>Is there an easy way to compare two string and return what is different ?
>
>stringWichWorks = "http://tira-teima.as.bol.uol.com.br/challengeSender.html?data=SDTMliZ2VLTDiJ3yTOaiSZh6WBKgWVDlKeve0zmxTD7R13tPNpa7yMjzYWRHbQVpX5VvFcwbpsHDpPPvw6maOA1aJbRIgoi7jCTPBoQ647LHvOFZZb9fHOP7SE4Jr0cexq2QFe0Xy89GPolE5sPmrA=="
>
>stringWichFails = "http://tira-teima.as.bol.uol.com.br/challengeSender.html?data=SDTMliZ2VLTDiJ3yTOaiSZh6WBKgWVDlKeve0zmxTD7R13tPNpa7yMjzYWRHbQVpX5VvFcwbpsHD0ApPPvw6maOA1aJbRIgoi7jCTPBoQ647LHvOFZZb9fHOP7SE4Jr0cexq2QFe0Xy89GPolE5sPmrA=="

Depends on your definition of different, and I mean it.

You can start with something as simple as comparing them to the first different byte:

for i=1 to min(len(str1), len(str2))
   c1=left(str1, i)
   c2=left(str2, i)
   if not c1==c2
      ? "First",i,"characters are identical"
      ? substr(c1, i+1)
      ? substr(c2, i+1)
      exit
   endif
endfor