# Fibonacci numbers (Visual Basic .NET)

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The Fibonacci numbers are the integer sequence 0, 1, 1, 2, 3, 5, 8, 13, 21, ..., in which each item is formed by adding the previous two. The sequence can be defined recursively by

$F(n) = \begin{cases} 0 & n = 0 \\ 1 & n = 1 \\ F(n-1)+F(n-2) & n > 1 \\ \end{cases} .$

Fibonacci number programs that implement this definition directly are often used as introductory examples of recursion. However, many other algorithms for calculating (or making use of) Fibonacci numbers also exist.

In this article we show how to calculate Fibonacci numbers in Visual Basic .NET.

##  Implementation

This is a very simple recursive implementation, which will become slow on big numbers, because the numbers are recalculated for each recursion.

<<fib>>=
Function fib(ByVal n)
If n < 2 Then Return n Else Return fib(n - 1) + fib(n - 2)
End Function


##  Test

This simple test program will print the first 30 Fibonacci numbers on the console.

It can be compiled from within "Microsoft Visual Studio .NET", or with the VBC.EXE compiler.

<<fibonacci.vb>>=
Imports System.Console

Module Fibonacci
fib

Sub Main()
Dim n As Integer
For n = 1 To 30
WriteLine(n & ":" & fib(n))
Next
End Sub
End Module

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