Question

Sorry for asking such a vague question, i’m new to using C# / ASP.NET. When creating randomly generated questions, and storing the question objects within a list through the use of a for loop the same / duplicate question is showing up when I output the questions. I’ve inspected the list of questions with the debugger, and it shows 10 of the same object.

Server-side C# Used to populate the list of questions:

private void Populate()
{
    __NumberOfQuestions = 10;
    __Questions = new List<Question>(__NumberOfQuestions);

    for (int i = 0; i < __NumberOfQuestions; i++)
    {
        __Questions.Add(new Question());
    }

    QuestionList.DataSource = __Questions;
    QuestionList.DataBind();
}

Question class is avaialable here:
http://pastebin.com/mEArQFHh

ASP Code used to add the questions to the page:

            <asp:Repeater ID="QuestionList" runat="server">
                <ItemTemplate>
                    <tr>
                        <td><%#DataBinder.Eval(Container.DataItem,"__LeftOperand")%></td>
                        <td><%#DataBinder.Eval(Container.DataItem,"__Operator")%></td>
                        <td><%#DataBinder.Eval(Container.DataItem,"__RightOperand")%></td>
                        <td><%#DataBinder.Eval(Container.DataItem,"__Answer")%></td>
                    </tr>
                </ItemTemplate>
            </asp:Repeater>

Output:

9
SUBTRACT
6
3
9
SUBTRACT
6
3
9
SUBTRACT
6
3
9
SUBTRACT
6
3
9
SUBTRACT
6
3
9
SUBTRACT
6
3
9
SUBTRACT
6
3
9
SUBTRACT
6
3
9
SUBTRACT
6
3
9
SUBTRACT
6
3

Answer 1

What you’re doing wrong:

1. You create a new Random object for each Question.
2. Since you don’t provide an argument to the Random constructor, the default,
   time-based, seed is used. This uses Environment.TickCount (though I don’t think this is documented specifically), so it has millisecond granularity.
3. Since you construct all of your questions in the same millisecond,
   they’ll use the same seed.
4. This means that they’ll get the same sequence of random numbers.
5. This means that you get 10 different questions, but all with the
   same values.

The simplest way to fix this is to make your Random object static, which means it’s shared by all of the Question objects — or belongs to the Question class, rather than to question instances. This means it’ll only be constructed once, and you’ll get a sensible sequence of random numbers.