Error while using Random

Question

I set a random number to fill a fictitious table and did so:

    foreach (var usuario in LstUsuarios)
    {
        htmlUsuarios.AppendLine("<tr>");
        htmlUsuarios.AppendLine("<td>" + usuario.Nome + "</td>");
        htmlUsuarios.AppendLine("<td><strong>" + usuario.NomePerfil + "</strong></td>");
        htmlUsuarios.AppendLine("<td>" + usuario.UnidadeGerencial.Txt_Sigla_UG + "</td>");

        for (var i = 1; i <= num_periodos; i++)
        {
            rnd = new Random();
            random = rnd.Next(1, 99);
            htmlUsuarios.AppendLine("<td> " + random + "</td>");
        }
        htmlUsuarios.AppendLine("<td>100</td>");
        htmlUsuarios.AppendLine("</tr>");
    }

But the application is always showing the same number.

The curious thing is that when I debug in the visual studio it actually generates different numbers.

What is outside the red line is the part that I debugged in VS, I was checking with the breakpoints and the numbers were changing. But when I pressed keep on the VS it would generate the same number as the ones inside the red line.

I don’t understand why. Any idea?

Answer 1

Put the instância of Random() outside the for in your case:

rnd = new Random();
foreach (var usuario in LstUsuarios)
{
    htmlUsuarios.AppendLine("<tr>");
    htmlUsuarios.AppendLine("<td>" + usuario.Nome + "</td>");
    htmlUsuarios.AppendLine("<td><strong>" + usuario.NomePerfil + "</strong></td>");
    htmlUsuarios.AppendLine("<td>" + usuario.UnidadeGerencial.Txt_Sigla_UG + "</td>");

    for (var i = 1; i <= num_periodos; i++)
    {            
        random = rnd.Next(1, 99);
        htmlUsuarios.AppendLine("<td> " + random + "</td>");
    }
    htmlUsuarios.AppendLine("<td>100</td>");
    htmlUsuarios.AppendLine("</tr>");
}

Because?

How is being created the Random within the is each generated item is a new instance, and with that the initial Seed is the same, fact calculated by Enviroment.Tickcount.

About the debug:

Precisely because of the Enviroment.Tickcount will have another value in debug, and in each F11 for example, will change the millisecond calculation.