I have a lottery application in C# which takes in the number of numbers to draw and also the maximum number to draw.I have coded up to creating an array holding the required random numbers but I need them to be unique and am having trouble doing it.I would be very grateful if someone could give me some advice on this,Thanks
Here is my code so far:
class Lottery
{
static int[] numberHolder; //array to be filled with numbers up to an
//amount entered by the user eg 42 Max
static int[] drawHolder; //array to hold the each random number
//drawn from the pool of numbers eg 7 numbers
public Lottery() //Lottery class Constructor
{
}
//method which takes in a number limit and amount of numbers to be drawn
public String drawNumbers(int numLimit, int numAmount)
{
Random RandomNumber = new Random();
for (int i = 0; i < numLimit ; i++) //loop to fill up numberHolder array
// with predefined limit of numbers
{
numberHolder[i] = i++;
}
for (int i = 0; i < numAmount; i++)
{
// code to pick unique random numbers no greater than numAmount
// and add them to the drawHolder[] array
drawHolder[i] = RandomNumber.Next(1, numLimit);
}
//return the drawHolder array to String
return null;
}
}
In my opinion, you should change your approach.
Instead of thinking "I'll generate random indexes to pick my numbers", where you have to be sure you don't get any duplicates, I would simply shuffle the array and take the X first you need. That way, you don't need to worry about indexes or duplicates.
So your second for loop would be changed to
drawHolder = numberHolder.OrderBy(x => new Guid()).Take(numAmount);
(Please note I've used new Guid() so you can remove your RandomNumber declaration line. As discussed before, a GUID is a unique value and not meant for to be used as a random gen. You could also use x => RandomNumber.Next(), but if you really need a strong and reliable shuffe, read about Fisher-Yates)
You can also replace your numberHolder array with a simple Enumerable.Range
So your whole code would become (And please note I've changed your method name to use C# conventions, method names should be in PascalCase)
public string DrawNumbers(int numLimit, int numAmount)
{
drawHolder = Enumerable.Range(0, numLimit).OrderBy(x => new Guid()).Take(numAmount);
return string.Join(", ", drawHolder);
}
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