CSHARP

how consider the first caracter in Split c#

Considerar somente a primeira string especificada para realizar o split
You can specify how many substrings to return using string.Split:

string myString = "101.a.b.c.d"

var pieces = myString.Split(new[] { '.' }, 2);
Returns:

101
a.b.c.d

split at first index of a char c#

var pieces = myString.Split(new[] { ',' }, 2);