CODEWITHSUNDEEP
vb.net
MrTickles
MrTickles

Reputation: 61

Calculating digits of Pi

Hi I'm trying to calculate digits of pi using the Nilakantha series, however when i reaches 645 I just get an overflow error, could anyone help me understand what I'm doing wrong and how to fix it?

The Nilakantha series is: π = 3 + 4/(2*3*4) - 4/(4*5*6) + 4/(6*7*8) - 4/(8*9*10) + 4/(10*11*12) - 4/(12*13*14)...

Here's my code:

    Dim pi As Decimal


    pi = 3D
    For i = 1 To 100000
        If i Mod 2 = 1 Then
            pi += 4 / ((2 * i) * ((2 * i) + 1) * ((2 * i) + 2))
        ElseIf i Mod 2 = 0 Then
            pi -= 4 / ((2 * i) * ((2 * i) + 1) * ((2 * i) + 2))
        End If
    Next

    Console.WriteLine(pi.ToString)
    Console.Read()

Thanks so much,

Upvotes: 0

Views: 409

Answers (1)

Andrew Morton
Andrew Morton

Reputation: 25013

The denominator is being calculated as an Integer and so falls outside the range for an Integer.

You can coerce it into using Decimal values simply by introducing a Decimal into the calculation:

Dim pi As Decimal = 3D

For i = 1 To 100000
    If i Mod 2 = 1 Then
        pi += 4 / ((2D * i) * ((2 * i) + 1) * ((2 * i) + 2))
    Else
        pi -= 4 / ((2D * i) * ((2 * i) + 1) * ((2 * i) + 2))
    End If
Next

Console.WriteLine(pi.ToString)

Console.ReadLine()

Outputs:

3.1415926535897929884701432528

Close, but no cigar.

Upvotes: 1

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