Passing a parameter to an sql stored procedure in c#

If you want to call a stored procedure using a SqlCommand, do not execute EXEC GetIslemIdleri, execute just GetIslemIdleri, setting CommandType to CommandType.StoredProcedure:

cmd = new SqlCommand("GetIslemIdleri", sqlConn);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add(new SqlParameter("@CARIID", 110));

using (var reader = cmd.ExecuteReader()) //error occurs here
{
    while (reader.Read())
    {
        islemidleri.Add(reader.GetInt32(0));
    }
}

you forgot to add the prodecure`s name:

cmd.CommandType = CommandType.StoredProcedure;
cmd.CommandText = "GetIslemIdleri";
cmd.Parameters.Add("@CARIID", SqlDBType.Int).Value = 110;

And do procedure as:

CREATE PROCEDURE [dbo].[GetIslemIdleri] 
(
    @CARIID int 
)
AS
BEGIN
SET NOCOUNT ON;    
SELECT ID FROM TBLP1ISLEM WHERE TBLP1ISLEM.CARI_ID = @CARIID
END

This has to work.

You need to make sure your SqlCommand is set to CommandType.StoredProcedure.

cmd.CommandType = CommandType.StoredProcedure