How to randomly fill checkboxes in c# - Visual Studio

Question

So this is my first question on stack overflow. I'm working on a drum sequencer and want to implement a button to randomly fill the 80 checkboxes that indicate a drum sound being triggered. Currently what I have only filles one box of the 80 randomly, but I want each of them to have a random chance of being filled. The first part of my code simply clears the current selection. Here is my attempt in the following code:

private void button4_Click(object sender, EventArgs e)
{
    List<CheckBox> Checkboxlist = new List<CheckBox>();
    foreach (CheckBox control in this.Controls.OfType<CheckBox>())
    {
        Checkboxlist.Add(control);
        control.Checked = false;
    }

    for (int i = 0; i <= 200; i++)
    {
        var random = new Random();
        var r = random.Next(0, Checkboxlist.Count);
        var checkbox = Checkboxlist[r];
            checkbox.Checked = true;
    }
}

Thank you for looking!

move `var random = new Random();` out of the loop or you'll have random sequence *badly skewed* — Dmitry Bychenko, Oct 24 '16 at 20:05

nrofis · Accepted Answer · 2020-10-05T14:20:24.283

Don't create new Random() inside the loop. It is better to declare the random once, the best way is to create it as static member.

private static Random random = new Random(); // Class member

private void button4_Click(object sender, EventArgs e)
{
    List<CheckBox> Checkboxlist = new List<CheckBox>();
    foreach (CheckBox control in this.Controls.OfType<CheckBox>())
    {
        Checkboxlist.Add(control);
        control.Checked = false;
    }

    for (int i = 0; i <= 200; i++)
    {
        var r = random.Next(0, Checkboxlist.Count);
        var checkbox = Checkboxlist[r];
        checkbox.Checked = true;
    }
}

The reason for that is:

The random number generation starts from a seed value. If the same seed is used repeatedly, the same series of numbers is generated. One way to produce different sequences is to make the seed value time-dependent, thereby producing a different series with each new instance of Random. By default, the parameterless constructor of the Random class uses the system clock to generate its seed value,

Source

The rapid for-loop cause the Random to be created with the same seed, so the Next function returned the same first value of the series of numbers.

Better to put the checking in the first foreach loop: control.Checked = random.Next(0,99)>=50. //(eg. 50% to be checked) — lintabá, Jan 22 '18 at 03:22

score 1 · Answer 2 · answered Oct 24 '16 at 20:08

You should move the Random declaration out of the for loop:

var random = new Random();
for (int i = 0; i <= 200; i++)
{
    var r = random.Next(0, Checkboxlist.Count);
    var checkbox = Checkboxlist[r];
        checkbox.Checked = true;
}

score 0 · Answer 3 · answered Oct 24 '16 at 20:12

To go through and change to random values in all instances, this may work for you.

private void button4_Click(object sender, EventArgs e)
{
    List<CheckBox> Checkboxlist = new List<CheckBox>();
    foreach (CheckBox control in this.Controls.OfType<CheckBox>())
    {
        Checkboxlist.Add(control);
        control.Checked = false;
    }
    Random r = new Random();
    int g = 0;
    for ( int i = 0; i < Checkboxlist.Length; i++){
        g = r.Next(0,1);
        if(g ==1)
            Checkboxlist[i].Checked = true;
    }
}

How to randomly fill checkboxes in c# - Visual Studio

3 Answers3