How to pass string array in SQL parameter to IN clause in SQL

Introduction: Even though the OP already accepted an answer, I thought it would be better to share my experience, because I belive the approach I’m about to show is better then the one accepted.

I find that the best way to pass Arrays to sql server database is using a user defined table type and c# DataTable.
In your case, since you want to pass a string array of one dimension, it’s fairly easy:

First you need to create a user defined table type in your database:

 CREATE TYPE dbo.StringArray As Table (
    StringItem varchar(50) -- you can use any length suited for your needs
)

Then you need to create a datatable in your c# code:

DataTable dt = new DataTable();
dt.Columns.Add("StringItem", typeof(System.String));

Then change your stored procedure to accept this data type as a parameter:

ALTER proc [dbo].[sp_Accessories]
(  
@Mode varchar(50)=null,
@id int=null,
@brand varchar(50)=null,
@department varchar(MAX)=null,
@season varchar(50)=null,
@groupname varchar(MAX)=null,
@styles varchar(50)=null,
@combo dbo.StringArray Readonly=null, -- NOTE THIS CHANGE
@combo_color nvarchar(max)=null,
)
as
if @Mode="getsizewise"
begin
select Sizes,SUM(Quantity) from tbl_SizeBreakup where (Brand=@brand) and
(Department=@department) and (Season=@season) and (Group_Name=@groupname) and (Style=@styles) 
and (Combo_Color=@color) and (Total_Add_Qty='Total Quantity') 
and comboColumn in(select StringItem from @Combo) -- NOTE THIS CHANGE
Group By Sizes
end

Then you need to convert the string array to a dataTable in your c# code.

foreach (string s in YourStringArray) {
    string[] temp = {s};
    dt.Rows.Add(temp);
}

Add the DataTable as a parameter to the stored procedure:

System.Data.SqlClient.SqlParameter sp = new Data.SqlClient.SqlParameter();
sp.SqlDbType = SqlDbType.Structured;
sp.Value = dt;
sp.ParameterName = "@Combo";
cmd.Parameters.Add(sp);

Build and run.

This approach should have better performance then using an sql user defined function, and also can be used for different data types. this is one of the best reasons to use it:
Consider a scenario where you need to pass an array of Dates: the csv approach requires sql to convert each string to a date, while with this approach you can simply pass the dates as is, without converting them to strings and then back to dates.Also, you can pass 2 dimensions array or dictionaries, all you have to do is create the appropriate user defined data type in your sql database.

Note: code written directly here, there might be some typos.