replace space with underscore

Here is a Function that works in Excel VBA for your purpose:

Function FindAndReplace(strSource As String, strFind As String, strReplace As String)
Dim i As Long, temp As String
temp = strSource
Do
i = InStr(1, temp, strFind)
If i = 0 Then Exit Do
    temp = Left(temp, i - 1) & strReplace & Right(temp, Len(temp) - i - Len(strFind) + 1)
Loop
FindAndReplace = temp
End Function

there is a built-in function in vba

Function Replace(Expression As String, Find As String, Replace As String, [Start As Long = 1], [Count As Long = -1], [Compare As VbCompareMethod = vbBinaryCompare]) As String
    Member of VBA.Strings
    Find and replace a substring within a string

eg:-
    Replace("Replacing this string with underscore", " ", "_")

Right you are gafoorgk--and it's a much better solution than my function

Below is a basic search and replace program

Replacing this string with underscore"  into "Replacing_this_string_with_underscore
Below is a basic search and replace program

Private Sub cmdrepl_Click()
    Dim strTemp As String
    Dim strSrch As String
    Dim strRepl As String

    strTemp = "Replacing this string with underscore"
    strSrch = " "
    strRepl = "_"

   'replace all occurrences of 'strSrch' in 'strTemp' with 'strRepl'
    strTemp = Replace(strTemp, strSrch, strRepl)
End Sub


In this code it is incoporated into a button click routine with hardcoded values in the function
Private Sub cmdrepl_Click()
        txtnewstr.Text = Replace(txtOrigStr, " ", "_")
        txtnewstr.Refresh
End Sub