Finding String of Substring in VB without using library function - vb.net

Question

I am little bit confused in this program.
I am new to Visual Basic but intermediate to C.
Actually I want to get sub-string of string without using library function of Visual Basic.
Here is the C source code I also given my VB code too.
1.The Program will get two inputs from user i.e A & B
2. Than Find the substring from B.
3. Finally Print the result.
int i,j=0,k=0,substr=0;
for(i=0;i<strlen(a);i++)
{
if(a[i]==b[j])
{
j++;
if(b[j]==0)
{
printf("second string is substring of first one");
substr=1;
break;
}
}
}
for(i=0;i<strlen(b);i++)
{
if(b[i]==a[k])
{
k++;
if(a[k]==0)
{
printf(" first string is substring of second string");
substr=1;
break ;
}
}
}
if(substr==0)
{
printf("no substring present");
}
While my code is
Dim a As String
Dim b As String
a = InputBox("Enter First String", a)
b = InputBox("Enter 2nd String", b)
Dim i As Integer
Dim j As Integer = 0
Dim k As Integer = 0
Dim substr As Integer = 0
For i = 0 To a.Length - 1
If a(i) = b(j) Then
j += 1
If b(j) = 0 Then
MsgBox("second string is substring of first one")
substr = 1
Exit For
End If
End If
Next i
For i = 0 To b.Length - 1
If b(i) = a(k) Then
k += 1
If a(k) = 0 Then
MsgBox(" first string is substring of second string")
substr = 1
Exit For
End If
End If
Next i
If substr = 0 Then
MsgBox("no substring present")
End If
End Sub
While compiling it gives following debugging errors.
Line Col
Error 1 Operator '=' is not defined for types 'Char' and 'Integer'. 17 24
Error 2 Operator '=' is not defined for types 'Char' and 'Integer'. 27 24

Answer 1

Part of your confusion is that .Net strings are much more than just character buffers. I'm going to assume that you can at least use strings. If you can't, use need to declare character arrays instead. That out of the way, this should get you there as a 1:1 translation:
Private Shared Function search(ByVal a As String, ByVal b As String) As Integer
Dim i As Integer = 0
Dim j As Integer = 0
Dim firstOcc As Integer
While i < a.Length
While a.Chars(i)<>b.Chars(0) AndAlso i < a.Length
i += 1
End While
If i >= a.Length Then Return -1 'search can not continue
firstOcc = i
While a.Chars(i)=b.Chars(j) AndAlso i < a.Length AndAlso j < b.Length
i += 1
j += 1
End While
If j = b.Length Then Return firstOcc
If i = a.Length Then Return -1
i = firstOcc + 1
j = 0
End While
Return 0
End Function
Shared Sub Main() As Integer
Dim a As String
Dim b As String
Dim loc As Integer
Console.Write("Enter the main string :")
a = Console.ReadLine()
Console.Write("Enter the search string :")
b = Console.ReadLine()
loc = search(a, b)
If loc = -1 Then
Console.WriteLine("Not found")
Else
Console.WriteLine("Found at location {0:D}",loc+1)
End If
Console.ReadKey(True)
End Sub
But please don't ever actually use that. All you really need is this:
Private Shared Function search(ByVal haystack as String, ByVal needle As String) As Integer
Return haystack.IndexOf(needle)
End Function

Answer 2

VB has a built-in function called InStr, it's part of the language. It returns an integer specifying the start position of the first occurrence of one string within another.
http://msdn.microsoft.com/en-us/library/8460tsh1(v=VS.80).aspx
Pete

Answer 3

Try this one, this will return a List(Of Integer) containing the index to all occurrence's of the find text within the source text, after the specified search starting position.
Option Strict On
Public Class Form1
''' <summary>
''' Returns an array of indexes where the find text occurred in the source text.
''' </summary>
''' <param name="Source">The text you are searching.</param>
''' <param name="Find">The text you are searching for.</param>
''' <param name="StartIndex"></param>
''' <returns>Returns an array of indexes where the find text occurred in the source text.</returns>
''' <remarks></remarks>
Function FindInString(Source As String, Find As String, StartIndex As Integer) As List(Of Integer)
If StartIndex > Source.Length - Find.Length Then Return New List(Of Integer)
If StartIndex < 0 Then Return New List(Of Integer)
If Find.Length > Source.Length Then Return New List(Of Integer)
Dim Results As New List(Of Integer)
For I = StartIndex To (Source.Length) - Find.Length
Dim TestString As String = String.Empty
For II = I To I + Find.Length - 1
TestString = TestString & Source(II)
Next
If TestString = Find Then Results.Add(I)
Next
Return Results
End Function
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Try
Dim Search As String = "Hello world, this world is an interesting world"
Dim Find As String = "world"
Dim Indexes As List(Of Integer) = New List(Of Integer)
Try
Indexes = FindInString(Search, Find, 0)
Catch ex As Exception
MsgBox(ex.ToString)
End Try
RichTextBox1.Text = "Search:" & vbCrLf
RichTextBox1.Text = RichTextBox1.Text & Search & vbCrLf & vbCrLf
RichTextBox1.Text = RichTextBox1.Text & "Find:" & vbCrLf
RichTextBox1.Text = RichTextBox1.Text & Find & vbCrLf & vbCrLf
RichTextBox1.Text = RichTextBox1.Text & "-----------" & vbCrLf
RichTextBox1.Text = RichTextBox1.Text & "Result Indexes:" & vbCrLf & vbCrLf
For Each i As Integer In Indexes
RichTextBox1.Text = RichTextBox1.Text & i.ToString & vbCr
Next
Catch ex As Exception
MsgBox(ex.ToString)
End Try
End Sub
End Class
Here is another way, where there is no use of .Net functions.
Function FindInString(Source As String, Find As String, StartIndex As Integer) As Integer()
If StartIndex > Len(Source) - Len(Find) Then Return {}
If StartIndex < 0 Then Return {}
If Len(Find) > Len(Source) Then Return {}
Dim Results As Integer() = {}, ResultCount As Integer = -1
For I = StartIndex To Len(Source) - Len(Find)
Dim TestString As String = ""
For II = I To I + Len(Find) - 1
TestString = TestString & Source(II)
Next
If TestString = Find Then
ResultCount += 1
ReDim Preserve Results(ResultCount)
Results(ResultCount) = I
End If
Next
Return Results
End Function