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Posted 26 Jan 2011

# How to generate many random various numbers?

, 28 Jan 2011
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How to generate many random various numbers?
1. We need an array of random various numbers between x[0] and x[n] like shuffling the cards.

For example: 8, 10, 5, 4, 7, 6, 3, 1, 9, 2 (between 1 and 10)

The following code is a method (with an overload) and generates an array of random various integer numbers:

```//C#
public static int[] RandomNumbers(int min, int max)
{
return RandomNumbers(min, max, 2);
}
public static int[] RandomNumbers(int min, int max, int derangement)
{
if (min > max)
{
throw new Exception("The first parameter must be less (or equal) than the second.");
}
Random random = new Random();
int count = max - min; ;
int[] tempList = new int[count + 1];
int counter = 0;
for (int i = min; i <= max; i++)
{
tempList[counter] = i;
counter++;
}

for (int i = 0; i < derangement; i++)
for (int j = 0; j < count; j++)
{
int k = random.Next(0, count + 1);
int l = random.Next(0, count + 1);
if (k != l)
{
//Swap TempList[k] with TempList[l]
tempList[k] += tempList[l];
tempList[l] = tempList[k] - tempList[l];
tempList[k] = tempList[k] - tempList[l];
}
}
return tempList;
}```

Note: `derangement` is an integer variable to define the chance of the numbers derangement, but there is an inversely relationship between the performance and the value of the variable. The overload default is 2.

Now, It's ready to use the method:

```//C#
int[] m = RandomNumbers(1, 56, 5);
foreach (int i in m)
{
Console.Write("{0}, ",i);
}

2. We need to generate a random number which has not been generated since runtime.

There has been a generated random number previously, but need to have a different one:

```//C#
public static int RandomNumber(ref List<int> numbers, Random random)
{
int count = numbers.Count;
int randomIndex = random.Next(0, count);
int returnedNumber = numbers[randomIndex];
numbers.RemoveAt(randomIndex);
return returnedNumber;
}```

It's requisite for using the method, to have a random variable and a list of numbers, for example:

```//C#
Random random = new Random();
List<int> numbers = new List<int>();
for (int i = 0; i <= 1000; i++)
{
}

//Ok, For each using the method, there is a new and defferent random number:

Console.WriteLine(RandomNumber(ref numbers, random));
Console.WriteLine(RandomNumber(ref numbers, random));
Console.WriteLine(RandomNumber(ref numbers, random));
Console.WriteLine(RandomNumber(ref numbers, random));
Console.WriteLine(RandomNumber(ref numbers, random));

The second approach has a better performance.

Good Luck!

## About the Author

 Software Developer (Senior) Iran (Islamic Republic of)
Microsoft Certified Technology Specialist (MCTS)

"شاهین خورشیدنیا"

Nobody is perfect and neither am I, but I am trying to be more professional. In my humble opinion, you have to develop your skills, as long as you are responsible for developing even a tiny part of a sustainable software. That makes this job so special to me.

## Comments and Discussions

 View All Threads First Prev Next
 Reason for my vote of 1 A better way of doing this has been ... Henry.Ayoola31-Aug-11 21:46 Henry.Ayoola 31-Aug-11 21:46
 Re: Thank you. And would you explain why that way is better? Shahin Khorshidnia1-Sep-11 10:34 Shahin Khorshidnia 1-Sep-11 10:34
 Last Visit: 31-Dec-99 18:00     Last Update: 26-Jul-17 7:13 Refresh 1

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