First split then join a subset of a string

Since the _ after the thumb is always the first instance then Substring should be perfectly viable in conjunction with IndexOf.

string newString = myString.Substring(myString.IndexOf("_") + 1);

This should take the substring starting at the character immediately following the first instance of the _ character.

If you wish to get the second index of _, here's what I recommend:

int first = myString.IndexOf("_");
int second = mystring.Substring(first).IndexOf("_");

See this answer by Jon Skeet to the question "Index of the nth occurrence of a string?" for support for this approach.

If you don't like indexOf, but want Join instead:

String.Join("_",
   "thumb_634735515600845357tchayat_november_200612.jpg"
   .Split('_')
   .Skip(1)
   .ToArray())

After splitting and rearranging you can use Join method.

string new_value=String.Join("",your_array);

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