RosettaCodeData/Task/Fibonacci-sequence/FreeBASIC/fibonacci-sequence.basic

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'Fibonacci extended
'Freebasic version 24 Windows
Dim Shared ADDQmod(0 To 19) As Ubyte
Dim Shared ADDbool(0 To 19) As Ubyte
For z As Integer=0 To 19
ADDQmod(z)=(z Mod 10+48)
ADDbool(z)=(-(10<=z))
Next z
Function plusINT(NUM1 As String,NUM2 As String) As String
Dim As Byte flag
#macro finish()
three=Ltrim(three,"0")
If three="" Then Return "0"
If flag=1 Then Swap NUM2,NUM1
Return three
Exit Function
#endmacro
var lenf=Len(NUM1)
var lens=Len(NUM2)
If lens>lenf Then
Swap NUM2,NUM1
Swap lens,lenf
flag=1
End If
var diff=lenf-lens-Sgn(lenf-lens)
var three="0"+NUM1
var two=String(lenf-lens,"0")+NUM2
Dim As Integer n2
Dim As Ubyte addup,addcarry
addcarry=0
For n2=lenf-1 To diff Step -1
addup=two[n2]+NUM1[n2]-96
three[n2+1]=addQmod(addup+addcarry)
addcarry=addbool(addup+addcarry)
Next n2
If addcarry=0 Then
finish()
End If
If n2=-1 Then
three[0]=addcarry+48
finish()
End If
For n2=n2 To 0 Step -1
addup=two[n2]+NUM1[n2]-96
three[n2+1]=addQmod(addup+addcarry)
addcarry=addbool(addup+addcarry)
Next n2
three[0]=addcarry+48
finish()
End Function
Function fibonacci(n As Integer) As String
Dim As String sl,l,term
sl="0": l="1"
If n=1 Then Return "0"
If n=2 Then Return "1"
n=n-2
For x As Integer= 1 To n
term=plusINT(l,sl)
sl=l
l=term
Next x
Function =term
End Function
'============== EXAMPLE ===============
print "THE SEQUENCE TO 10:"
print
For n As Integer=1 To 10
Print "term";n;": "; fibonacci(n)
Next n
print
print "Selected Fibonacci number"
print "Fibonacci 500"
print
print fibonacci(500)
Sleep