I tried all possible solutions and they didn't work. Any help would be appreciated.
Function '' doesn't return a value on all code paths is my error
Public Function Isprime(n2 As Long)
Dim n, i As Integer
Dim b As Boolean
Console.WriteLine("enter a no : \")
n = Console.ReadLine()
i = 2
b = True
While i < n
If n Mod i = 0 Then
b = False
End If
i = i + 1
End While
If b Then
Console.WriteLine("prime no")
Else
Console.WriteLine("not prime no\")
End If
Console.ReadLine()
End Function
Public Function PrimePairs(ByVal n As Long, ByVal n2 As Long) As Integer
Dim count As Integer = 0
Console.ReadLine()
If n Mod 2 = 0 Then
For i = 1 To (n / 2) + 1
n2 = n - i
If Isprime(i) And Isprime(n2) = True Then
count += 1
End If
Next
Else
n2 = n - 2
If Isprime(n2) = True Then
count = +1
End If
End If
Console.WriteLine(count)
Return n
End Function
End Module
You function does not return a value and is quite convoluted. It does I/O and does a prime test at the same time. Separate logic from I/O.
Public Function IsPrime(n As Long) As Boolean
n = Math.Abs(n) ' Allows to consider negative prime numbers
If n < 2 Then ' Disallows -1, 0, 1
Return False
End If
Dim i As Long
i = 2
While i < n ' Note that for n = 2 we don't enter the loop and thus return True.
If n Mod i = 0 Then
Return False
End If
i += 1
End While
Return True
End Function
Also, it is missing a return type. Always work with Option Explicit On for better code quality.
Note that you can return when you hit the first prime factor. There is no point in continuing the loop then.
But there are ways to optimize this. For example we could test the divisibility by 2 separately and then test only odd divisors and it is enough to test divisors up to the square root of n.
Public Function IsPrime(n As Long) As Boolean
n = Math.Abs(n)
If n = 2 Then
Return True
End If
If n < 2 Or n Mod 2 = 0 Then
Return False
End If
Dim i As Long = 3
Dim limit As Long = CLng(Math.Sqrt(n))
While i <= limit
If n Mod i = 0 Then
Return False
End If
i += 2
End While
Return True
End Function
Sub PrimePair()
Dim n As Integer
Dim count As Integer = 0
Console.WriteLine(count)
End Sub
Public Function PrimePairs(ByVal n As Integer, ByVal n2 As Long) As Integer
Dim count As Integer = 0
Console.ReadLine()
If n Mod 2 = 0 Then
For i = 1 To (n / 2) + 1
n2 = CLng(n - i)
If IsPrime(CLng(i)) And IsPrime(n2) = True Then
count += 1
End If
Next
Else
n2 = n - 2
If IsPrime(n2) = True Then
count = +1
End If
End If
Console.WriteLine(count)
Return n
End Function
End Module>
I can't run my code without sub. I created two functions, but the inputs I entered do not return in functions and do not print on the screen, I hope I can solve it, thanks for your attention. My project calculates how many different ways it prints the entered input value as a sum of prime numbers. About the Goldbach conjecture
Is it possible to use Format function to display integers in roman numerals?
For Counter As Integer = 1 To 10
Literal1.Text &= Format(Counter, "???")
Next
This is what I found on http://www.source-code.biz/snippets/vbasic/7.htm
(originally written by Mr Christian d'Heureuse in VB)
I converted it to VB.net:
Private Function FormatRoman(ByVal n As Integer) As String
If n = 0 Then FormatRoman = "0" : Exit Function
' there is no Roman symbol for 0, but we don't want to return an empty string
Const r = "IVXLCDM" ' Roman symbols
Dim i As Integer = Math.Abs(n)
Dim s As String = ""
For p As Integer = 1 To 5 Step 2
Dim d As Integer = i Mod 10
i = i \ 10
Select Case d ' format a decimal digit
Case 0 To 3 : s = s.PadLeft(d + Len(s), Mid(r, p, 1))
Case 4 : s = Mid(r, p, 2) & s
Case 5 To 8 : s = Mid(r, p + 1, 1) & s.PadLeft(d - 5 + Len(s), Mid(r, p, 1))
Case 9 : s = Mid(r, p, 1) & Mid(r, p + 2, 1) & s
End Select
Next
s = s.PadLeft(i + Len(s), "M") ' format thousands
If n < 0 Then s = "-" & s ' insert sign if negative (non-standard)
FormatRoman = s
End Function
I hope this will help others.
Cheers - Dave.
No, there is no standard formatter for that.
If you read the Wikipedia on Roman numerals you'll find that there are multiple ways of formatting Roman Numerals. So you will have to write your own method our use the code of someone else.
I wrote this code that works perfectly up to a million.
You can use it but, please, do not make it your own.
Public NotInheritable Class BRoman
'Written by Bernardo Ravazzoni
Public Shared Function hexRoman(ByVal input As Integer) As String
Return mainROMAN(input)
End Function
Private Shared Function mainROMAN(ByVal input As Integer) As String
Dim under As Boolean = udctr(input)
Dim cifretotali As Integer = input.ToString.Length
Dim output As String = ""
Dim remaning As String = input
Dim cifracor As Integer = cifretotali
While Not cifracor = 0
output = output & coreROMAN(division(remaning, remaning), cifracor)
cifracor = cifracor - 1
End While
If under Then
output = "-" & output
End If
Return output
End Function
Private Shared Function coreROMAN(ByVal num As Integer, ByVal pos As Integer) As String
Dim output As String = ""
Debug.WriteLine(num)
Select Case num
Case 1 To 3
output = say(num, getStringFor(True, pos))
Case 4
output = getStringFor(True, pos) & getStringFor(False, pos)
Case 5 To 8
output = getStringFor(False, pos) & say(num - 5, getStringFor(True, pos))
Case 9, 10
output = say(10 - num, getStringFor(True, pos)) & getStringFor(True, pos + 1)
End Select
Return output
End Function
Private Shared Function getStringFor(ByVal first As Boolean, ByVal index As Integer) As String
Dim output As String = ""
index = index * 2
If first Then
index = index - 1
End If
output = rGetStringFor(index)
Return output
End Function
Private Shared Function rGetStringFor(ByVal index As Integer) As String
Dim output As String = ""
Dim sy As Integer
If index < 8 Then
output = rrGetStringFor(index)
Else
sy = index \ 6
output = say(sy, rrGetStringFor(8)) & rrGetStringFor(((index - 2) Mod 6) + 2) & say(sy, rrGetStringFor(9))
End If
Return output
End Function
Private Shared Function rrGetStringFor(ByVal index As Integer) As String
Dim output As String = ""
Select Case index
Case 1
output = "I"
Case 2 '8
output = "V"
Case 3 '9
output = "X"
Case 4 '10
output = "L"
Case 5 '11
output = "C"
Case 6 '12
output = "D"
Case 7 '13
output = "M"
Case 8
output = "["
Case 9
output = "]"
End Select
Return output
End Function
Private Shared Function division(ByVal inputs As String, ByRef resto As String) As Integer
resto = ""
If inputs.Length > 1 Then
resto = inputs.Substring(1)
End If
Dim output As Integer = Integer.Parse(StrReverse(inputs).Substring(inputs.Length - 1))
Return output
End Function
Public Shared Function say(ByVal index As Integer, ByVal letter As String) As String
Dim output As String = ""
While Not index = 0
output = output & letter
index = index - 1
End While
Return output
End Function
Public Shared Function udctr(ByRef num As Integer) As Boolean
Dim und As Boolean = (num < 0)
If und Then
num = 0 - num
End If
Return und
End Function
End Class
Use the function hexRoman, like this example:
msgbox(Broman.hexRoman(50))
Public Class RomanNumber
Public Shared Function FromNumber(val As Byte) As String
Return GetNumberToRoman(val)
End Function
Public Shared Function FromNumber(val As SByte) As String
Return GetNumberToRoman(val)
End Function
Public Shared Function FromNumber(val As Int16) As String
Return GetNumberToRoman(val)
End Function
Public Shared Function FromNumber(val As Int32) As String
Return GetNumberToRoman(val)
End Function
Public Shared Function FromNumber(val As UInt16) As String
Return GetNumberToRoman(val)
End Function
Public Shared Function FromNumber(val As UInt32) As String
Return GetNumberToRoman(val)
End Function
Public Shared Function ToByte(val As String) As Byte
Return GetNumberFromRoman(val)
End Function
Public Shared Function ToSByte(val As String) As SByte
Return GetNumberFromRoman(val)
End Function
Public Shared Function ToInt16(val As String) As Int16
Return GetNumberFromRoman(val)
End Function
Public Shared Function ToInt32(val As String) As Int32
Return GetNumberFromRoman(val)
End Function
Public Shared Function ToUInt16(val As String) As UInt16
Return GetNumberFromRoman(val)
End Function
Public Shared Function ToUInt32(val As String) As UInt32
Return GetNumberFromRoman(val)
End Function
Private Shared Function GetNumberToRoman(val As Integer) As String
Dim v As String = ""
Do While val > 0
If val >= 1000 Then
v &= "M" : val -= 1000
ElseIf val >= 900 Then
v &= "CM" : val -= 900
ElseIf val >= 500 Then
v &= "D" : val -= 500
ElseIf val >= 400 Then
v &= "CD" : val -= 400
ElseIf val >= 100 Then
v &= "C" : val -= 100
ElseIf val >= 90 Then
v &= "XC" : val -= 90
ElseIf val >= 50 Then
v &= "L" : val -= 50
ElseIf val >= 40 Then
v &= "XL" : val -= 40
ElseIf val >= 10 Then
v &= "X" : val -= 10
ElseIf val >= 9 Then
v &= "IX" : val -= 9
ElseIf val >= 5 Then
v &= "V" : val -= 5
ElseIf val >= 4 Then
v &= "IV" : val -= 4
Else
v &= "I" : val -= 1
End If
Loop
Return v
End Function
Private Shared Function GetNumberFromRoman(val As String) As Object
Dim v As Integer = 0
If val.Contains("IV") Then v += 4 : val = val.Replace("IV", "")
If val.Contains("IX") Then v += 9 : val = val.Replace("IX", "")
If val.Contains("XL") Then v += 40 : val = val.Replace("XL", "")
If val.Contains("XC") Then v += 90 : val = val.Replace("XC", "")
If val.Contains("CD") Then v += 400 : val = val.Replace("CD", "")
If val.Contains("CM") Then v += 900 : val = val.Replace("CM", "")
For Each c As Char In val
If c = "I" Then v += 1
If c = "V" Then v += 5
If c = "X" Then v += 10
If c = "L" Then v += 50
If c = "C" Then v += 100
If c = "D" Then v += 500
If c = "M" Then v += 1000
Next
Return v
End Function
End Class
I have read through the answers here https://stackoverflow.com/a/14332574/44080
I've also tried to produce equivalent VB.net code:
Option Strict ON
Public Function ParseHex(hexString As String) As Byte()
If (hexString.Length And 1) <> 0 Then
Throw New ArgumentException("Input must have even number of characters")
End If
Dim length As Integer = hexString.Length \ 2
Dim ret(length - 1) As Byte
Dim i As Integer = 0
Dim j As Integer = 0
Do While i < length
Dim high As Integer = ParseNybble(hexString.Chars(j))
j += 1
Dim low As Integer = ParseNybble(hexString.Chars(j))
j += 1
ret(i) = CByte((high << 4) Or low)
i += 1
Loop
Return ret
End Function
Private Function ParseNybble(c As Char) As Integer
If c >= "0"C AndAlso c <= "9"C Then
Return c - "0"C
End If
c = ChrW(c And Not &H20)
If c >= "A"C AndAlso c <= "F"C Then
Return c - ("A"C - 10)
End If
Throw New ArgumentException("Invalid nybble: " & c)
End Function
Can we remove the compile errors in ParseNybble without introducing data conversions?
Return c - "0"c Operator '-' is not defined for types 'Char' and 'Char'
c = ChrW(c And Not &H20) Operator 'And' is not defined for types 'Char' and 'Integer'
As it stands, no.
However, you could change ParseNybble to take an integer and pass AscW(hexString.Chars(j)) to it, so that the data conversion takes place outside of ParseNybble.
This solution is much much faster than all the alternative i have tried. And it avoids any ParseNybble lookup.
Function hex2byte(s As String) As Byte()
Dim l = s.Length \ 2
Dim hi, lo As Integer
Dim b(l - 1) As Byte
For i = 0 To l - 1
hi = AscW(s(i + i))
lo = AscW(s(i + i + 1))
hi = (hi And 15) + ((hi And 64) >> 6) * 9
lo = (lo And 15) + ((lo And 64) >> 6) * 9
b(i) = CByte((hi << 4) Or lo)
Next
Return b
End Function
Is there anybody know how to make normal distributed random number in vb.net?
thank you
From this forum post :
Usage:
GaussNumDist(Mean, Standard Deviation, Sample Size)
Code example below, which will populate GaussNumArray() with the sample of numbers, whose distribution will have the mean and standard deviation specified:
Imports System.Math
Module Module1
Friend GaussNumArray() As Double
Friend intICell As Long
Friend Function GaussNumDist(ByVal Mean As Double, ByVal StdDev As Double, ByVal SampleSize As Integer)
intICell = 1 'Loop variable
ReDim GaussNumArray(SampleSize)
Do While (intICell < (SampleSize + 1))
Call NumDist(Mean, StdDev)
Application.DoEvents()
Loop
End Function
Sub NumDist(ByVal meanin As Double, ByVal sdin As Double)
'---------------------------------------------------------------------------------
'Converts uniform random numbers over the region 0 to 1 into Gaussian distributed
'random numbers using Box-Muller algorithm.
'Adapted from Numerical Recipes in C
'---------------------------------------------------------------------------------
'Defining variables
Dim dblR1 As Double
Dim dblR2 As Double
Dim mean As Double
Dim var As Double
Dim circ As Double
Dim trans As Double
Dim dblY1 As Double
Dim dblY2 As Double
Dim Pi As Double
Pi = 4 * Atan(1)
'Get two random numbers
dblR1 = (2 * UniformRandomNumber()) - 1
dblR2 = (2 * UniformRandomNumber()) - 1
circ = (dblR1 ^ 2) + (dblR2 ^ 2) 'Radius of circle
If circ >= 1 Then 'If outside unit circle, then reject number
Call NumDist(meanin, sdin)
Exit Sub
End If
'Transform to Gaussian
trans = Sqrt(-2 * Log(circ) / circ)
dblY1 = (trans * dblR1 * sdin) + meanin
dblY2 = (trans * dblR2 * sdin) + meanin
GaussNumArray(intICell) = dblY1 'First number
'Increase intICell for next random number
intICell = (intICell + 1)
GaussNumArray(intICell) = dblY2 'Second number
'Increase intICell again ready for next call of ConvertNumberDistribution
intICell = (intICell + 1)
End Sub
Friend Function UniformRandomNumber() As Double
'-----------------------------------------------------------------------------------
'Outputs random numbers with a period of > 2x10^18 in the range 0 to 1 (exclusive)
'Implements a L'Ecuyer generator with Bays-Durham shuffle
'Adapted from Numerical Recipes in C
'-----------------------------------------------------------------------------------
'Defining constants
Const IM1 As Double = 2147483563
Const IM2 As Double = 2147483399
Const AM As Double = (1.0# / IM1)
Const IMM1 As Double = (IM1 - 1.0#)
Const IA1 As Double = 40014
Const IA2 As Double = 40692
Const IQ1 As Double = 53668
Const IQ2 As Double = 52774
Const IR1 As Double = 12211
Const IR2 As Double = 3791
Const NTAB As Double = 32
Const NDIV As Double = (1.0# + IM1 / NTAB)
Const ESP As Double = 0.00000012
Const RNMX As Double = (1.0# - ESP)
Dim iCell As Integer
Dim idum As Double
Dim j As Integer
Dim k As Long
Dim temp As Double
Static idum2 As Long
Static iy As Long
Static iv(NTAB) As Long
idum2 = 123456789
iy = 0
'Seed value required is a negative integer (idum)
Randomize()
idum = (-Rnd() * 1000)
'For loop to generate a sequence of random numbers based on idum
For iCell = 1 To 10
'Initialize generator
If (idum <= 0) Then
'Prevent idum = 0
If (-(idum) < 1) Then
idum = 1
Else
idum = -(idum)
End If
idum2 = idum
For j = (NTAB + 7) To 0
k = ((idum) / IQ1)
idum = ((IA1 * (idum - (k * IQ1))) - (k * IR1))
If (idum < 0) Then
idum = (idum + IM1)
End If
If (j < NTAB) Then
iv(j) = idum
End If
Next j
iy = iv(0)
End If
'Start here when not initializing
k = (idum / IQ1)
idum = ((IA1 * (idum - (k * IQ1))) - (k * IR1))
If (idum < 0) Then
idum = (idum + IM1)
End If
k = (idum2 / IQ2)
idum2 = ((IA2 * (idum2 - (k * IQ2))) - (k * IR2))
If (idum2 < 0) Then
idum2 = idum2 + IM2
End If
j = (iy / NDIV)
iy = (iv(j) - idum2)
iv(j) = idum
If (iy < 1) Then
iy = (iy + IMM1)
End If
temp = AM * iy
If (temp <= RNMX) Then
'Return the value of the random number
UniformRandomNumber = temp
End If
Next iCell
End Function
End Module
You can use following line
Dim x1 as Double = MathNet.Numerics.Distributions.Normal.Sample(MEAN, STDEV)
Math.Net Numeric package can be installed using following NuGet command
Install-Package MathNet.Numerics -Version 4.9.0
You can found more information on NuGet site