Replacing Characters With......?

Hi,
Would someone help me on this?
I want to type an:
"A" and printed as "A" on RichTextBox
"B" and printed as "B" on RichTextBox where I have characters "AB".(This part is very easy for me!)
But If I type:
"B" and printed as "B" on RichTextBox
"A" and printed as "A" on RichTextBox where I Should have characters "BA". But I do not want "BA" there. I want "BA" replaced by a character "C". (This part is very very hard for me!)
I really appreciate any kind of feed back on this.
Thanx
nagu

Ps: Please pay attention to sequences

Try this:

VB Code:

Private RichTextBox1_Change()
    With RichTextBox1
         If InStr(1, .Text, "BA") Then .Text = Replace(.Text, "BA", "C")
    End With
End Sub

You don't need to search for the string. Replace() will do it automatically. This method will also preserve the SelStart position.

VB Code:

Private Sub RichTextBox1_Change()
    lStart = RichTextBox1.SelStart
    RichTextBox1.Text = Replace(RichTextBox1.Text, "BA", "C")
    RichTextBox1.SelStart = lStart
End Sub