Split string based on the first occurrence of the character
You can use Substring to get both parts separately.
First, you use IndexOf to get the position of the first comma, then you split it :
string input = "101,a,b,c,d";int firstCommaIndex = input.IndexOf(',');string firstPart = input.Substring(0, firstCommaIndex); //101string secondPart = input.Substring(firstCommaIndex + 1); //a,b,c,dOn the second part, the +1 is to avoid including the comma.