hi. i'm trying to write a sudoku puzzle generator with vb.net but my algorithm seems correct, but runs out of numbers at some stages while generating the puzzle. can anyone look into ma code and see why?

Public Class home
    Public rp = 0, arr(8,  As Integer, rsv(8,  As List(Of Integer), ax(2, 2)

    Public Function sot(ByRef ar As Array)
        Dim o, p, q, r
        For o = 0 To 8
            If (ar(o) = Nothing) Then
                For p = o To 1 Step -1
                    q = ar(p)
                    r = ar(p - 1)
                    ar(p) = r
                    ar(p - 1) = q
                Next
            End If
        Next
        Return Nothing
    End Function

    Public Function rnd(ByVal x As Integer, ByVal y As Integer)
        Dim r1 = Nothing, rd As New Random
        For a As Integer = 0 To 8
            If (arr(x, a) <> 0 And rsv(x, y).IndexOf(arr(x, a)) <> -1) Then
                rsv(x, y).RemoveAt(rsv(x, y).IndexOf(arr(x, a)))
            End If

            If (arr(a, y) <> 0 And rsv(x, y).IndexOf(arr(a, y)) <> -1) Then
                rsv(x, y).RemoveAt(rsv(x, y).IndexOf(arr(a, y)))
            End If
        Next

        If (x >= 0 And x <= 2 And y >= 0 And y <= 2) Then
            For a1 As Integer = 0 To 2
                For b1 As Integer = 0 To 2
                    If (arr(a1, b1) <> Nothing And rsv(x, y).IndexOf(arr(a1, b1)) <> -1) Then
                        rsv(x, y).RemoveAt(rsv(x, y).IndexOf(arr(a1, b1)))
                    End If
                Next
            Next
        End If
        If (x >= 0 And x <= 2 And y >= 3 And y <= 5) Then
            For a1 As Integer = 0 To 2
                For b1 As Integer = 3 To 5
                    If (arr(a1, b1) <> Nothing And rsv(x, y).IndexOf(arr(a1, b1)) <> -1) Then
                        rsv(x, y).RemoveAt(rsv(x, y).IndexOf(arr(a1, b1)))
                    End If
                Next
            Next
        End If
        If (x >= 0 And x <= 2 And y >= 6 And y <=  Then
            For a1 As Integer = 0 To 2
                For b1 As Integer = 6 To 8
                    If (arr(a1, b1) <> Nothing And rsv(x, y).IndexOf(arr(a1, b1)) <> -1) Then
                        rsv(x, y).RemoveAt(rsv(x, y).IndexOf(arr(a1, b1)))
                    End If
                Next
            Next
        End If

        If (x >= 3 And x <= 5 And y >= 0 And y <= 2) Then
            For a1 As Integer = 3 To 5
                For b1 As Integer = 0 To 2
                    If (arr(a1, b1) <> Nothing And rsv(x, y).IndexOf(arr(a1, b1)) <> -1) Then
                        rsv(x, y).RemoveAt(rsv(x, y).IndexOf(arr(a1, b1)))
                    End If
                Next
            Next
        End If
        If (x >= 3 And x <= 5 And y >= 3 And y <= 5) Then
            For a1 As Integer = 3 To 5
                For b1 As Integer = 3 To 5
                    If (arr(a1, b1) <> Nothing And rsv(x, y).IndexOf(arr(a1, b1)) <> -1) Then
                        rsv(x, y).RemoveAt(rsv(x, y).IndexOf(arr(a1, b1)))
                    End If
                Next
            Next
        End If
        If (x >= 3 And x <= 5 And y >= 6 And y <=  Then
            For a1 As Integer = 3 To 5
                For b1 As Integer = 6 To 8
                    If (arr(a1, b1) <> Nothing And rsv(x, y).IndexOf(arr(a1, b1)) <> -1) Then
                        rsv(x, y).RemoveAt(rsv(x, y).IndexOf(arr(a1, b1)))
                    End If
                Next
            Next
        End If

        If (x >= 6 And x <= 8 And y >= 0 And y <= 2) Then
            For a1 As Integer = 6 To 8
                For b1 As Integer = 0 To 2
                    If (arr(a1, b1) <> Nothing And rsv(x, y).IndexOf(arr(a1, b1)) <> -1) Then
                        rsv(x, y).RemoveAt(rsv(x, y).IndexOf(arr(a1, b1)))
                    End If
                Next
            Next
        End If
        If (x >= 6 And x <= 8 And y >= 3 And y <= 5) Then
            For a1 As Integer = 6 To 8
                For b1 As Integer = 3 To 5
                    If (arr(a1, b1) <> Nothing And rsv(x, y).IndexOf(arr(a1, b1)) <> -1) Then
                        rsv(x, y).RemoveAt(rsv(x, y).IndexOf(arr(a1, b1)))
                    End If
                Next
            Next
        End If
        If (x >= 6 And x <= 8 And y >= 6 And y <=  Then
            For a1 As Integer = 6 To 8
                For b1 As Integer = 6 To 8
                    If (arr(a1, b1) <> Nothing And rsv(x, y).IndexOf(arr(a1, b1)) <> -1) Then
                        rsv(x, y).RemoveAt(rsv(x, y).IndexOf(arr(a1, b1)))
                    End If
                Next
            Next
        End If

        Try
            arr(x, y) = rsv(x, y)(rd.Next(0, rsv(x, y).Count))
        Catch ex As Exception

        End Try
        Return Nothing
    End Function

    Private Sub home_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim a = 0, b = 0, c = 0, n
        For a = 0 To 8
            For b = 0 To 8
                n = "s" & a & b
                rsv(a, b) = New List(Of Integer)
                For c = 1 To 9
                    rsv(a, b).Add(c)
                Next
                rnd(a, b)
                Panel2.Controls.Item(n).text = arr(a, b)
            Next
        Next

    End Sub

    Private Sub RefreshToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles RefreshToolStripMenuItem.Click
        rp = 0
        Array.Clear(arr, 0, 81)
        home_Load(Nothing, Nothing)
    End Sub
End Class

i've attached screen shots, the "0" in the puzzle are the places where the algorithm runs out of numbers to put cos the next number to put cannot be placed there due to the rules of sudoku. i need help guys!

I wrote one of these in Java over a year ago.
You have to use a backtracking algorithm.
Set up the rules. Make the algorithm fill in the slots with random numbers line by line. When it gets stuck it should go back a random number of steps(nothing large else you get "array out of bounds").

I will try to find my code, or write it again if I can find the time.

Had to write it again.
Java code.

import java.util.Random;


public class Main {


    public static void main(String[] args) {

        int[][] grid= new int[9][9];
        //change random seed to get a differnet grid
        Random rand= new Random(99);
        int count=0;
        int failCount=0;
        while(count<81)
        {
            boolean fail=false;
            //generate number
            int temp=rand.nextInt(9)+1;
            //check horizontal
            for(int i=0;i<count%9;i++)
                if(temp==grid[i][count/9])
                {
                    fail=true;
                    failCount++;
                    break;
                }
            //check vertical
            for(int i=0;i<count/9;i++)
                if(temp==grid[count%9][i])
                {
                    fail=true;
                    failCount++;
                    break;
                }
            //check 3x3
            for(int i=(count%9)/3*3;i<(count%9)/3*3+3;i++)
                for(int j=(count/9)/3*3;j<(count/9)/3*3+3;j++)
                    if(temp==grid[i][j])
                    {
                        fail=true;
                        failCount++;
                        break;
                    }
            //if stuck  then backtrack    
            if(failCount>40)
            {
                int x=rand.nextInt(50)+9;
                for(int i=0;i<x && count>0;i++)
                {
                    grid[count%9][count/9]=0;
                    count--;
                }
                failCount=0;
                
            }
                    
            // all clear then add new number to the grid
            if(fail==false)
            {
                grid[count%9][count/9]=temp;
                count++;
                failCount=0;
            }
        }
        
        for(int i=0;i<9;i++)
        {
            for(int j=0;j<9;j++)
            {
                System.out.print(grid[i][j]);
            }
             System.out.println();
        }
    }

}

ok, i'd see if i can convert the java codes into vb. thanks for the input!

tried ya code, still didnt work man!