Run Macro if mandatory SHeet name exist - excel

Question

I have a macro and its dependent on Specific sheet name 'PRODUCTS45' problem is if a user run the macro on different sheet e.g. Sheet1 it throws debug error.
can anyone help me to make macro run only when sheet 'PRODUCTS45' is present and if not throws msgbox that mandatory sheet is not present.
Option Explicit
Sub FlagWord()
Dim R As Range, WS As Worksheet
Dim RE As Object
Dim C As Range, D As Range
Dim S As String
Dim I As Long, J As Long
S = InputBox("Enter desired word")
'Current filled in range
Set WS = Worksheets("SHEET")
'case sensitive sheet name and its required to run macro if this is not present macro should not run
With WS
Set R = .Range(.Cells(1, 1), .Cells(.Rows.Count, 1).End(xlUp))
Set R = R.Resize(columnsize:=.Cells(1, .Columns.Count).End(xlToLeft).Column)
End With
If Not S = "" Then
'If S not present then add column
With WS.Rows(1)
Set C = .Find(what:=S, after:=.Cells(1, 1), LookIn:=xlValues, _
lookat:=xlWhole, searchorder:=xlByColumns, searchdirection:=xlNext, MatchCase:=False)
End With
'Add column if not already present
If C Is Nothing Then
Set R = R.Resize(columnsize:=R.Columns.Count + 1)
R(1, R.Columns.Count) = S
End If
End If 'no new column if S is blank
'do the word match
'Clear the data area
With R
.Offset(1, 1).Resize(.Rows.Count - 1, .Columns.Count - 1).ClearContents
End With
'fill in the data
'use regex to allow for easy word boundaries
Set RE = CreateObject("vbscript.regexp")
With RE
.Global = False 'only need a single match
.ignorecase = True
For Each C In R.Columns(1).Offset(1, 0).Resize(R.Rows.Count - 1).Cells
For Each D In R.Rows(1).Offset(0, 1).Resize(columnsize:=R.Columns.Count - 1).Cells
.Pattern = "\b" & D.Text & "\b"
If .test(C.Text) = True Then
R(C.Row, D.Column) = "YES"
End If
Next D
Next C
End With
End Sub

Answer 1

How about something like this:
Public Sub CheckForSheetBeforeCallingFlagWord()
Dim ws As Worksheet
Dim bolFound As Boolean
bolFound = False
For Each ws In ThisWorkbook.Worksheets
If ws.Name = "PRODUCTS45" Then bolFound = True
Next ws
If bolFound = False Then
MsgBox "Required sheet 'PRODUCTS45' not found." & Chr(10) & "Aborting..."
Exit Sub
End If
Call flagword
End Sub
This procedure checks for the existence of the required sheet. If it is not found then you get a message box and nothing else happens. If the sheet is found then the other procedure gets called (and executed).

Answer 2

Trying to reference a worksheet that doesn't exist will throw an error. You can use an error handler to trap this and give the desired message.
Sub myMacro()
On Error GoTo sheetNotFound
doStuff ThisWorkbook.Sheets("PRODUCTS45")
Exit Sub
sheetNotFound:
MsgBox "PRODUCTS45 not found"
End Sub
Sub doStuff(ws As Worksheet)
' remaining code goes here
End Sub