next on the same instance.

https://stackoverflow.com/a/768001/284240

Edit: i read in your comment that you want to create 20 unique numbers in the given range, here is one way using HashSet<int>:

HashSet<int> uniqueNumber = new HashSet<int>();
var rnd = new Random();
while(uniqueNumber.Count<20){
    var nextNum = rnd.Next(0, 617);
    uniqueNumber.Add(nextNum);
}