Random

The Random type returns a stream of numbers. It is best used as a field—this improves results when called from multiple methods.

It is important to understand the 2 arguments to random methods in VB.NET. The second value is exclusive—so it is never included in the results.

Next method

We create a Random class instance with its constructor. And with Next, we pass up to 2 arguments. Default values are used if we do not specify them as arguments.

Module Module1

    Sub Main()
        Dim r As Random = New Random
        ' Get random numbers between 5 and 10.
        ' ... The values 5 through 9 are possible.
        Console.WriteLine(r.Next(5, 10))
        Console.WriteLine(r.Next(5, 10))
        Console.WriteLine(r.Next(5, 10))
    End Sub

End Module
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Field

For modules or classes, it is best to store a Random number generator as a field. The Random instance will not repeat itself as much.

Module Module1

    Sub Main()
        ' Write three random numbers.
        F()
        F()
        F()
    End Sub

    ''' <summary>
    ''' Write the next random number generated.
    ''' </summary>
    Private Sub F()
        ' Call Next method on the random object instance.
        Console.WriteLine(_r.Next)
    End Sub

    ''' <summary>
    ''' Store a random number generator.
    ''' </summary>
    Private _r As Random = New Random

End Module
1284029964
984949494
1322530626

Random bytes

Sometimes we need to generate many random numbers at once. If we need bytes, we can generate random bytes with NextBytes.

Module Module1

    Sub Main()
        Dim randomGenerator = New Random()

        ' Array of 10 random bytes.
        Dim buffer(9) As Byte

        ' Generate 10 random bytes.
        randomGenerator.NextBytes(buffer)

        For Each value In buffer
            Console.Write("[{0}]", value)
        Next
    End Sub

End Module
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It is important to use the Random type as a field in some situations, to reduce the possibility of repetition. Having fewer Random number generators is also more efficient.