Macro goes into an infinite loop

There are two sheets in the workbook. First sheet has certain values in a number of rows in a column. The second sheet also has values in each row in repeating patterns in a column. Like this:

   Sheet1          Sheet2
        A                   A
1  AAAA          gre1111assdf
2  BBBB          gfd2222dfhh
3  CCCC         jytjtu3333dgrt
4  DDDD         yufg4444fbth
5  EEEE          sdfs5555gfd

The macro is supposed to go through each row in Sheet2 per each row in the first sheet; assign a certain value to a variable when any given row in Sheet2 includes some other certain values; compare this variable's value to the row value in Sheet1 and quit once this process has been repeated for 4 rows in Sheet1:

Sub GetWpFromXMLs()
Application.ScreenUpdating = False

    Dim sRange As Range '// "source" Range ie. Sheet2
    Dim dRange As Range '// "destination" Range ie. Sheet1

    dRow = 0 '// "destination" Row  ie. Sheet1
    dCol = 2 '// "destination" Column ie. Sheet1
    sRow = 0 '// "source" Row ie. Sheet2
    
    Do
    Set dRange = ActiveSheet.Range("A1").Offset(dRow, 0)
    Set sRange = Sheets("Sheet2").Range("A1").Offset(sRow, 0)

    If InStr(1, sRange, "1111") > 0 Then critName = "AAAA" '// "AAAA" is the value of A1 in Sheet1
    If InStr(1, sRange, "2222") > 0 Then critName = "BBBB" '// "BBBB" is the value of A2 in Sheet1
    If InStr(1, sRange, "3333") > 0 Then critName = "CCCC" '// "CCCC" is the value of A3 in Sheet1
    If InStr(1, sRange, "4444") > 0 Then critName = "DDDD" '// "DDDD" is the value of A4 in Sheet1
    If InStr(1, sRange, "5555") > 0 Then critName = "EEEE" '// "EEEE" is the value of A5 in Sheet1

    If dRange.Value = critName Then '// if the value extracted from the current Row in Sheet2 (sRange) matches the value of the current row in Sheet1 (dRange)
        MsgBox critName '// show what value was extracted
        dRow = dRow + 1 '// since current row in Sheet1 was taken care of, move onto the next row for the next loop
        sRow = 0 '// start over from the first row in Sheet2 in the next loop
    Else
        sRow = sRow + 1 '// since the current row in Sheet2 didn't match the current row in Sheet1, move onto the next row in Sheet2
    End If

    Loop Until dRow = 4 '// stop once first 3 rows in Sheet1 are taken care of

Application.ScreenUpdating = True
End Sub

This is supposed to stop once the match for the 3rd row in Sheet1 is found in Sheet2 but it only happens for the 1st row in Sheet1 and then goes into infinite loop.

I am very confused. Supposed to be that once a match for the first row of Sheet1 is made, dRow is incremented by 1 and thus looking for a match in for the second row of Sheet1 while sRow is reset to 0 so it starts from the first row of Sheet2 so as not to miss any rows. What is wrong here?

It didn't go into an infinite loop for me. I displayed "AAAA", "BBBB", "CCCC", "DDDD" and finished.

I stepped through with F8 and then just let it run (F5).

Not sure what it's trying to achieve but it doesn't loop (more than it should)

Regards

Sub GetWpFromXMLs()
  sq=sheet1.cells(1,1).resize(4)
  sn=sheet2.cells(1,1).resize(4)

  for j=1 to 4
    if switch(instr(sn(j,1),"1111")>0,"AAAA",instr(sn(j,1),"2222")>0,"BBBB",instr(sn(j,1),"3333")>0,"CCCC",instr(sn(j,1),"4444")>0,"DDDD"),instr(sn(j,1),"5555")>0,"EEEE")=sq(j,1) exit for 
  next
  if j<5 then msgbox sn(j,1) & " matches " & sq(j,1)
End Sub

What is interesting is, if you change the first search string from 1111 to 1112 so that it doesn't match, it never goes through the part of the code which increments dRow.

The implication is that it isn't finding what it is looking for.

You could try setting the fourth parameter in INSTR

Regards